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DIY Stompboxes => Building your own stompbox => Topic started by: merlinb on April 21, 2012, 10:17:37 AM

Title: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 21, 2012, 10:17:37 AM
For a long time I've felt guilty that my pedal board didn't include a compressor. Finally, after about a year of breadboarding, I have produced a circuit that can take on a Dynacomp and win, boasting:

Despite its final simplicity, I went though just about every possible configuration of OTA while chasing acceptable performance. As you can see from the schem, the OTA is working as a current-controlled resistor in the feedback loop of an opamp. This reduces the contribution of OTA noise.

The input signal is also coupled directly to the side chain, which consists of a precision rectifier (U1b) and precision current source (U2a) that dumps more current into the OTA control pin as the audio signal gets larger.

The ratio control blends compressed and uncompressed signals, so its variable from zero to infinite ratio (limiting)! I actually built two versions of this, one with threshold the other with ratio, but I found that basically the same sounds obtain with either, depending on how you use them, so I will probably sell one of them.

More info, sound clip and PCB layouts can be found here: http://valvewizard.co.uk/engineersthumb.html
I'm now working on a five-knob version with VU meter...

(http://www.freewebs.com/valvewizard2/engineersthumbschem.jpg)

(http://i81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/engineersthumb1.jpg)

(http://i81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/CIMG7128.jpg)
Title: Vero layout
Post by: merlinb on April 21, 2012, 10:18:09 AM
(http://i81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/engineersthumbvero.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: frequencycentral on April 21, 2012, 11:03:40 AM
Clever bugger!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: alfafalfa on April 21, 2012, 11:04:19 AM
This is really great !!

Will there also be a pcb version ?  I always etch my boards.

Thanks
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 21, 2012, 11:05:22 AM
Will there also be a pcb version ?  I always etch my boards.
Yes, there is a link in the first post.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Slade on April 21, 2012, 11:14:43 AM
merlin, your compressor looks awesome, very cool design.
Did you tried release and attack pots? How do they behave?

Thanks a lot for your work, can't wait to try it!!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: sugonidamaso on April 21, 2012, 11:19:26 AM
Wow! Great work merlin! Cool sound! Let me check if there's 13700's here in my area.built a dynacomp couple of years back (CA3080 costly :icon_mrgreen:) Thank you!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Earthscum on April 21, 2012, 11:51:56 AM
Nice design.

So, what are you doing with the other half of the OTA? Funkee idea: use other half to build an "expander" of some sort using the same idea as the comp. "Expand In/Out" and "Comp In/Out", 2-in-1. I know there's simpler chips that do just this out there, but if they were that great, you wouldn't have had a reason to design something "better", obviously.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on April 21, 2012, 12:08:00 PM
Nice one Wiz! Top of the to-do list.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Steve Mavronis on April 21, 2012, 12:19:11 PM
Nice original design and sound clip demo good! I'm not familiar with a symbol on your schematic. What is the double circle thing?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 21, 2012, 01:10:04 PM
Quote
Did you tried release and attack pots? How do they behave?
Yes, in the 5-knob version I am using 1M log pots for both (with a 220k resistor in series with the release pot), and they behave perfectly. Very long attack times are possible!

Nice original design and sound clip demo good! I'm not familiar with a symbol on your schematic. What is the double circle thing?
The double circle is the IEC symbol for a current source, so if you bolt that onto a generic opamp symbol you get the usual symbol for an operational transcondutance amplifier. It takes the voltage difference between its inputs (like an opamp) and converts into into a current output.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kaycee on April 21, 2012, 01:21:36 PM
Thanks for sharing, cool project indeed!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: BubbaFet on April 21, 2012, 01:31:52 PM
Brilliantly elegant !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Steve Mavronis on April 21, 2012, 01:39:35 PM
The double circle is the IEC symbol for a current source, so if you bolt that onto a generic opamp symbol you get the usual symbol for an operational transcondutance amplifier. It takes the voltage difference between its inputs (like an opamp) and converts into into a current output.

Ah, on the MXR Dyna Comp factory schematic they didn't do that for the CA3080. Learn something new every day.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: head_spaz on April 21, 2012, 01:45:24 PM
VERY nice Merlin!
You really do design the BEST toys !!!
Thank you!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Earthscum on April 21, 2012, 01:47:05 PM
I'm not sure if it's universally correct, but whenever I draw any OTA, I use the circles, and include (in hand drawings) a dash for the diode bias pin between the in and out for the ones that use it. That lets me thumb through and know the item is an OTA (of some sort), and the dash usually lets me know it's something like a LM13x00.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cliff Schecht on April 21, 2012, 02:14:37 PM
Why not cut down on op amp count and use the OTA for the envelope follower or expo current source? A FET could buffer the 4.5V reference just as well as the op amp circuit and you could maybe shrink the overall footprint of the design a bit. Just a thought..
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonasx26 on April 21, 2012, 02:23:45 PM
Cool design! The sidechain and overall response is very linear. I really like it. Thanks a lot for sharing!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mike Burgundy on April 21, 2012, 02:24:56 PM
There's also the two on-board darlington buffers that you could still put to some use. The fact that there's two of everything on a chip begs a multi-band ;)
Nice work, brilliant workaround for OTA noise. Gotta build me one of these - thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bonaventura on April 21, 2012, 02:32:40 PM
pls enlighten me,

Vref is coming out fm an opamp,in this case what is the significance of U2B?

thanks.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cliff Schecht on April 21, 2012, 02:42:22 PM
Vref itself is coming from the 1/2 supply divider and U2B is buffering this because it is used in a lot of places. If any of the 4.5V reference circuits draw current from the resistor divider it can cause the reference voltage to move around. The buffer provides a low impedance output which keep the reference voltage at 4.5V pretty much regardless of current draw (within reason).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Hammer on April 21, 2012, 03:08:55 PM
Hats off, my friend.  Hats off. :icon_biggrin:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on April 21, 2012, 03:13:30 PM
Very nice!  This is probably one of those "duh!" questions, but here goes:

I don't see IC2/U2 on the Vero layout. Is the Vero an equivalent circuit to the schematic and operates the same without IC2?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on April 21, 2012, 03:18:36 PM
Very nice!  This is probably one of those "duh!" questions, but here goes:

I don't see IC2/U2 on the Vero layout. Is the Vero an equivalent circuit to the schematic and operates the same without IC2?

EDIT:
I think I just had the "duh!" moment. The TL074 takes the place of the 2 TL072's. Correct?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 21, 2012, 03:26:07 PM
Quote
Why not cut down on op amp count and use the OTA for the envelope follower or expo current source? A FET could buffer the 4.5V reference just as well as the op amp circuit and you could maybe shrink the overall footprint of the design a bit.

Quote
There's also the two on-board darlington buffers that you could still put to some use.
Believe me, I tried to use both OTAs and darlingtons in many ways as I developed the circuit. But in the end I could not get the 'good behaviour' from an OTA rectifier or current source as I could from opamp versions, and whatever I did with the darlingtons they always ended up redundant, one way or another.

It certainly lends itself to a multi-band or stereo application. This small version is only the start! Hopefully some adventurous people will find the basic topology useful for their own compressor experiments!

EDIT:
I think I just had the "duh!" moment. The TL074 takes the place of the 2 TL072's. Correct?
Yep that's right. I wanted to keep the parts designators the same in the PCB and vero, but a quad opamp made for a smaller vero.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on April 21, 2012, 05:33:45 PM

[/quote]
Yep that's right. I wanted to keep the parts designators the same in the PCB and vero, but a quad opamp made for a smaller vero.
[/quote]

Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mike Burgundy on April 21, 2012, 07:05:53 PM
This small version is only the start! Hopefully some adventurous people will find the basic topology useful for their own compressor experiments!

Ooh, I know a glove in the face when I taste it! I just wish I had the time. I'm not even thinking about pretending I could come up with something like this on my own ;P
 Still haven't gotten around to building my last 2 projects beyond breadboard, and the first of those has been brewing for almost a year.... Any takers?

(edit: gotta learn to type slower, or more accurate)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Keppy on April 21, 2012, 08:10:43 PM
Nice! I've been looking forward to this one. Thank you!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bonaventura on April 21, 2012, 08:15:34 PM
understood. thanks cliff.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mr_deadmaxxx on April 22, 2012, 07:01:52 AM
 :D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: CaptainTuna on April 22, 2012, 12:52:02 PM
Great! Just great!
I am definitely gonna build this one next week.
Do you suggest any modification to it for using it with bass?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 22, 2012, 02:03:56 PM
Great! Just great!
I am definitely gonna build this one next week.
Do you suggest any modification to it for using it with bass?
It will work fine with bass right off the bat. You could increase the 100pF cap to 220pF if you like, which will reduce noise, since you don't need as much bandwidth.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: frank_p on April 22, 2012, 02:36:41 PM
Could someone do a little walk-trough of how the electronics works ?   ...please.  That would be great !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on April 23, 2012, 02:00:19 AM
> a little walk-trough of how the electronics works?

Very little walk:

This is all old-hat design. (What is new is getting it all to work nice under 9V supply.) You can find the general plan (over-complicated) in Crown and Peavey and other power amps.

(http://www.freewebs.com/valvewizard2/engineersthumbschem.jpg)

Signal goes in at U1a "+" and out at U1a "out".

Assume super-small signal, no limiting.

Assume U3a is essentially dead. (There is a teeny trickle through 1Meg to 4.5V.)

U1a gain is roughly 1Meg/10K (actually the 1Meg is varable and there's a 1K and a +1 in the formula). "Treble mod" brings in another 10K for double the treble gain.

Now put signal in. U1b is standard half-wave low-offset diode referenced to 4.5V. Negative signal peaks are captured on 1uFd cap. The peak voltage is forced by U2a onto a 1K resistor between a transistor and 4.5V. Transistor current varies from zero to 3mA.

This is why we need U2b, to hold "4.5V" steady despite 3mA thunks in transistor current.

Transistor current "wakes up" OTA U3a. It passes U1a output signal back to U1a input, in shunt with the 1Meg pot. This turns-down U1a gain, and thus the signal.

This is "backward" from the basic plans on OTA datasheets. Usually they run signal forward through the OTA, idle it at maximum current/gain, and reduce current/gain for limiting action. That works, good-enuff for many purposes, but isn't optimum. The high-current OTA has significant hiss, in part because the input is so very sensitive that most high-level signals must be attenuated before the OTA, and low-level signals necessarily get the same pre-attenuation. Also the turned-down OTA can be starved for headroom. In the backward connection, for super-small signals the OTA can be essentially "off", adding no hiss, and on strong signals the OTA current is rising so headroom is good. When limiting, input level to the OTA is essentially constant, and the designer can select this level on the OTA's THD plot so that distortion is small.

"Backward" connection would seem to need an additional op-amp. However in practice we always need to buffer the low impedance of the OTA attenuator (10K+220r) so it isn't more parts than the "basic" connection.

This design is feed-forward. It is easier to make a feedback limiter hold a constant level, but overshoot must be considered. A feedforward limiter needs very accurate rectifier and VCA to produce accurate limiting. It "can be shown" that both types can limit equvalently well, disregarding practical implementation details. In this case the OTA is a "perfect" VCA over more than the required range, and the rectifier is plenty accurate for the useful range of guitar signals.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: frank_p on April 23, 2012, 10:22:47 AM

It's great to have a small explanation in the same topic than the schematic is. Thanks Paul and Merlin.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mike Burgundy on May 08, 2012, 08:18:39 AM
This small version is only the start! Hopefully some adventurous people will find the basic topology useful for their own compressor experiments!

Ooh, I know a glove in the face when I taste it! I just wish I had the time.

I'm not picking up any gloves just yet, but if anyone's interested and wants to tinker, I just cobbled up a simple 3-band Linkwitz/Riley crossover that looks quite okay and can be used for multibanding. Just the schem simmed.
Yes, 3-band, will leave you with yet another unused half chip, I know... I just feel 2 bands won't quite cut it, and 4 is getting too complicated by far as far as knobs and board space is concerned. It's quite easy to extend this to 4-band, if needed. 4 bands might have the need for a 3-pole filter, which only needs an extra cap and resistor per opamp. Edit: actually that might not be as easy as it seems... 2-pole it is, I guess ;P

Lemme know, I'll put it up. Edit2: it's up.
Title: Schematic / PCB / layout
Post by: merlinb on May 16, 2012, 09:19:11 AM
Looks like my web page has run out of bandwidth, so I've added the files to photo bucket too. PCB, layout, schematic and everything is here:

http://s81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/

(http://i81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/engineersthumbschem.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cliff Schecht on May 29, 2012, 10:25:08 PM
Just knocked out a little SMD board for this compressor. The one thing I'm really interested in figuring out is how this compressor will compare to my beloved Orange Squeezer and the Dyna/Ross comps I'm building up as well (neither of which I've really ever used either). I've been using my OS for many years and enjoy the flaws that this circuit has. Makes for a very musical compressor, at least when running a guitar into an amp. I'm wondering if this compressor (the Engineers Thumb) will be too good and not the whacked out squishiness that the OS does so well. I'm curious to hear Merlin's thoughts on this, especially being that he is a EE as well and certainly knows the theory side of things. Perhaps this is why he chose the exponential current source over the simpler linear one for the OTA bias circuit..

I'm hoping to populate this board tonight. In my haste to finish the board quickly I of course forgot to mirror the transfer so I'll be flipping the SMD op amp and OTA over to salvage this board. For a board using 10 mil traces everywhere, this transfer came out too clean to just waste it! :icon_razz:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 29, 2012, 11:19:15 PM
> why he chose the exponential current source over the simpler linear

Thre's no exponential current source here.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on May 29, 2012, 11:52:50 PM
Just finished wiring this up after waiting a bit for the 13700 chip. I'm a bit of a comp affectionado, so it was nice to try out a new "easy" design. I hope it's okay to post my thoughts here:

Overall sound:
It sounds beautiful as a boost on certain milder compression settings.
In the stock setting, the most extreme compression settings lost some highs. The treble boost mod cures this, but I can see how players who use picks (I'm strictly fingers) might find this desirable.
The bass response is a little smeared at the most extreme comp settings.

How does the compression "feel"?:

The lowest ratio resistance provides no available boost, but it is extremely even limiting and feels very natural. The highs are fairly attenuated, so, again, I found the treble mod to be a perfect cure for my complaints here.

The next 100K of resistance was all very usable in every "normal" testing situation I messed with - it sounded right and reacted right at all areas of the sweep, but with varying levels of overall compression, high end, and boost available.

The compression is very natural compared to a Dynacomp (despite certain people's assumptions elsewhere), though I must admit that the range of the ratio knob for the purposes of compression can be fairly limited with any given guitar. Using my tele w/ broadcasters, anything above 250K was virtually indistinguishable from the settings below it except that I got more pumping like a mis-biased Orange Squeezer, and the release was a little too long when switching between slow soft notes and fast runs (meaning that the fast runs would keep a quiet part immediately following from sounding correctly); I tried a strat and found that the 100KA pot would suffice (but the low-input pickups did like the very top of the comp knob)! I  don't have a super high output guitar to test, so I ran a boost in front and I could see how, say, active pickups would like to have the 1M pot. It still had some transients and didn't distort (which is very nice), but there were some noise floor issues.

Mods?:
I built it almost stock - I used a 500KA pot for the ratio because that was more than sufficient with every guitar I own and gave me the most usable sweep. A 250KA would have been ideal for my purposes, but I didn't have one. After testing the attack mod (which I didn't like -- but then, I don't typically like that mod on anything) and the release mod (which I did like for more transparency, but the release is already very short), the treble mod was the only one I really found essential, as it cures the only problem I had with the highest compression setting.

Overall:

This walks the line between hard "effect" compressor boxes like the Orange Squeezer and Dynacomp and really transparent comps like the Flatline. It would certainly please people who want more squish than the optical comps but don't necessarily want to know if it's working.

I'd recommend this project to people looking for another "effect" comp, but maybe not people looking for absolute transparency.

Is is a "better compressor"? I think it's certainly better than the Ross for my tastes. I've never really liked the Ross. :P

One last thought:
It's tough on perf, and the etch is complicated with a lot of jumpers. Maybe a group buy for double-side fabbed boards is in order?

Anyway, it's going in a pretty green box as soon as I get to the drill press tomorrow.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cliff Schecht on May 30, 2012, 03:15:45 AM
> why he chose the exponential current source over the simpler linear

Thre's no exponential current source here.

Ah yes you are correct, the current source itself just produces an output current based on the input voltage. I guess the overall circuit could be considered exponential just in the sense that the charging and discharging of the caps happens exponentially, but the current source itself is linear. If his circuit acted in a truly linear nature the compressor might sound weird and probably unnatural to our ears. Or maybe it would sound cool? You could probably figure out a way to finagle one of the floating darlington pairs into a current source that forces the caps to charge linearly.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 09, 2012, 12:08:06 AM
Has anyone built the vero version yet?  I'm having a little trouble. I built it according to the vero on page 1 with the exception of a jumper to move the input (row 2) down to an unused row at the bottom. This places all of the leads going to the switch close together.

The signal switches between the board and bypass when I activate the DPDT switch, but the indicator LED stayed on in both conditions. While the switch was in bypass, I happened to turn the volume pot and the indicator dimmed of and on as I rotated the pot. While I was doing this, the volume pot started smoking.  I disconnected power, the switch and pots.

I reconnected just the power and the LED came on. I connected the "FS" and "Out" leads to simulate the switch in bypass and the LED stays lit. The other thing I noticed was there was 9v on the lead that goes to the center lug of the volume pot.

Q1: Is there supposed to be 9v on the center lug of the volume pot in bypass?  
Q2: Possibly a bad transistor?

Edit:  I'm using a tiny indicator LED (see photo below) instead of a standard 3mm or 5mm LED.
Q3: Could this LED's leakage be out of spec resulting in  the bypass circuit not operating properly?


Edit 2:  As my cousin Rosanne Rosanna Danna used to say, "Never mind...".  ;D  FS was soldered to the wrong track. I corrected it and now it turns off and on. Everyone else is in bed at this hour, so I'll test drive it tomorrow.


Here are some pics:

Vero layout:

(http://i1160.photobucket.com/albums/q485/jdansti/5b082bac.jpg)

My board:

(http://i1160.photobucket.com/albums/q485/jdansti/15263a83.jpg)
(http://i1160.photobucket.com/albums/q485/jdansti/b7f42b5f.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 09, 2012, 10:38:22 PM
Good news and bad news.

Good: Millenium bypass works fine. I get signal with effect on and in bypass.

Bad:  When the volume pot is at max and the ratio pot is at min (I assume 100% dry), the output volume is about 1/2 of the unbypassed volume. When the ratio pot is 100% wet, the output volume equals the bypassed volume, but there is no compression (actually, no compression on any settings).

Any ideas?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rousejeremy on June 09, 2012, 11:02:40 PM
Your Q1 looks backwards
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 10, 2012, 03:44:24 AM
Your Q1 looks backwards

Thanks for taking a look. I think the data sheet for the BC327 shows that Q1 is oriented the same as the vero layout.  Could you please look at the configuration below and let me know if you agree?

(http://i1160.photobucket.com/albums/q485/jdansti/7c8f3acf.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 10, 2012, 06:42:02 AM
I can't see any glaring errors, so I guess it's time to post your voltages. Also check the orientation of your diodes, since we can't see that in the photo.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rousejeremy on June 10, 2012, 11:20:06 AM
My mistake. I must have been looking at the pinout for a 2N pnp
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 10, 2012, 10:46:49 PM
Here are the voltages. I noticed that out of pins 1-8 on IC2, only pin 6 is connected to anything else.

PS 9.5

Q1
e 4.7
b 4.2
c 1.1

Q2
e 7.47
b 0 (LED turns off when I touch b with probe.)
c 9.5

IC1 
1.   4.7
2.   4.7
3.   3.2
4.   9.5
5.   2.4
6.   4.7
7.   4.7
8.   4.7
9.   4.7
10. 2.4
11.   0
12.  2.4
13.  4.7
14.  4.3

IC2
1.   0
2.   0
3.   0
4.   0
5.   0
6.   0
7.   0
8.   0
9.   0.01
10. 0
11.  9.5
12.  4.7
13.  4.7
14.  4.7
15.   0
16.  1.1

Here are the diodes:

(http://i1160.photobucket.com/albums/q485/jdansti/912fdbea.jpg)
(http://i1160.photobucket.com/albums/q485/jdansti/b6160016.jpg)
(http://i1160.photobucket.com/albums/q485/jdansti/163bae7c.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 11, 2012, 04:45:53 AM
Hmm, voltages check out.

Next step, check the wiring between the board and the off-board stuff (jacks / pots etc.)

EDIT: Aha! Double check R7- should be 10k but looks like 100R in your photo?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 11, 2012, 05:11:04 AM
Hmm, voltages check out.

Next step, check the wiring between the board and the off-board stuff (jacks / pots etc.)

EDIT: Aha! Double check R7- should be 10k but looks like 100R in your photo?

It sure looks like 100R! :icon_redface:  I'll take a look at the board as soon as I can get to it.  Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on June 12, 2012, 09:28:39 AM
Thanks for the eagle eye, Merlin!  I checked all of the resistors and found another wrong value. It works great now that I have the correct resistors in place!    :D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: The_Armadillo on June 20, 2012, 01:30:22 AM
So i build this little guy up, per the PDF with the PnP in it. I'm getting this nasty, gated distortion with the ratio anywhere above 9:00. Below there it cleans up significantly. Possibly a bad OTA? I got it on the cheap from eBay, so possibly a fake?
Only part subs were that I haven't put in the power filter cap, the output electro for a 1u poly.
I'll post voltages if the problem doesn't stick out.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on June 24, 2012, 11:52:48 PM
Hey, folks, I posted a video demo of this pedal on my YouTube. Hopefully it will convince some of the fence sitters to build this excellent pedal! :)

http://www.youtube.com/watch?v=n7VqdIlHkI0
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mth5044 on June 25, 2012, 03:36:13 AM
Has the VU'd, expanded edition come to fruition?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: StephenGiles on June 25, 2012, 10:32:45 AM
Hey, folks, I posted a video demo of this pedal on my YouTube. Hopefully it will convince some of the fence sitters to build this excellent pedal! :)

http://www.youtube.com/watch?v=n7VqdIlHkI0


Excellent demo, many thanks.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cliff Schecht on June 25, 2012, 03:31:09 PM
To be honest I have my doubts that any compressor will ever replace my Orange Squeezer. It's been one of my mainstays for so many years and is on 90% of the time during gigs. For what I want a comp to do, it's perfect.

I still need to build Merlin's circuit correctly. I've screwed it up twice now (bad perf build and etched a board backwards, neither worked :D) and really want to play with it still. I usually don't screw circuits up this badly when building but I've been pressed for building time between finishing up grad school and playing gigs. :-\


Also a comment on the LM13700: IIRC it doesn't have fantastic noise performance. You have to cut the signal down to the mV level at the inputs and then amplify the crap out of it again which in itself tends towards being noisy. Typically when I use a 13700 I try to keep the signal swings as large as possible before clipping to maximize noise performance. Merlins clever trick was to put the 13700 in the op amp feedback loop where the noise performance of the 13700 has a less significant contribution to the overall system noise (compared to if you were relying on the 13700 as a signal-path device).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on June 25, 2012, 09:21:25 PM
Also a comment on the LM13700: IIRC it doesn't have fantastic noise performance. You have to cut the signal down to the mV level at the inputs and then amplify the crap out of it again which in itself tends towards being noisy. Typically when I use a 13700 I try to keep the signal swings as large as possible before clipping to maximize noise performance. Merlins clever trick was to put the 13700 in the op amp feedback loop where the noise performance of the 13700 has a less significant contribution to the overall system noise (compared to if you were relying on the 13700 as a signal-path device).

Yes but compared to the CA3080 the noise performance is spectacular. I agree that it's not quiet like a TL074 or anything like that.

p.s. Re: Orange Squeezers, I'll see your 90% of the time and raise you 10%. ;) Always on during shows. I can't live without it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 26, 2012, 01:51:13 AM
> put the 13700 in the op amp feedback loop where the noise performance of the 13700 has a less significant contribution

Right: Dang near NO noise contribution when not limiting.

This can't be compared to "normal" use of OTA; in fact it is mostly the reverse  of OTA flaws. The hiss only happens in heavy limiting, and at that point who cares? As the note decays and gain rises, hiss gets _less_. I'm not going to work-out the idle noise because numbers don't mean much, and it is (should be) quick/easy to just try it. (No, I'm not giggling at your expense-- I do little PCB these days and you should have seen my 2-day screw-up of a simple 2-hour screen door last week.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 26, 2012, 04:10:55 AM
Hey, folks, I posted a video demo of this pedal on my YouTube. Hopefully it will convince some of the fence sitters to build this excellent pedal! :)                           http://www.youtube.com/watch?v=n7VqdIlHkI0

Great demo- you've done me proud! Also what's kinda spooky is that you bear more than a passing resemblance to me... (or perhaps I should say that I look rather like you :icon_redface:)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on August 22, 2012, 09:02:36 PM
I recently did a "fill this box" thread on Madbean's forum, offering a free PCB for anyone who told me what to fill a black box drilled with two pots and a toggle with. One poster suggested the Engineer's Thumb with treble boost not knowing I had already built one & how much I liked it ...

The trouble was, my previous layout was huge and long and skinny, and it wouldn't fit in the box I had. So that meant I had to come up with a new layout. I thought I'd share it with community for the perf lovers out there (or just guys who don't etch).

(http://jonpattonmusic.files.wordpress.com/2012/08/engineers-thumb.png?w=800)

VERIFIED 8/22/12 (I built it last night and tested it tonight.)

There are several jumpers -- it's just unavoidable with this circuit. So it's not the absolute cleanest circuit layout ever, but it's very compact for this build. There are no fully standing resistors or diodes, though a couple 1M and the 220R are squeezed onto 3 holes instead of 4. The board will fit with a battery in the case ... or even maybe even a charge pump daughter board for 18V if this circuit will allow it! I believe there are enough pads to accommodate adding the attack and release controls, though you may need series resistors to avoid weirdness.

PDF for those who want it: http://jonpattonmusic.files.wordpress.com/2012/08/engineers-thumb.pdf
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: batelfixx on August 25, 2012, 05:30:54 AM
Hi guys,

midwayfair has me inspirited.
I ´ve made a PCB. http://forum.musikding.de/cpg/thumbnails.php?album=619 (http://forum.musikding.de/cpg/thumbnails.php?album=619)
The numeration is like merlinb.
Tell me please if you find a mistake!  It´s one of my first!

Not verified!

Bastel

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 25, 2012, 09:20:31 AM

I ´ve made a PCB. http://forum.musikding.de/cpg/displayimage.php?album=lastup&cat=1&pos=0 (http://forum.musikding.de/cpg/displayimage.php?album=lastup&cat=1&pos=0)

I think that's the wrong link?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: batelfixx on August 25, 2012, 02:09:55 PM
Upps,  :icon_confused:

this is the old brain!
this are the pictures
(http://img4.imageshack.us/img4/5149/legender.jpg)
By batelfixx (http://profile.imageshack.us/user/batelfixx) at 2012-08-25
(http://img854.imageshack.us/img854/2701/bestckung2.jpg)
By batelfixx (http://profile.imageshack.us/user/batelfixx) at 2012-08-26
(http://img88.imageshack.us/img88/7105/52x40pcbprintable.jpg)
By batelfixx (http://profile.imageshack.us/user/batelfixx) at 2012-08-26
I hope now it is right - the preview will not go.
Modified on 2012-08-26
Bastel

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on August 25, 2012, 03:38:35 PM
nice job on the pcb! but the link is asking for a password
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on August 25, 2012, 07:23:33 PM
Hm. batelfixx, will that trace from R14 to the connection to Pin4 on IC3 print properly? You might have better luck putting R14 horizontally (keep the same top hole attacked to Pin 1 of IC2) and just connecting the other trace to the pads for R16/18. There's plenty of room between them and the PNP transistor pads. I don't etch, but I know that some people who do might not have a printer that can manage a good enough resolution for that trace.

Anyway, good job on it. It's by no means and easy circuit to do a layout for despite not having a particularly high parts count (took me four tries to get mine done).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on August 25, 2012, 09:33:52 PM
> will that trace from R14 to the connection to Pin4 on IC3 print properly?

Military/Industrial PCBs have been running traces between DIP pins since 1970 or before.

I think any modern PCB house can handle it fine.

It's too-tight for my Sharpie-mask techniques.... but I can always jumper it with scrap wire.

As you say, there's other ways to route this, and prolonged brain-pounding (or auto-route) could maybe neaten it a bit. But nothing looks "wrong" to me, and I've seen very sloppy layouts sound great.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: batelfixx on August 26, 2012, 03:56:04 AM
ok, midwayfair,
now the PCB more better to etch.
You can it use by copy and paste and print without scaling.

(http://img88.imageshack.us/img88/7105/52x40pcbprintable.jpg)
By batelfixx (http://profile.imageshack.us/user/batelfixx) at 2012-08-26

and new
(http://img854.imageshack.us/img854/2701/bestckung2.jpg)
By batelfixx (http://profile.imageshack.us/user/batelfixx) at 2012-08-26

I have no web-space to upload the pdf - sorry!
Bastel
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: batelfixx on August 27, 2012, 11:33:23 AM
... and now the link  -2. approach   ::)
http://dl.dropbox.com/u/100857549/Engineers%20thumb%20compressor.pdf
 (http://dl.dropbox.com/u/100857549/Engineers%20thumb%20compressor.pdf)
(Thanks, Jon)
Bastel
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kesh on August 31, 2012, 07:03:01 AM
(http://i81.photobucket.com/albums/j207/merlinblencowe/Engineers%20Thumb%20Compressor/CIMG7128.jpg)
I would dearly love to know what the jack sockets are that can be put in line with the foot switch. mine are always too big, even with dpdt
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 31, 2012, 09:18:51 AM
I would dearly love to know what the jack sockets are that can be put in line with the foot switch. mine are always too big, even with dpdt
I think they're all basically the same. They usually have a plastic bump on the end which I cut off with a sharp knife! There's a photo of what I mean here:
http://valvewizard.co.uk/makingpedals.pdf
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mth5044 on August 31, 2012, 04:43:57 PM
I would dearly love to know what the jack sockets are that can be put in line with the foot switch. mine are always too big, even with dpdt

Keep in mind, that is also a DPDT, not a 3PDT. It isn't as wide.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kesh on August 31, 2012, 05:06:23 PM

Keep in mind, that is also a DPDT, not a 3PDT. It isn't as wide.
yes, i can count to six
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mth5044 on August 31, 2012, 05:48:29 PM
Yikes, sorry for my concern.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on November 11, 2012, 11:40:21 AM
This weekend I learned that NE5532 won't work in EITHER the audio or power section. Although I don't understand why it won't work, I did find that 4558, LM358 and OPA2134PA (and TL062, obviously, though it's noisier in the audio path) DO work* as subs. What's going on here? I can't remember ever running into a situation where a 5532 wasn't a workable sub for a TL072.

*Of the OP amps that DO work, it seems to be really, really sensitive to the op amp, more than anything else I've run into. It vastly changes the compression character and decay. TL07x is clearly the absolute best and most natural sound, but it's weird that it's such a drastic change with some swaps.

Anyway, just thought I'd pass this on in case anyone else is in a bind with their chips and is looking for substitutes: Basically ... don't substitute in this circuit. :P
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 11, 2012, 11:57:40 AM
Quote
I can't remember ever running into a situation where a 5532 wasn't a workable sub for a TL072.

It's irresponsible of me to say this without recalling the specifics, but I've found a number of circuits where this is the case. Most recently, a BP filter I've been noodling with.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kesh on November 11, 2012, 12:29:26 PM
This weekend I learned that NE5532 won't work in EITHER the audio or power section. Although I don't understand why it won't work, I did find that 4558, LM358 and OPA2134PA (and TL062, obviously, though it's noisier in the audio path) DO work* as subs. What's going on here? I can't remember ever running into a situation where a 5532 wasn't a workable sub for a TL072.

*Of the OP amps that DO work, it seems to be really, really sensitive to the op amp, more than anything else I've run into. It vastly changes the compression character and decay. TL07x is clearly the absolute best and most natural sound, but it's weird that it's such a drastic change with some swaps.

Anyway, just thought I'd pass this on in case anyone else is in a bind with their chips and is looking for substitutes: Basically ... don't substitute in this circuit. :P
5532 is not the most stable of internally stabilised op amps, and also has very low input impedance, even for a bjt op-amp, and the 1M VRef resistors are way too high for it. As the biasing 1M resistor off U1b is also a threshold control, I can imagine the op-amp's input impedance is going to strongly affect the sound. Stick to fet input op-amps like TL072
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on November 11, 2012, 12:38:11 PM
This weekend I learned that NE5532 won't work in EITHER the audio or power section. Although I don't understand why it won't work, I did find that 4558, LM358 and OPA2134PA (and TL062, obviously, though it's noisier in the audio path) DO work* as subs. What's going on here? I can't remember ever running into a situation where a 5532 wasn't a workable sub for a TL072.

*Of the OP amps that DO work, it seems to be really, really sensitive to the op amp, more than anything else I've run into. It vastly changes the compression character and decay. TL07x is clearly the absolute best and most natural sound, but it's weird that it's such a drastic change with some swaps.

Anyway, just thought I'd pass this on in case anyone else is in a bind with their chips and is looking for substitutes: Basically ... don't substitute in this circuit. :P
5532 is not the most stable of internally stabilised op amps, and also has very low input impedance, even for a bjt op-amp, and the 1M VRef resistors are way too high for it. As the biasing 1M resistor off U1b is also a threshold control, I can imagine the op-amp's input impedance is going to strongly affect the sound. Stick to fet input op-amps like TL072

Yeah, I decided to do some light reading this morning after my post and didn't realize that the 5532 was BJT instead of FET (and obviously I can't just swap out a FET for a BJT all the time in a transistor circuit). Oh well. I'll just use a BB for now and swap it out for a 072 after my next parts order.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 11, 2012, 12:40:03 PM
According to the TI datasheet, the input resistance in a TLO7x is 10,000,000,000,000Ω, where as the input resistance of the NE5532 is 300,000Ω. Also, total supply current (for each amp) in a TL07x is 1.4 mA, in the NE5532 it's 8mA. The unity gain bandwidth of a TL07x is 3MHz, the NE5532 is 10MHz. Outside of input impedance, I don't have a clue if these things are connected to why it won't work in this case, but I noticed them glancing over the datasheets.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on November 11, 2012, 02:53:00 PM
The input impedance of the 5532 will be the main problem. It is too small compared with the release resistor which will cause the peak detector to go too far negative and overcompress. It will also cause the caps to discharge quite quickly, reducing the release time. The offset voltages will probably be quite large too, which may cause additional problems.
The 5532 isn't always better!  ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: sugonidamaso on January 27, 2013, 06:09:52 AM
Is it okay if I use 2n7000 instead of  BS170? Looking forward for your 5 knob version. Thanks in advance!  ;D
Title: Re: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: stevie1556 on January 27, 2013, 09:13:17 AM
I think I've got all the components for this build already (need to double check) so I'll attempt to get it built over the next few days. After I've finally finished my Spark Gap!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: R O Tiree on January 27, 2013, 07:11:18 PM
Does it have to be a BC327 for Q1? Or will a 2N3906 do?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on January 27, 2013, 07:53:28 PM
> Or will a 2N3906 do?

Yes.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: R O Tiree on January 27, 2013, 09:02:32 PM
Thanks, Paul. I had a good look at the datasheets and they look very similar indeed... thought I might have missed something.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on January 28, 2013, 01:30:10 AM
This part must have these specs or better:

Vbe @ 4mA under 1 Volt (typ 0.7V and reliable)
hFE over 10 (typ >100)
Vcbo over 4V (typ >20
leakage Ices under 1uA (typ <100nA)
fT over 1KHz (typ >100MHz)
or Tr under 0.1mS (typ <100nS)

You sorta can't buy a small PNP transistor this bad. Better is fine. Infine hFE is as good as hFE=25. More than 4V breakdown is fine (within limits, Vcb and hFE trade-off, a 4,000V BJT would have low hFE (but you can't find one)). There's no infinite fT but a GHz part is fine.

If you can tell NPN from PNP by smell (or tester) then you can rob old toys and appliances.

> BC327 ..Or will a 2N3906 do?

We all use the same parts but sold under different registries. In america, JEDEC "2N". In europe the "BC" numbering is common. Japan has the "2SC" etc system. Merlin is in England so his jellybean PNP is a BC. I use 2N2222 for everything, except PNP, so I try to remember which 2N390? is P-flavor. BOSS et al plans are full of 2SC parts. Very likely they all now come from one Chinese fab which puts the different numbers on as they are loading the ships to each corner of the world.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: earthtonesaudio on January 28, 2013, 08:31:39 AM
...If you can tell NPN from PNP by smell...

 :D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kipper4 on February 26, 2013, 05:16:16 PM
This is my next build. The lm13700 chip should arrive anyday now. Plus the BC327 too.
I have a few dumb questions. I just want to check i have it right in my head while at the planning stage rather than when populating the board.
(basics, I will be using perfboard not vero. I will be using 2 x TL072's. I havent as yet tried vero although it seems popular among builders here and i cant even contemplate etching my own boards at this point in my pedal building hobby)

Q1 do i attach all the points marked 4.5v to pin 7 of U2:B ( i'm using the schematic from the pdf of Merlin B's)
Q2 do all points marked 9V attach to the little arrow marked 9v in the top left hand corner of the power supply section of the board  or do they go to the point marked 9v at the end of link 2?
(i'm assuming its the power supply section because its seperate from the rest of the schematic and that seems to be the norn)

I do alot of assuming since i have no real education in EE. It's mostly served me well. Feel free to correct me and educate me please.
Oh and the other thing is i guess i dont need to include jumpers since i'm not using an etched board or vero.
Thanks for the help
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on February 26, 2013, 09:46:20 PM
Q1 do i attach all the points marked 4.5v to pin 7 of U2:B ( i'm using the schematic from the pdf of Merlin B's)
Q2 do all points marked 9V attach to the little arrow marked 9v in the top left hand corner of the power supply section of the board  or do they go to the point marked 9v at the end of link 2?
(i'm assuming its the power supply section because its seperate from the rest of the schematic and that seems to be the norn)

I do alot of assuming since i have no real education in EE. It's mostly served me well. Feel free to correct me and educate me please.
Oh and the other thing is i guess i dont need to include jumpers since i'm not using an etched board or vero.
Thanks for the help

You connect all points marked 4.5V ... together. You connect all the points marked 9v ... together.

You'll almost definitely need jumpers, but the reason the jumpers appear in Merlin's schematic is that he used Eagle (most likely) for the board layout, and you need to put jumpers in the layout for them to appear in the board layout.

If you want to save yourself some trouble of making the layout, my perfboard layout is a couple pages back.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kipper4 on February 27, 2013, 12:01:37 PM
And very good the perfboard layout is too.
As long as my colourblind eyes dont play tricks on me i should be ok with that.
Thanks again John.
Just for future referance though where are the voltage point. (just so i understand whats going on a bit better)
Thanks
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on March 03, 2013, 09:45:59 AM
Hey folks, I can't edit my post a while back. There was a mistake in my layout with the position of the cyan jumper. It didn't prevent the pedal from working, but I forgot that layout I posted was on my website and not my dropbox. Here's the updated/corrected perfboard layout. (If a mod sees this and they can edit the picture out of my previous post, that would be great.)

https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Engineer%27s%20Thumb.pdf
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 04, 2013, 05:54:15 AM
as a complete dumbass.. ::)

could someone put the 13700n's relevant pin numbers on the schemo please?..i'd like to bread it, and try those pot+switch mods too ;)

also is it better to use 2 dual op amps...or 1 quad?..hmmm... :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on March 04, 2013, 09:16:29 AM
could someone put the 13700n's relevant pin numbers on the schemo please?

They're in the build document file, the one that has the etching layout and bill of materials (http://www.freewebs.com/valvewizard2/engineersthumb.pdf).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 04, 2013, 09:24:04 AM
aha cheers man.....
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on March 04, 2013, 09:25:50 AM
could someone put the 13700n's relevant pin numbers on the schemo please?..i'd like to bread it, and try those pot+switch mods too ;)

Ah, I think Jon may have gone in there first.  This is the snippet I was going to suggest:

(http://www.bouron.org.uk/marc/ET13700.GIF)

(Or to use the "other" side of the 13700, read 16, 14, 13, 12 for 1, 3, 4, 5.)

Edit: two days away from a PC, and I gotta learn to type and mouse faster!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 04, 2013, 09:27:04 AM
thats the one...nice one!.. ;)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on March 04, 2013, 11:45:53 AM
Quote
also is it better to use 2 dual op amps...or 1 quad?..hmmm...

It's almost always easier to breadboard with two duals, IMO. Less jumping.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kipper4 on March 04, 2013, 11:49:57 AM
This is One fine compressor. It does a great job without being to squishy. Sure its noticable when it's on from bypassed.
I tried to make the 9v supply only switched on when the input jack is in. That didnt work.
The treble booster switch i will ammend next time to an on the board switch as John has done. So its optional when opening the box but to be honest i cant see me switching it off and on all the time.
I think this will be the first project i actually box up. I got my first 1590B at the weekend. I'll try to get a step drill this week.
Thanks Merlin for the excellant design.
Thanks to John and everyone else who helped guide me along the way and for all the guys who helped me debugg it too.
Next project.
millenium bypasses for my previous pedals and next future move on all project a protection diode in case of reverse polarity.

I really like the millenium bypass by the way. Are there anythings it wont work with?
Do you guys use it as a matter of course?
Is there a way of using millenium bypass with an input jack ground switch for use with batterys?


Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on March 04, 2013, 12:05:01 PM
Quote
I think this will be the first project i actually box up.

Quote
Next project. millenium bypasses for my previous pedals...

 ???

Quote
I really like the millenium bypass by the way... Do you guys use it as a matter of course?

Millenium bypass is fantastic. However, since its adoption, the once-expensive 3PDT foot switch is now relatively cheap, and judging by pictures on this forum, by far, the most common way we wire up true bypass with an LED indicator. There are ways to wire your pedals without true bypass that certainly have their own merits, but starting with a 3PDT is the way to go (common, easy, cheap).

There are many threads and examples of bypass wiring on this forum, but try using a search engine instead of the forum's built-in search function. Here's an example. (https://www.google.com/search?q=site%3Adiystompboxes.com+3PDT+wiring+ground+input+&aq=f&oq=site%3Adiystompboxes.com+3PDT+wiring+ground+input+&aqs=chrome.0.57j58.30285&sourceid=chrome&ie=UTF-8#hl=en&sclient=psy-ab&q=site:diystompboxes.com+3PDT+wiring&oq=site:diystompboxes.com+3PDT+wiring&gs_l=serp.3...12791.12791.0.12855.1.1.0.0.0.0.0.0..0.0.les%3B..0.0...1c.1.5.psy-ab.0MdJRQJGXCA&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&bvm=bv.43148975,d.b2I&fp=8b6e451abe7bae32&biw=1440&bih=762)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mike Burgundy on March 04, 2013, 12:14:02 PM

Is there a way of using millenium bypass with an input jack ground switch for use with batterys?

http://www.geofex.com/Article_Folders/Mill2extn/mil2plus.htm
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 05, 2013, 06:32:54 AM
okay, i numbered the pins, and lost the millenium too..and just made it easier on my eyes (which are pretty f.....d).....3pdt for me!..

just put this here for reference..(hope merlin doesn't mind my schemo tinker. :).)

i'll have a play around on breadboard later.. ;)

(https://dl.dropbox.com/u/7464107/engineersthumbschem22.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on March 05, 2013, 09:30:54 AM
I really like the millenium bypass by the way. Are there anythings it wont work with?

Anything where there isn't a DC route to ground from the output.  As an example, take a look at the Brian May Boost (http://www.geofex.com/images/BrianMayboost.jpg) at geofex.com.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kipper4 on March 05, 2013, 10:00:03 AM
Ok cool.
That's a shame that was my first from scratch build. I guess i'll just have to do true bypass on this one.
Is it still possible to put a resistor on the input to ground on this type of circuit then?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 05, 2013, 10:14:26 AM
@Rich it is there already..the 10M. :)


?..the junction of the emitter, and the 10k..

do both points (that junction) join and  go to pin 1 and 5?... ???


hold on, on jons layout he has pins 16/9/10.. and 6/7/8  joined..to ground.... ???

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 05, 2013, 10:52:22 AM
Is there a way of using millenium bypass with an input jack ground switch for use with batterys?

The Engineer's Thumb already does this, so it must be possible  ;)
See?
(http://valvewizard.co.uk/engineersthumbschem.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 05, 2013, 10:54:02 AM
Ok cool.
That's a shame that was my first from scratch build. I guess i'll just have to do true bypass on this one.
Is it still possible to put a resistor on the input to ground on this type of circuit then?

You can always use the Millennium bypass- just add a big resistor to ground if there isn't already one there.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on March 05, 2013, 11:19:32 AM

hold on, on jons layout he has pins 16/9/10.. and 6/7/8  joined..to ground.... ???


I grounded out the unused half of the LM13700.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kipper4 on March 05, 2013, 01:59:19 PM
Ok cool.
That's a shame that was my first from scratch build. I guess i'll just have to do true bypass on this one.
Is it still possible to put a resistor on the input to ground on this type of circuit then?


 i was talking about the treble booster here Astro. I could have made that more plain, Sorry

Fair points Merlin i missed that. I see it uses the +9v on the switch rather than the ground. When i did it the other way round the effect did nothing . Mind you i did have other issues, so i could have been those too.

I did ground out the unused bits on the lm 13700 as per johns Perf layout.

I struggled to make this fit in a 1590B box. I had to trim the circuit board as tight as i could go.
So i'm now rethinking my planning and circuit board maximum size. I need to rationalise space. How on earth John gets it in a 1590A i dont know. YET.
Title: Re: THE ENGINEER'S THUMB... Using The 13600?
Post by: smallbearelec on March 05, 2013, 07:50:41 PM
A guy wrote to me, said that he ordered the surface-mount 13700 from me for this build because that's all I had. I Do stock the NJM13600 in DIP, which Merlin says should work; the Engineer's Thumb does not use the output Darlington stage, and that's the only diff between those chips. If anyone has used the 13600 successfully, pls advise. I have offered to send one to my customer, and will advise hoiw that works out.

Regards
SD
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on March 06, 2013, 11:21:10 AM
Ok cool.
That's a shame that was my first from scratch build. I guess i'll just have to do true bypass on this one.
Is it still possible to put a resistor on the input to ground on this type of circuit then?

You can always use the Millennium bypass- just add a big resistor to ground if there isn't already one there.

Yep, which is is what I ended up doing on mine, once I'd worked out why it wasn't working!   :D   In fact, it was so bl00dy loud (according to my tame guitarist), that the second one I built (for his birthday) had a "convenient" volume pot at the output.

How on earth John gets it in a 1590A i dont know. YET.

Said this before, but I don't know how Jon gets all that handwriting in his 1590A builds!   ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on March 06, 2013, 11:20:59 PM
So i'm now rethinking my planning and circuit board maximum size. I need to rationalise space. How on earth John gets it in a 1590A i dont know. YET.

It involves some 1/8W resistors and an extra jumper to shave off a couple rows from my perfboard layout. Short electrolytics/tantalum/multilayer ceramic caps and all that jazz.

https://dl.dropbox.com/u/9878279/Jon%20Patton%27s%20layouts/Engineer%27s%20Thumb%20-%20Micro.pdf
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on March 07, 2013, 01:18:58 AM
What I'm most impressed with is how you guys fit this in a 1590A without making your own PCBs. Raw will.

Love this compressor by the way, thanks for sharing Merlin.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on March 07, 2013, 04:26:30 AM
i breadboarded this a few times yesterday but couldn't get the bugger going.... :-[

might give it another go today...2n3906 is ok for this i have read?..

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 07, 2013, 06:46:12 AM
might give it another go today...2n3906 is ok for this i have read?..

Yes, any PNP should work.
Title: Official 5-knob version of the Engineer's Thumb
Post by: merlinb on March 08, 2013, 12:27:28 PM
I have received a few questions about the ET recently, so I thought I'd post an official 5-knob version, in case there was any confuson about how to set things up:
(http://dl.dropbox.com/u/57831278/EngineersThumb5Knob.jpg)
(http://dl.dropbox.com/u/57831278/EngineersThumbRatio.bmp)
Title: Re: THE ENGINEER'S THUMB... Using The 13600?
Post by: KazooMan on March 08, 2013, 06:16:14 PM
A guy wrote to me, said that he ordered the surface-mount 13700 from me for this build because that's all I had. I Do stock the NJM13600 in DIP, which Merlin says should work; the Engineer's Thumb does not use the output Darlington stage, and that's the only diff between those chips. If anyone has used the 13600 successfully, pls advise. I have offered to send one to my customer, and will advise hoiw that works out.

Regards
SD

That would be me.  

I missed the 13600 when I was going through the parts list :(  

Added later, some of what I thought I wrote disappeared:  I have actually etched the board and populated it with the components I have.  I installed a socket for the 13600 chip that Steve has generously already sent me in the mail.  I have plans to attach "legs" to the surface mounted chip to get it into the socket.  I think that this will work since there are very few pins being used.  I have checked out wires for the job and found a bunch of resistors that I have which seat perfectly in the Mill-Max socket I am using. 

I should add that in looking at the pcb layout it looks like it could be modified to accept the surface mounted chip.


Note to Steve:  It would be great if you could somehow incorporate a way to search for ICs by the number without the initial letters.  I was looking to find LM13700 and only found the V13700M by scrolling through your entire inventory.  All bets are that there will be no discernible difference, but I will report back.  From looking at the pcb layout it looks like it would be possible to alter it to use the surface mount.

Geez... This was also lost in the original posting.  It would be GREAT if there was a way to search for chips with just the numbers and not the initial letter designations (manufacturers???).  (something like:  **number*).   An even better wish would be for a search that returned acceptable replacements!!!  ;D ;D ;D  I know that is too much to ask.  Thanks for supplying the parts that you do.  Small Bear is my Number One resource.

Oh, I should add that I have THREE shipments coming from Steve.  The original, the 13600 he offered to send me, and a few parts to repair a Dunlop Wah that I forgot to add to the original order.  I will be watching the mailbox eagerly!
Title: Re: Official 5-knob version of the Engineer's Thumb
Post by: deadastronaut on March 09, 2013, 05:37:04 AM
I have received a few questions about the ET recently, so I thought I'd post an official 5-knob version, in case there was any confuson about how to set things up:


thanks merlin...i'll breadboard this again.. :) ;)

are the leds important on this?..

i noticed that on this sche you have 10uf/1k..to level pot, but on the pdf schem its 1k/10uf....?
Title: Re: Official 5-knob version of the Engineer's Thumb
Post by: merlinb on March 09, 2013, 10:53:47 AM
are the leds important on this?..
They're not essential, but I would recommend them to avoid any really ugly distortion.

Quote
i noticed that on this schem you have 10uf/1k..to level pot, but on the pdf schem its 1k/10uf....?
They're in series, so it makes no difference either way! :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: earthtonesaudio on March 19, 2013, 10:20:12 PM
Merlin, check the input section of the bypass switch on your latest revision.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 20, 2013, 05:27:06 PM
Merlin, check the input section of the bypass switch on your latest revision.
Well spotted, thanks! Fixed now.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on March 21, 2013, 11:08:48 AM
Just wanted to give everyone a heads-up: Jacob Kokura just released a PCB of the Thumb using the 3080 chip in place of the LM13700:
jmkpcbs.com/JMK_PCBs/Store.html

(I'm not affiliated.)

It's a very nice, clean looking layout; I can't comment on any sound differences between the two chips as I haven't built it that way yet, but Jacob has said that he couldn't hear an appreciable difference.

I thought this might be of interest to the folks that don't etch or do vero/perfboard.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Tubebass on March 21, 2013, 12:05:27 PM
I used a 13600 in my build. Although I don't have it boxed yet, bench testing confirms that it does work fine.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: KazooMan on April 02, 2013, 06:41:05 PM
Well, I am finally back with my comparison.  It sure took a while.  It all came down to a very sharp utility knife, a trip to the ER, eleven stiches in my hand, and waiting for it to heal enough so I could get the stupid bulky bandage off.  The hand will be just fine.  The woodworker's ego is still having a few issues.

I completed the build of the pcb version and used sockets for the chips so I could compare the NJM13600 chip that Steve sent to me with the surface-mount LM13700 I purchased from him at Smallbear.  This was my first attempt at a pedal in this size enclosure and that brought its own issues to bear.  I did incorporate the two protection leds to minimize distortion, I used a trimpot to replace the resistor to have the threshold capability, and I temporarily added a switch to control the treble boost.

First off, the 13600 IC did work as anticipated.  I tried the treble boost switch here and did not find a lot of difference.  As has been discussed, the threshold trimpot is not really that useful over just the release pot.  I really like the compression and especially the sustain.  However, there was quite a noticable amount of distortion at higher settings of the release control and the pedal reduced the output to the extent that I had to have the level pot at about 80+ % to equal the bypass level.

I tried to solder some leads to the legs of the surface-mount IC with the expected negative results.  I decided I had to make a mini pcb to mount the board and provide contacts for regular leads (not many leads are required).  My first attempt at this involved running leads from this board to the sockets of a millmax socket.  I built it, epoxied it all together and had my own chip ready to plug in.  It worked great, but it was too thick with the other socket already in place and I couldn't get the bottom of the box on :(

I made another pcb with the LM13700 and just bent the leads into the desired locations (using a socket for alignment) and then applied some epoxy.  The resulting "chip" worked just fine!

These are subjective "ears only" comparisons at this point.  The REAL LM13700 improved the level issue.  I know that this is true from AB comparisons with the pots held constant.  The distortion issue seems much better with the 13700.  I really need to explore this with my oscilloscope to see if my ears are fooling me or not.  I had removed the treble boost switch so I cannot report on that. 

I may have a go at modifying the pcb layout to incorporate the surface mounted chip.  This will not be trivial since all of the connections are mirror images and there are already several traces running under the chip. 

Here's a quickie photo of the Rube Goldberg IC chip in the pedal.  The picture gives some funny color cast to the solder joints.  It is not there in the real pedal.

(http://i50.tinypic.com/4uaond.jpg)

Oh yeh... I should add that the reason the 47 uf cap is laying on its side is that some dummy cut the notch for the DC plug on the wrong side of the box.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on April 18, 2013, 02:52:17 PM
I built another one. This one also has a gain reduction meter of sorts, and a pregain stage with active treble boost/tone control, making it probably the quietest 9V compressor you can lay your hands on. It was also my first attempt at acrylic flow technique (aka swirl painting). Annoyingly, the lacquer seems to have reacted somehow and caused some grey speckling n the top right... :-\
(https://dl.dropboxusercontent.com/u/57831278/ET_GTI_small.jpg)
(https://dl.dropboxusercontent.com/u/57831278/CIMG7656small.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Chugs on April 18, 2013, 04:07:05 PM
Cool. How did you implement the treble boost/tone control?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on April 21, 2013, 05:51:41 PM
looks great merlin: 8)


ok, i decided to give it another go on breadboard and its working now, with the leds on input too..

but its very distorted/broken up?...especially with the sustain right up....or even halfway....i'm guessing this isn't normal right?. ::)

should i ground all unused pins of the 13700n?.

cheers rob.



Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on April 22, 2013, 02:02:28 AM
Quote
should i ground all unused pins of the 13700n?

Based on my experience breadboarding and building this, it shouldn't be distorted, nor should you have to ground the inputs.

I believe certain circuit's inputs are grounded because they can oscillate or amplify other noises that end up in your signal somehow, not because they actually alter the other op amps or inverters or what-have-you within the same IC.

Do you have a few ICs to swap out? They'll fry out with too much current going to the amp bias input pins.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on April 22, 2013, 03:44:47 AM
cheers gary,

yep i have a couple i'll have a swap... ;)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on April 22, 2013, 09:34:43 AM
cheers gary,

yep i have a couple i'll have a swap... ;)

Make sure you aren't using something besides a TL072. Most any BJT-based op amp will distort like crazy. It has to be a FET-based OP amp.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on April 23, 2013, 06:07:13 AM
ok swapped the 13700n..

and have 2x tl072's...

i'm using 2n3906,  /  2x5mm red leds.../ 1n4148's

i took the 13700n off my mutron breadboard so i know its fine.

still distorting... ???


edit:  when i strum the guitar hard the sounds dips to nothing, then swells back up...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on April 23, 2013, 08:56:31 AM
Rob: Post pics and voltages.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Neurowork on May 14, 2013, 05:12:11 PM
Hi,

First of, many thanks to Merlinb for this great design.
I was going to build the 2 knobs version when he posted the 5 knobs version with the bright switch so I figure ... let's give it a try.

I made a neat 2 layers prototype board layout I'm sending to the fab today.

(http://uploads.oshpark.com/uploads/project/top_image/fODR9jH0/i.png)

It is 2" wide which means it'll fit in a 1590B.
I'll have 2 spare boards if anyone's interested.

Can't wait to populate and rock this baby.

Cheers.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mth5044 on May 14, 2013, 05:33:51 PM
^Awesome layout!

@Merlin - what chip/circuit did you use for the LED meter? Looks SO COOL
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: TheWinterSnow on May 16, 2013, 12:47:49 AM
I am curious about a small mod to the design.  Since I don't have much knowledge in OTAs but was wondering if the circuit could be adapted to a +/-9v supply by swapping the original ground to -9v, the original Vref to ground and well 9v to 9v.  If not, are there simple modifications to the circuit that could make it compatible.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on May 16, 2013, 04:30:54 AM
I am curious about a small mod to the design.  Since I don't have much knowledge in OTAs but was wondering if the circuit could be adapted to a +/-9v supply by swapping the original ground to -9v, the original Vref to ground and well 9v to 9v.  If not, are there simple modifications to the circuit that could make it compatible.

I was wondering the same thing recently - http://www.diystompboxes.com/smfforum/index.php?topic=102280.msg906530#msg906530 (http://www.diystompboxes.com/smfforum/index.php?topic=102280.msg906530#msg906530)
In summary, it is not as trivial as it sounds.
Title: Re: Re: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: stevie1556 on May 16, 2013, 06:48:58 PM
Neurowork - is your design for a 3PDT switch layout or for the millennium bypass as per the original? If it's for a 3PDT I'll be interested in a board if there is still one free, just let me know the cost with postage.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Neurowork on May 17, 2013, 05:13:12 AM
3PDT ;)
I have a big stack of 3PDTs in my stash so I ditched the millennium bypass.
I have one board left. PM me if you're interrested.
Title: Re: Re: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 17, 2013, 08:15:59 AM
Neurowork - is your design for a 3PDT switch layout or for the millennium bypass as per the original? If it's for a 3PDT I'll be interested in a board if there is still one free, just let me know the cost with postage.

You do realise that you can still use a 3PDT even if the board has Millennium Bypass on it, right? I don't want anyone to think that providing the facility for Millennium bypass somehow prevents you from using a 3PDT if you prefer. Nothing ever stops you from using 3PDT, whatever the circuit.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Neurowork on May 18, 2013, 05:34:30 PM
I do absolutely. I just removed the millennium bypass to lower the part count :)

Thanks again for the great schematics merlinb! My board are still in the fab but I can't wait.

Cheers!

Edit : Just realized the previous message was not for my benefit. Got to put the soldering iron down and hit the bed !!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on June 05, 2013, 02:31:31 PM
@ Neurowork
 Maybe a pic of the copper below layout can do me a lot of help  ;D

Thank you
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 05, 2013, 06:13:31 PM
just wanna say i built the 5-knob version of this a coupla weeks back, and now i hardly jam without it. you've no doubt heard it a million times, but awesome work, Merlin! funnily enough, a coupla days after making it, i was asked to fix (what i think was) a Ross clone from the early 80's - crackly pot - and the ET just felt that little bit more transparent and was much more tweakable.

at the moment it's in an old mains transformer block of all things, strangled by electrical tape, but i plan to transfer it to a more sturdy enclosure at some point. the only issues i have are some weird clicking when bypassed that varies with the ratio control (although i attribute this to me jamming the input, output, DPDT and separate Millennium board [used Sabrotone layout] untidily into to small a space), and it starts to squeal when Release is at 0. i'm not too bothered by that, though. just hope i don't ruin it when i change enclosure because i would really love to use this thing live.

any ideas on the range of each setting in milliseconds etc., that might help with future labelling (or just adjustment generally)?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Giglawyer on June 05, 2013, 08:47:52 PM
Are there any more PCBs available for this? I would love to build a five knob one.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 26, 2013, 06:51:23 PM
i'm kinda bored but low on parts - anyone have an idea if you could use a simple comparator to make a compression indicator? nothing fancy, not actual compression amount or anything. currently probing pins and hitting stings to see what voltages i could compare.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 27, 2013, 08:38:26 AM
i'm kinda bored but low on parts - anyone have an idea if you could use a simple comparator to make a compression indicator? nothing fancy, not actual compression amount or anything. currently probing pins and hitting stings to see what voltages i could compare.

One way would be to compare the voltage on the base of the PNP transistor with a fixed voltage (about 4V). When it starts compressing, the base voltage will drop below 4V.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 27, 2013, 04:41:59 PM
One way would be to compare the voltage on the base of the PNP transistor with a fixed voltage (about 4V). When it starts compressing, the base voltage will drop below 4V.

sweet, cheers! i'll look into that. would there be any way to make the bias variable by input level or is it just not feasible in this case? and would the circuit be loaded down at all by tapping the PNP?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 27, 2013, 05:34:27 PM
sweet, cheers! i'll look into that. would there be any way to make the bias variable by input level
Not sure what you mean...

Quote
would the circuit be loaded down at all by tapping the PNP?
Its driven by an opamp so it should be OK with loads down to a couple of k-ohms.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 27, 2013, 06:35:07 PM
i mean would it be possible to only light up when played (and compressed, ofc)? i tried what you suggested (with a voltage divider to get as close to the PNP base voltage with threshold/ratio both fully-off) and the light would go on and stay on when the threshold pot was turned past a certain point. so i'm probing around for a source to take the pre-compressed signal from to use that as Vref.
maybe i could somehow use an NPN or an LM386 or something (either with or without a comparator) to accomplish this & maybe even get ratio-dependent brightness too?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 27, 2013, 07:01:22 PM
how bout this?

(http://i.imgur.com/0Xr2r5z.png)

Edit: i actually built this and it kinda works! it's imperfect for now, i probably screwed something(s) up, but at this intoxicated, late hour it seems that the intensity and/or sensitivity of the light is affected by the Threshold pot. it seems to just stay on dimly when it's at 0, which ofc isn't ideal because it doesn't really represent 0 compression, but it doesn't respond at all to playing when in that state which is good i guess. i appear to have an issue where the reference voltage goes up the same as the comparison voltage, prolly symptomatic of a solder bridge although i can't see one (yet).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on June 27, 2013, 10:53:13 PM
Merlin B,
How is it doing with 5 knobs so far ?
Is it a worth-it-to-try mod or maybe a 3 knobs is sufficient enough ?
Would u be so kind to share the 2 layer 5 knobs PCB layout here ? Thank you in advance.  ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 28, 2013, 06:03:29 AM
Would u be so kind to share the 2 layer 5 knobs PCB layout here ? Thank you in advance.  ;D
Here you go, a single-sided version:
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf

Quote
i mean would it be possible to only light up when played (and compressed, ofc)? i tried what you suggested (with a voltage divider to get as close to the PNP base voltage with threshold/ratio both fully-off) and the light would go on and stay on when the threshold pot was turned past a certain point.
The base voltage is proportional to the compression, so if the circuit is working properly you only have to compare this voltage with a fixed reference and the LED will switch on only during compression. If you have it on breadboard or something, then you may simply be picking up hum, which is being compressed, causing the LED to be on permanently...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 28, 2013, 09:05:25 AM
The base voltage is proportional to the compression, so if the circuit is working properly you only have to compare this voltage with a fixed reference and the LED will switch on only during compression. If you have it on breadboard or something, then you may simply be picking up hum, which is being compressed, causing the LED to be on permanently...

that's good news, less hassle lol. it's set up in the enclosure itself (cover off), but definitely full of imperfections as yet. i spent 13 hours straight trying an ADA Flanger the other week and it made me think there must be a plottable curve for time spent:available brain power ratio, as i made a few errors despite what i thought was triple-checking lol. maybe i could put in diodes to get the right forward voltage so the light comes on all staccato-like and pseudo-advanced.

while we're at it, any idea why my build squeals at 0 Release time? different problem probably, but coincidentally also related to a pot at min. resistance. thanks for all the help so far!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 28, 2013, 11:10:52 AM
while we're at it, any idea why my build squeals at 0 Release time? different problem probably, but coincidentally also related to a pot at min. resistance. thanks for all the help so far!

What component values are you using for the release pot and series resistor? Maybe they're too small.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on June 29, 2013, 10:45:12 AM
i'm pretty sure i followed the BOM here to a tee http://www.sabrotone.com/wp-content/uploads/2012/05/EngineersThumb.gif (http://www.sabrotone.com/wp-content/uploads/2012/05/EngineersThumb.gif),
 so a 1M linear for release pot.

i'll have to fix an issue i've created from too much tinkering - now when i turn the Ratio up just a little bit it clicks into just a fuzzy kinda distortion. could be the BC327 as i was hastily soldering around that, but i'll fix that before trying anything else.

i rebuilt the compressor light circuit to make it less "experimental", the comparator stage worked (trimpot to match bias to transistor base), and everything on the LM386 worked bar the output for some reason. even with the 10uF 200x gain setting the output was too low to light up. worked with the first attempt though so i've probably screwed something up
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on June 30, 2013, 01:39:45 AM
Would u be so kind to share the 2 layer 5 knobs PCB layout here ? Thank you in advance.  ;D
Here you go, a single-sided version:
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf

What a superb sharing, Merlin B !
Awesome job, man. Thank you.  :)
I'll work on this asap.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 30, 2013, 04:48:16 AM
the LM386 worked bar the output for some reason. even with the 10uF 200x gain setting the output was too low to light up.

I would have thought the LM386 is overkill for this application; an ordinary opamp could do the job. :icon_neutral:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on July 04, 2013, 11:01:56 PM
I have a few questions...

1. So this PCB has measurement 115 x 60 mm from edge to edge of the width and height precisely ?
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp

2. How do i eliminate the LED bar graph, coz it's hard to find/buy one here ?

Thank you
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on July 05, 2013, 04:54:52 AM
1. So this PCB has measurement 115 x 60 mm from edge to edge of the width and height precisely ?
Yes. I always try to use round numbers when designing a board!

Quote
2. How do i eliminate the LED bar graph, coz it's hard to find/buy one here ?
The bar graph is just ten LEDs packaged in a solid plastic block. You can use ordinary LEDs instead, wired up to the same pads, like this:
(http://i81.photobucket.com/albums/j207/merlinblencowe/sd_zpsd1a9e451.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on July 05, 2013, 04:58:37 AM
Woo hooo super awesome !  :icon_idea: :icon_biggrin:
Let me try, let me try ......hahaha....
Thank you so much, Merlin B
Title: Re: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: sugonidamaso on July 05, 2013, 06:27:21 AM
Thank you so much for this! Is there a pcb for a 1590b series?without led block? :-[ too much to ask but thank u in advance.
Title: Re: Re: Re: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: sugonidamaso on July 05, 2013, 06:27:57 AM
Thank you so much for this! Is there a pcb for a 1590b series?without led block? :-[ too much to ask but thank u in advance!

double post sorry.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 17, 2013, 10:24:19 AM
take a feed from Pin 7 of IC2 (the opamp connecting to the PNP), hook it up to the Base of a NPN, and wire V+ through the Collector and LED from the Emitter for a simple-yet-handy compression indicator. score!

just re-read my last posts, a power amp IC does seem like overkill in hindsight.

my aforementioned distortion was caused by the board shorting against the treble switch. really is the most obvious stuff sometimes.
now to fix that damn ticking when it's bypassed.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on July 17, 2013, 10:39:06 AM
take a feed from Pin 7 of IC2 (the opamp connecting to the PNP), hook it up to the Base of a NPN, and wire V+ through the Collector and LED from the Emitter for a simple-yet-handy compression indicator. score!

just re-read my last posts, a power amp IC does seem like overkill in hindsight.

my aforementioned distortion was caused by the board shorting against the treble switch. really is the most obvious stuff sometimes.
now to fix that damn ticking when it's bypassed.

Sweet, I might add this to one of my builds. :)

I bet if you stuck a green LED on there, you could have two levels of indication. (Blue might be overkill ...)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 17, 2013, 11:26:14 AM
i used a white LED as they're all i have lying around, seems to work ok. would be cool to have another light for pre-compression level but i'm just trying to fill holes in a repurposed enclosure lol.
i think i used a BC183 although i might've swapped it out for a 2n5088. id imagine either would work, though

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: earthtonesaudio on July 17, 2013, 12:39:17 PM
how bout this?
(http://i.imgur.com/0Xr2r5z.png)

This circuit is an unusual choice.  Let me explain why I would do it differently:

First, a quirk of the lm386: its output biases to 1/2 of its supply when its inputs are the same.  Another quirk is that its inputs are ground-referenced by internal 50k resistors, so your circuit as drawn would work the same with nothing connected to the lm386 inputs.

Next, your comparator is supplying power (or not) to the lm386, based on what happens at the NPN base.  This means if the NPN base goes below 4.36V, the comparator output will go high (ideally 9V but the device will drop some voltage so probably more like 8V).  This means the lm386 output will go to about 4V and light the LED.

Last, each active device (tl072, lm386) has some internal resistance so this adds in series and provides some (unknown) current limiting to the LED.  You could estimate/calculate this effective resistance by taking the output resistance of the tl072 plus that of the lm386.

I would suggest a series limiting resistor between the tl072 and LED to limit the current to whatever the LED's max is (typically 20ma) and ditch the lm386 for this application.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ark Angel HFB on July 17, 2013, 03:37:14 PM
I'm jumping into this cold and have not read the thread yet...

Do say it I plan to read after posting if I find my answer I will remove this..

The Keeley comp was based on the Ross... how does this stack up to it?

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on July 17, 2013, 05:11:40 PM
The Keeley comp was based on the Ross... how does this stack up to it?



Pretty sure merlin touts the advantages in the first post. :/

Main things are quieter, feed forward, and more range of compression (both less and more).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 18, 2013, 10:34:18 AM
hmm, from what i grasp, the LM386 solution was not only at risk of being inaccurate, but borderline-unusable, Alex. thanks for the explanation, hopefully someone in future will persevere with using a comparator and heed that advice instead of just lazily resorting to a bare NPN like i did.

for the record, the NPN-powered dimming compression light i now have is pretty handy for something so simple! even seems to respond to Attack & Release. now i just need another compressor so i can switch between rhythm and lead...

The Keeley comp was based on the Ross... how does this stack up to it?

i know it's not quite what you asked, but i replaced a pot for someone on a Ross clone soon after building this comp, and that just seemed ham-fisted and noisier in comparison to the ET. that's probably subjective.
Title: Compression indicator?
Post by: merlinb on July 18, 2013, 11:16:01 AM
for the record, the NPN-powered dimming compression light i now have is pretty handy for something so simple!

I'm lost- what did you end up using?

I haven't tried it, but I would have thought this would work. Depends if the 4.5V buffer can supply the LED current or not . The 470R resistor might also need tweaking for the best brightness range. If anyone tries it, do let me know if it works!
(http://i81.photobucket.com/albums/j207/merlinblencowe/CompIndicator_zps5153446f.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 18, 2013, 11:54:55 AM

I'm lost- what did you end up using?


if i understand the original schematic right (which i probably don't), i'm doing pretty much what you've just described. not sure if this can be considered an accurate indicator of the output itself, as there's still some stuff taking place after, but it does respond to the settings used in what seems to be a surprisingly functional manner. only difference in my setup is that i'm using 9V+ separately instead of vbias, because i'm lazy

off-topic kinda, but as i'm pressed for real-estate in this enclosure, i'm thinking of just making the pedal always-on and using the former bypass DPDT to switch a resistor in & out of the Release pot wire to alleviate a lead/rhythm disparity i noticed at band practice last night. i'm thinking of putting something between 220k-470k connecting to lug 1 of the Release pot. not sure if i should replace the pot with a 500k or not, else the total resistance could exceed 1M. would that be bad?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on July 18, 2013, 02:12:45 PM
i'm thinking of putting something between 220k-470k connecting to lug 1 of the Release pot. not sure if i should replace the pot with a 500k or not, else the total resistance could exceed 1M. would that be bad?
Should be fine.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 18, 2013, 04:36:17 PM
works! i put 320K on one path for handy lead switching. might need a little bit more, but i was hesitant to jump straight to 470k. got an LED ground connected to the spare pins of the DPDT. thanks for the reassurance, Merlin.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ark Angel HFB on July 18, 2013, 11:49:09 PM
i know it's not quite what you asked, but i replaced a pot for someone on a Ross clone soon after building this comp, and that just seemed ham-fisted and noisier in comparison to the ET. that's probably subjective.

Naa man that is exactly what I needed to hear. The first post talks about the dynacomp not the Keeley and well... yeah.

I guess I'll give this one a shot... >_> too bad I ordered a bunch of chips for teh Keeley already... looks like I'll take a day and churn out some clones for buddies at cost so I can try this one.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 19, 2013, 01:23:00 AM

I guess I'll give this one a shot... >_> too bad I ordered a bunch of chips for teh Keeley already...

if you mean the CA3080, then you're in luck. this layout uses that instead of the LM13700: http://tagboardeffects.blogspot.co.uk/2012/11/engineers-thumb.html (http://tagboardeffects.blogspot.co.uk/2012/11/engineers-thumb.html), but you could probably use a daughterboard to use it on another/your own layout. Engineer's Thumb only uses one half of the 13700 anyway.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ark Angel HFB on July 19, 2013, 02:25:47 AM

I guess I'll give this one a shot... >_> too bad I ordered a bunch of chips for teh Keeley already...

if you mean the CA3080, then you're in luck. this layout uses that instead of the LM13700: http://tagboardeffects.blogspot.co.uk/2012/11/engineers-thumb.html (http://tagboardeffects.blogspot.co.uk/2012/11/engineers-thumb.html), but you could probably use a daughterboard to use it on another/your own layout. Engineer's Thumb only uses one half of the 13700 anyway.

Yes I'd seen that... To be honest I thought that the ET was a Keeley clone at first with a few tweaks... a bad assumption I'm learning... Still since I already have the circuit for one Keeley done... I think I'll box it up and Box up the ET and do an honest vid showing off both side by side as a fair comp for anyone else. ^_^

Also I'll redo the Vero and try and make it a bit more space saving and add in the extra control options... for those of us that find etch to be weird scary voodoo magic of the Gods...

A fire ant just bit my foot... @#%$ @#$% @#%$.
Title: JMK 3080 PCB
Post by: merlinb on July 19, 2013, 03:50:40 AM
Naa man that is exactly what I needed to hear. The first post talks about the dynacomp not the Keeley and well... yeah.
The Keeley and Ross are identical to the original Dynacomp. They're all the same pedal. The Keeley and Ross are just knock-offs with a couple of resistors changed, which apparently justifies the higher prices and general hype. (OK, the Keeley also has an attack control added, big wow... ::))

When I designed the ET, the whole point was to make sure it could do everything the Dyna/ROss/Keeley can do, and more and better and cheaper! :)

Quote
I guess I'll give this one a shot... >_> too bad I ordered a bunch of chips for the Keeley already... looks like I'll take a day and churn out some clones for buddies at cost so I can try this one.
JMK does a PCB for the ET that uses a 3080.
http://www.jmkpcbs.com/JMK_PCBs/Store
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: psychedelicfish on July 19, 2013, 05:38:41 AM
I've made a PCB layout (https://www.dropbox.com/sh/4pgodcylxnvr4iq/xyENhOC8sy/ETComp.pdf) for the ET, using a bipolar supply. I will use this in a multi-effects box that I will eventually build. I've checked it for errors myself, but if you can spot any, please point them out.
Thanks,
Edward
Title: Re: JMK 3080 PCB
Post by: MrStab on July 19, 2013, 09:15:42 AM
When I designed the ET, the whole point was to make sure it could do everything the Dyna/ROss/Keeley can do, and more and better and cheaper! :)


word. my omission of any kind of on/off switch says it all. lol
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on July 19, 2013, 12:56:25 PM
getting that weird ticking this time when the effect is on, the compression level light flickers along with it. seems variable, as i lightly kicked it a coupla times and it disappeared lol. can't see how it'd be a short, though. there's a 470uF to ground after the V+ splits off to the NPN from past experimentation (covered the damn thing in hot glue so can't easily get a 100nF from ground), maybe i should try decoupling the main circuit itself. using an adaptor with at least 1A current available.

Edit: decoupling the board itself did nothing.
Title: Re: JMK 3080 PCB
Post by: Ark Angel HFB on July 19, 2013, 03:02:36 PM
Which apparently justifies the higher prices and general hype.
Quote

I'm Kinda a one man pedal company making stuff for all my buddies and selling the extra on ebay to make rent... and how the big companies mark up there stuff kinda ticks me off... When you know they buy in bulk... and you know they make them fast... The total pedal cost in parts can't be more than $20 and yet they are selling them for $260... I mean it makes the bank account happy but damn... I'd rather work a little harder price my stuff at like $70 or $80, and have dudes with three of my pedals on their boards than just one...

Maybe I'm crazy it is just that I'm sick of the stupid notion you have to spend a mounts wages to buy two pedals... great tone is cheap... Companies are just holding it hostage...

When I designed the ET, the whole point was to make sure it could do everything the Dyna/ROss/Keeley can do, and more and better and cheaper! :)
Quote

Thanks for setting me straight man... I'm still learning this stuff. I can design veros from circuits easy, but I'm not on your guys level of knowledge yet about which pedals are clones of others. Still... I'm starting to get the same hype feeling from this as I did with the Valvecaster... a really great pedal that everyone on here can get behind and make the new standard.

I think this project will be the one that inspires me to take the step into etching... what bold new world lays ahead. XD
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: ketterman on July 27, 2013, 08:38:29 AM
I understand doing things like this for the love of the game, but Merlin, you should be getting paid for this. I bought both of your books. Perhaps that counts for something.
I breadboarded the project last night and it definitely delivers on the 'better compressor' description!
Now to decide which options go into the final enclosure...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 09, 2013, 04:29:05 PM
Hi,
I've bread boarded the original circuit and I think this is a great compressor. So I decided to build your second version with a VU meter exactly as you describe in the GTI documentation, Merlin.

The compressor itself works great in all areas but I can't get any kind of response from the 10 segment LED. It flickers when I plug in the power, which is encouraging.

Any ideas where I should start looking? I know the VU signal is taken from Q1 but I'm pretty lost after that.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 14, 2013, 04:32:22 PM
Deleted for stupidity...  :icon_rolleyes:

All fixed - apparently I have difficulty distinguishing red from brown...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on August 15, 2013, 11:36:02 PM
> stupidity...  I have difficulty distinguishing red from brown...

NOT stupid!!

There is color-blindness, though you'd probably have a clue by now. (There's online tests which can say "No" or "maybe".)

Mostly some reds and some browns are not much different.

Especially in crappy light.

I have to be very fussy about the light at my resistor bench. When I had skylights, that was great. A good 100W *incandescent* is tolerable. Some fluorescents (including compacts) have such a narrow peak of "red" that all the colors near there look alike.

And part of our self-education includes learning our "favorite mistakes", so when we go "? ? ?" they come to the front of the list of things-to-check.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: psychedelicfish on August 16, 2013, 03:24:28 AM
Deleted for stupidity...  :icon_rolleyes:

All fixed - apparently I have difficulty distinguishing red from brown...
Personally, I never use the colour codes on resistors, I just measure them with my MM. Then again, I have been diagnosed with colour blindness by an optometrist.
Mostly some reds and some browns are not much different.
That's another reason why I don't bother reading the colour codes. I find that the colours are never consistent, even between different batches from the same manufacturer. Another thing that bugs me is that the bands are never a consistent width, packets I get have good, thick bands, while others are almost unreadably thin.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 16, 2013, 04:30:45 PM
It's a sign of age when I've got more magnifiers than I have screwdrivers...

As I said before, fab compressor - this is the first time I've tried board mounted pots (I adapted some standard alphas) never mind a big LED so I'm pleased I got everything to line up.  :icon_cool:

Here's a couple of pics:

(http://i44.tinypic.com/2efq4pd.jpg)

(http://i40.tinypic.com/2lia2rl.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Roger Martin on August 17, 2013, 04:29:54 AM
A neat job, man.
My next project.
I read a few posts and they recommend me to pair a compressor with a big muff, is it really worth a try ?
I used the other compressor and came up with an unimpressive sound result.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 17, 2013, 05:51:26 AM
Here's a couple of pics:

Beautiful!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: gritz on August 17, 2013, 09:14:54 AM
It's a sign of age when I've got more magnifiers than I have screwdrivers...

Me too bro, me too...

Sweet build btw!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 17, 2013, 05:58:06 PM
I read a few posts and they recommend me to pair a compressor with a big muff, is it really worth a try ?
I used the other compressor and came up with an unimpressive sound result.

Most fuzz boxes have a 'compressing' effect in that they naturally squeeze the attack portion of the guitar signal. You can use the attack control on the compressor to put back some bite while adding sustain - it's a good combination (fuzz first). Add some treble back with the tone control for even more bite.

I was using the ET tonight with a fuzz face and pow! - instant Gilmour solo on 'Money' (if played by a chimpanzee...). A big muff should work well too.

By the way Merlin, if I push the input of the ET from the FF while bypassed I can get the LEDs to light up. Should this happen?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 18, 2013, 06:54:28 AM
By the way Merlin, if I push the input of the ET from the FF while bypassed I can get the LEDs to light up. Should this happen?

Assuming you have wired the ET bypass switch in the usual way (true bypass), then when bypassed there is absolutely no signal connection to the ET, so no, nothing should light up! Sounds like you have a wiring error...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Jdansti on August 18, 2013, 01:03:55 PM
>That's another reason why I don't bother reading the colour codes. I find that the colours are never consistent, even between different batches from the same manufacturer. Another thing that bugs me is that the bands are never a consistent width, packets I get have good, thick bands, while others are almost unreadably thin.

If I use color codes, I have to shine a bright light on the resistor (usually my iPhone light) and sometimes use a magnifier. Same for reading diode markings.  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 18, 2013, 04:01:24 PM
By the way Merlin, if I push the input of the ET from the FF while bypassed I can get the LEDs to light up. Should this happen?

Assuming you have wired the ET bypass switch in the usual way (true bypass), then when bypassed there is absolutely no signal connection to the ET, so no, nothing should light up! Sounds like you have a wiring error...

A wiring error wouldn't surprise me. Can you see anything wrong in the pic? I'll have another look...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 19, 2013, 06:47:44 AM
I can't see anything wrong with the wiring and it checks out with a meter. There is no physical signal connection between the input or output jacks and the circuit when bypassed. The only connection is between the circuit output and the switching FET. The switch is wired exactly as in the picture from the original ET docs.

Might it be to do with the positive ground FF?

I can also do this (FF flat out, ET bypassed):
(http://i41.tinypic.com/2n1z2go.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 19, 2013, 07:15:28 AM
I can also do this (FF flat out, ET bypassed):

Interesting... in that case I suppose it could be picking up the higher frequencies that are coupled across the switch capacitance, or possibly something is coupling into the ground. The VU is very sensitive after all. Not sure what, if anything, can be done about this. Maybe add a few picofards from the input of the ET to ground (right at the opamp input), to shunt the switch capacitance...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tpoolan on August 19, 2013, 07:21:15 AM
Thanks Merlin, I'll try that. It's not a big deal, to be honest, but I get a bit OCD about these things.  ;D

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: musiclikscreams on October 07, 2013, 10:59:11 PM
Any smaller 5 knob pcbs out there?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: waltk on October 08, 2013, 11:15:16 AM
Quote
Any smaller 5 knob pcbs out there?

You can take about 20% off the top of Merlin's latest 5-knob layout.  The only things up there are the power connector and the protection diode.  That's what I did here - and substituted a series Schottky diode for the power protection.

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49769&g2_serialNumber=2)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: waltk on October 08, 2013, 11:27:32 AM
Two questions for Merlin...

How can I reduce the brightness of the 3916 leds?

How can I adjust the low-end sensitivity of the leds (the lowest one is always on - even with no input)?

I guess it would be some adjustments to R26, R27, and/or R28.

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49772&g2_serialNumber=2)

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49775&g2_serialNumber=2)

(http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=49778&g2_serialNumber=2)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on October 08, 2013, 05:00:07 PM
How can I reduce the brightness of the 3916 leds?
Increase R26- it controls the internal current source.

Quote
How can I adjust the low-end sensitivity of the leds (the lowest one is always on - even with no input)?
Reduce R28 and/or increase R27. There are actually two resistors (R11+R28) to make it easier to adjust the total resistance to pin 6.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: waltk on October 08, 2013, 11:09:55 PM
Thanks Merlin - for the quick answer, and also for sharing this fantastic design!  I only box up about 1 out of every 20 circuits I build, and this one is a keeper.  Sounds great!
Title: A Pair of Thumbs
Post by: KazooMan on October 09, 2013, 02:52:11 PM
I liked the original version of The Engineer's Thumb so much that I had to build the 5-knob version.  I guess you could say I am "all Thumbs" now ;D

Here are the pedals.  Thanks to Merlin for the artwork concept that I unabashedly copied.  Both pedals have my homebrewed adapter to allow using a surface mounted LM13700 as I described in a previous post in this thread.  The LM13700 performs better in my opinion.

(http://i44.tinypic.com/2meqnm0.jpg)


(http://i44.tinypic.com/2qi66x0.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: musiclikscreams on October 10, 2013, 09:16:33 AM
^Amazing
Title: Re: A Pair of Thumbs
Post by: merlinb on October 10, 2013, 11:15:55 AM
I liked the original version of The Engineer's Thumb so much that I had to build the 5-knob version.  I guess you could say I am "all Thumbs" now ;D

Looks stunning! Glad you like it  ;D :D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 04, 2013, 05:28:35 PM
Hey guys,

First off, props to merlinb for this awesome design.

I've recently decided that I'd like to try to build my own pedal and thought that this project would be a great starter. I apologize for the total noob question, but I have absolutely no idea on how to wire up the input and output jacks to the vero layout (I'm using stereo jacks). I've stared and wondered at the picture of the PCB version with stereo jacks (on page 5) without having any luck. I really like how the vero layout has the wiring for the switch and the pots, and was wondering if there was a way that someone could quickly throw the input jacks and their wiring in the same way. Really all the wiring would be extremely helpful.

Here's what I have so far:

(http://i14.photobucket.com/albums/a350/plckle/IMG_20131103_181740.jpg) (http://s14.photobucket.com/user/plckle/media/IMG_20131103_181740.jpg.html)

*Note that the bottom row of the vero layout actually starts on the second from the bottom on my layout.

Also, this is my first post after being a long time lurker and drooler at some of these creations.

Any help will be greatly appreciated!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: psychedelicfish on November 04, 2013, 05:35:05 PM
This page (http://www.beavisaudio.com/techpages/StompboxWiring/) should be helpful.
If your jacks are both metal, only connect one of the sleeve tabs to the ground, and leave the other one hanging. That way you won't get a ground loop through your enclosure (ground loops act as aerials and pick up tonnes of nasty hum and radio interference). Make sure your power jack is a plastic one if you're planning to wire it center negative (what seems to be the standard for pedals).

What you have there looks pretty good for a first project!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 04, 2013, 05:44:14 PM
Oh, that link is super helpful. My jacks are plastic with 6 metal tabs. Looking at the picture on page 5 or so, I have the same jacks as those. There's a tan wire, and two black wires going straight from the jacks to the PCB. I'm not sure where they are going to.

Thanks for the reply. I've already learned a lot!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 04, 2013, 07:47:19 PM
Also, on that link you sent me, it has the wiring for a battery clip, which I will not be using any batteries for this build. So should I just wire the negative off the center and leave the other hanging, or jump them together?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on November 05, 2013, 04:06:27 AM
Oh, that link is super helpful. My jacks are plastic with 6 metal tabs.
(http://i81.photobucket.com/albums/j207/merlinblencowe/ET_jack_zps4abab50a.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 05, 2013, 07:30:26 AM
Awesome! Thanks so much. I can't wait to get this thing rolling over the weekend!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: laird on November 05, 2013, 03:26:39 PM
A few months ago I built an Engineer's Thumb but haven't been able to get it working quite right. I followed Merlin's vero board layout (on the last page of the PDF) with three modifications: Adding a release control (replace R12 w/ pot), a threshold control (replace R5 w/ pot), and a positive battery disconnect when the power jack is in use.

With the controls set at their defaults (volume and release maxed, ratio and threshold minimized) it passes audio through at unity gain with no compression. That's the closest it gets to behaving correctly. As soon as the ratio is turned above dead zero I get a significant hiss, and the output (quiet and loud alike) goes down as the knob goes up. No compression, just attenuation. Weird noises happen when the release is set to zero, but that's to be expected.

When I first built it I used a 2N3906 as the PNP transistor in Q1 and a JRC13600D as a sub for the LM13700. I might've had the 2N3906 installed backwards - it looks like its pin arrangement is opposite the BC327. A few weeks ago I put in a BC327 in Q1 and a LM13700, as well as replacing the TL074 just in case. The voltage readings are practically unchanged before vs after.

Supply: 9.34v
Q1e: 2.97
Q1b: 2.36
Q1c: 1.40

IC1 (TL074):
Op1 (constant voltage source)
1 (1OUT) 4.67
2 (1IN-) 4.67
3 (1IN+) 4.47
4 (VCC+) 9.34
Op2 (main gain stage)
5 (2IN+) 4.32
6 (2IN-) 4.67
7 (2OUT) 4.70
Op3 (side chain 1 - charger)
8 (3OUT) 4.97
9 (3IN-) 4.67
10 (3IN+) 4.67
11 (VCC-) 0
Op4 (side chain 2 - bias control for lm13700)
12 (4IN+) 2.90
13 (4IN-) 2.97
14 (4OUT) 2.36

IC2 (LM13700)
pins 1-7,10 are all 0v
pins 8 and 9 are not connected and read floating/leaking voltage that stabilizes down to around 0.3v with the multimeter connected
11 (V+) 9.34
12 (2OUT) 4.67
13 (2IN-) 4.67
14 (2IN+) 4.67
15 (2D bias) 0
16 (2A bias) 1.40

Running a square-wave signal generator into the input (2v P-P @1khz, which should be WAY more than enough to trigger compression) I don't see any change in the bias voltage going from Q1 to the LM13700. This points to something wrong with the side chain... based on the voltage readings I'd guess there's a lot of constant current flow going on there. Does anyone have any idea what I should look at next?

Thanks,
-Laird
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 11, 2013, 09:16:47 PM
Alright, I need a little bit of trouble shooting guidance. A few posts above, you can see what my layout looks like for reference.

The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

PS - 8.95

Q1
e - 4.52
b - 4.05
c - 1.09

Q2
e - 6.44
b - 0
c - 8.93

IC1
1 - 4.52
2 - 4.52
3 - 4.30
4 - 8.92
5 - 4.10
6 - 4.50
7 - 4.50
8 - 4.52
9 - 4.52
10 - 4.09
11 - 0
12 - 4.1
13 - 4.51
14 - 4.04

IC2

1 - 0
2 - 0
3 - 0
4 - 0
5 - 0.01
6 - 0.01
7 - 0.01
8 - 0
9 - 0.98
10 - 0.01
11 - 8.88
12 - 4.50
13 - 4.50
14 - 4.50
15 - 0.01
16 - 1.09

Any help would be greatly appreciated!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: waltk on November 11, 2013, 10:42:06 PM
Quote
The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

I didn't look at your voltages, and don't know anything about vero, but can explain something about measuring that 10M resistor.  If you're trying to measure it in-circuit, and getting zero resistance, that just means your input is shorted to ground.  That resistor goes directly from input to ground, and is unlikely to be bad (as you found when you measured it out of circuit).  When you measure something in-circuit, you're really measuring it and everything it's connected to.  So it could be that your input is being shorted to ground somewhere off-board (like in your switch or jacks), or it could be a solder bridge or misconnection elsewhere on the board.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 11, 2013, 10:48:59 PM
Quote
So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1.

Was the pedal powered when you measured resistance? It has to be on to measure voltages but it has to be off to measure resistance.

What layout or schematic are you referring to?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 12, 2013, 07:40:04 AM
Quote
The issue is that when the pedal is engaged, I get no audio. When bypassed, my signal runs through just fine, as it should. So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1. Thinking that it may have been a bad resistor, I replaced it, checked the new one, same thing - 0 value. I checked the old one and it right around 10M as it should. The majority of the other resistors I've checked have been reading correctly as well.

I didn't look at your voltages, and don't know anything about vero, but can explain something about measuring that 10M resistor.  If you're trying to measure it in-circuit, and getting zero resistance, that just means your input is shorted to ground.  That resistor goes directly from input to ground, and is unlikely to be bad (as you found when you measured it out of circuit).  When you measure something in-circuit, you're really measuring it and everything it's connected to.  So it could be that your input is being shorted to ground somewhere off-board (like in your switch or jacks), or it could be a solder bridge or misconnection elsewhere on the board.

Ah, I see. I'm using the layout that merlib gave - it's a few posts above, and also on the first page which also has the schematic. It goes straight from input to the ground, as you can see in the layout, which explains the 0 value. A solder bridge is what I'm afraid of, but there doesn't seem to be anything that I can see.

I apologize, this is my first build so I'm still trying to learn how these things work.

Quote
So far, the strangest phenomenon that I've had is when using a multimeter, there is a 0 value when testing the resistance on R1.

Was the pedal powered when you measured resistance? It has to be on to measure voltages but it has to be off to measure resistance.

What layout or schematic are you referring to?

The pedal was powered on when I measure the voltages I listed, but was unpowered when I measured the resistance. So, I at least did that right.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on November 12, 2013, 07:49:53 AM
just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's :icon_evil:...man those snide chips can really waste a LOT of time and effort.. :(

i have new IC's now.. buy cheap, pay twice i guess. ::)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 12, 2013, 11:45:38 AM
just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's :icon_evil:...man those snide chips can really waste a LOT of time and effort.. :(

i have new IC's now.. buy cheap, pay twice i guess. ::)

At this point, I'm hoping that it's a solder bridge rather than that. Fortunately, I believe I have 4 other 13700's lying around, so hopefully I have at least one good one if that is the case.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 12, 2013, 12:46:24 PM
just a note on why my attempts to breadboard this, and the mutron v, and ms20,  failed :  fake bloody 13700's :icon_evil:
i have new IC's now.. buy cheap, pay twice i guess. ::)

Booya! Happy to see D'Astro back in the OTA game. Quite a chip...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on November 12, 2013, 12:54:22 PM
@inlimbo:  yep hopefully.

i had 4 that were ....... .......

@gary: yep just finishing up some stuff, then i'll be back on these projects..  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on November 12, 2013, 02:21:55 PM
At this point, I'm hoping that it's a solder bridge rather than that.

Your voltages look OK, and I can't see any problems with the top side of the board. Did you add a status LED and does it work?

Most common things to look for:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 12, 2013, 02:35:46 PM
At this point, I'm hoping that it's a solder bridge rather than that.

Your voltages look OK, and I can't see any problems with the top side of the board. Did you add a status LED and does it work?

Most common things to look for:
  • A trace that is supposed to be cut but hasn't.
  • A trace that has been cut in the wrong place.
  • Incorrectly wired off-board components.

Thanks for the reply, Merlin. I tried both with and without an LED. I'm using the same LED for this as the protection LEDs for testing, and it does light up when the pedal is engaged.

So far, the thought about the input going straight to ground seems to be the most plausible. When I get a chance over the next day or so, I'm going to try and get a shot of the underneath side of the board along with the off-board components I have soldered for testing purposes.

Thanks for your help so far - I'm glad I've chosen this as a first try as you've been extremely helpful.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 13, 2013, 11:34:31 AM
Here's the pics of the bottom side of the board and the off-board wiring. Please note that the janky Radio Shack battery clip cable broke while positioning it for the picture. This battery clip is for testing purposes only - my final build will not have any battery capacity, as I have a powered pedal board. On the underside of the board, I left R1 leads uncut to easier test the resistance with a meter.

Any feedback will again be appreciated!

(http://i14.photobucket.com/albums/a350/plckle/IMG_20131113_112741.jpg) (http://s14.photobucket.com/user/plckle/media/IMG_20131113_112741.jpg.html)

(http://i14.photobucket.com/albums/a350/plckle/IMG_20131113_112603.jpg) (http://s14.photobucket.com/user/plckle/media/IMG_20131113_112603.jpg.html)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 13, 2013, 12:39:06 PM
^ did you do a continuity check with your DMM?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 13, 2013, 01:25:13 PM
With work and school and all, I haven't been able to touch it, but will definitely have a chance tonight. The idea of the input being sent straight to ground hadn't occured to me until the following morning, and I haven't had a chance to do any continuity tests on the input between the switch and on board. I know the switch has continuity where it should as I've tested that already, but that's about as far as I've tested the input.

I initially thought it was something to do with the components, hence the reason I posted the voltages. Since I've found that the voltages check out, that points even more to the input signal getting lost. I'm really hoping that I'll have it working tonight.

Again, thanks for the assistance. You guys are great, and I'm happy to have joined the forum.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: InLimbo on November 13, 2013, 08:11:26 PM
CRISIS AVERTED, GUYS.

The absolute smallest solder bridge between the input row and ground. Works perfectly now.

Thanks for all of your help! Now to get the enclosure ready!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on November 14, 2013, 02:55:56 PM
i'm building another one of these to give to some undetermined person (ie. i'm bored and they're fun to make). probably a dumb question, but i ordered a bunch of these LEDs hoping for the most "standard" rating of red LEDs, and i was wondering if anyone could let me know if they'd be suitable for achieving the 3.2Vp-p input limit to prevent clipping: http://www.rapidonline.com/electronic-components/kingbright-l-7113id-5mm-2v-red-diffused-led-45mcd-55-0155 (http://www.rapidonline.com/electronic-components/kingbright-l-7113id-5mm-2v-red-diffused-led-45mcd-55-0155). i think i gather that the forward voltage is 2V, reverse is 5V (?), but in all honesty i don't see the number 3.2 anywhere so thought i'd ask! lol
i omitted them from my own build as i knew it'd always be first in my chain and the signal would be nowhere near the headroom limit.

cheers
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: psychedelicfish on November 14, 2013, 04:24:59 PM
If you look at the datasheet for those LEDs, you'll see a graph titled forward voltage vs. forward current. You'll notice that there is a smooth curve starting at about 1.7V. When the input signal reaches 1.7V the LEDs will begin to conduct, and as the voltage increases, the LEDs will conduct more. This results in a soft clipped waveform, and the 3.2V is just an estimation for the peak to peak voltage of this clipped waveform. The reason for these LEDs is that if you feed a large signal into the ET, the LEDs will clip it softly, rather than the OTAs hard clipping it, which means it wont sound absolutely disgusting if you momentarily overdrive it.

So, in short, yes those LEDs should be fine.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on November 15, 2013, 09:44:07 AM
thanks for the explanation, Edward - i think i get now that it's not such a sudden cut-off from the forward voltage, as it were. there were red LEDs with different voltages marked in the title, which made me paranoid in case i'd bought some special niche one lol. either i overthink or i think in the wrong areas.

all i'm lacking are a bunch of 10k resistors, and since i slept through the post this morning, 100 of them will be stuck in a warehouse until monday, when i'm busy with band stuff. this is most uncool. hmm, there are only three 10k's in the circuit, maybe it wouldn't look too atrocious to stick together some 4.7ks or something. closest values in the region i have are 8.2 and 15k.

damn, just realised a few caps i don't have were in that order, too. worst day ever! lol
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on November 15, 2013, 11:19:21 AM
^ just go to Radio Sha...  oh, yeah, never mind  :P
Title: Re:
Post by: jtn191 on November 16, 2013, 06:27:40 PM
I built mine up and I get a volume boost and more compression as the ratio pot is turned...is that normal?
Title: Re:
Post by: midwayfair on November 16, 2013, 08:33:25 PM
I built mine up and I get a volume boost and more compression as the ratio pot is turned...is that normal?

Yes ... More resistance in the feedback loop.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on November 19, 2013, 10:34:56 AM
Edit: ignore this entire post - upon fixing an error within the ET circuit itself (that i should've noticed) and trying a different batch of 2n7000s, it works. well, at least i managed to track it down by thinking out loud lol. cheers anyway!

my latest build of this seems to work great - but i'm having flashbacks to the weird Millennium Bypass issues i had with the original! around the time i seemed to have bad luck with MOSFETs generally so i phobically switched to the JFET Millennium 1 for a while. haven't tried that with this yet. i'm posting this here because i can't help but think my problem is at least partly to do with resistance to ground on this particular circuit. everyone else's seems fine, so i want to work out what i'm missing.

i get the Millennium working independently, ie. grounding the control line switches it off, but when wired to the DPDT switch, it would only go off if the volume pot was turned CCW slightly. Then, after clicking the DPDT once or twice, it seems the MOSFET dies and it needs replaced. maybe using a NPN as a low-leakage diode would help with the sudden death?

i've tried a coupla 1n4148s to rule out leakage issues. 2 in parallel doesn't seem to help. adding a 2.2M resistor to ground after the volume pot (which might screw up the taper, no?) doesn't work.

sorry for yet another redundant issue on this topic, in my defence i'm just a fan of the Engineer's Thumb! lol. "I built a kick-ass compressor in a day... but i can't get the light to come on" doesn't have such a great ring to it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MrStab on November 19, 2013, 11:10:29 PM
observation: i've built two of these now, and both have shown issues with ticking/LED flashing when bypassed, unless you ground the input. easily done by shunting the signal via. a NPN, but worth noting.

The extra controls are not terribly useful ... there will be some "broken" settings on the attack and decay controls

( http://www.diystompboxes.com/smfforum/index.php?topic=101630.msg898103#msg898103 (http://www.diystompboxes.com/smfforum/index.php?topic=101630.msg898103#msg898103) )

i've also noticed the above, and the ticking is affected by the Release pot. i wonder if a combination of using all 5 controls (or just deviating from stock values) and everyone else using 3PDTs which ground the input anyway is why no-one else has noticed the ticking.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jtn191 on December 14, 2013, 07:57:44 PM

i've also noticed the above, and the ticking is affected by the Release pot. i wonder if a combination of using all 5 controls (or just deviating from stock values) and everyone else using 3PDTs which ground the input anyway is why no-one else has noticed the ticking.

In my build, I don't currently have any problems with ticking or "broken settings" on the controls. I forwent the millenium bypass circuit and used a 3pdt, grounding input on bypass. I did end up reverse wiring the attack and threshold controls because they operated backwards from how I wanted/expected them to...counter-clockwise should be a short attack time, meaning reduced attack volume and a low threshold should mean more compression for a given ratio...could be my mistake drafting the pcb layout

However, I'm having problems on my second build. This one is a two knob control scheme and I'm experiencing much lower volume output. I'm thinking it may be that I included the 220k resistor near the 1M release resistor...the 220k isn't present on the two knob schem. My 4.5v test points are sitting at 4.8v
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on December 15, 2013, 05:26:27 AM
I'm thinking it may be that I included the 220k resistor near the 1M release resistor...the 220k isn't present on the two knob schem.
That's unlikely to be the problem. You want the total release resistance to be somewhere between 220k and 1.5M. That's why it is there in the 5 knob version- it stops the release resistance from being turned all the way to zero ohms.

Quote
My 4.5v test points are sitting at 4.8v
Suspicious...

Title: Re:
Post by: jtn191 on December 24, 2013, 05:10:47 PM
Found the problem! My 220r resistor was ~2.79k
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jtn191 on January 01, 2014, 08:11:53 PM
Really enjoying your preamp book, Merlin! I got it for Christmas. Reading the explanations and alternate solutions is seriously addicting

I was just checking to see if I had my release control wired properly when I decided to do a little analysis of the range of attack times on the E.T. I found it to be ~4ms-160+ milliseconds. Higher attack times are tricky to measure, so I wouldn't be surprised if it's larger!

(http://i.imgur.com/UfK5K3V.png) (http://imgur.com/UfK5K3V)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kbibs on January 02, 2014, 12:36:44 PM
Hi Everyone and Happy New Year!

I built the two knob version of this on a prototype board and it sounds really nice. I like it alot, thanks Merlin! ... Before building it into a pedal (actually the 5knob GT1 version I plan on building) I wanted to play around with decreasing the release time. So I lowered the 1M release time resistor down to 220k and now I hear a ticking noise, almost like static, after the initial attack say during the release and for some time after. It definitely reduced the release time but now with this noise. I then increased it to 511k and the amount of ticking decreased but its still there. With 1M I don't hear it. Like I said I only hear it after the initial attack and usually after play a chord (stronger signal maybe?) rather than single notes. I built it with the led protection diodes and without the Millenium Bypass. Other than this the compressor is functioning as expected. This sounds similar to what some of you have experienced so I was wondering if anyone has found what is causing this? or what they changed to eliminate it? ... I plan on triple checking my component values and maybe trying some different diodes but other than that I'm not sure what to try.

Thanks,
Ken
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kbibs on January 04, 2014, 05:04:57 PM
Found it!!! ... the second 1uf cap after the rectifier was not grounded. It's very quiet now!

Thanks,
Ken
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: NCSUZoSo on January 11, 2014, 09:49:52 PM
Out of curiosity, what is the build cost for this pedal (not including enclosure, but everything else)?

Also I have seen a 5 knob version of this, how much does that affect cost?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: waltk on January 12, 2014, 11:01:20 AM
Quote
Out of curiosity, what is the build cost for this pedal (not including enclosure, but everything else)?

Like all DIY pedals, it costs every bit of your spare time, many dollars to buy all the tools and supplies you need (and some you don't need), and possibly your sanity...

Real answer: depends on what you already have, and how you build it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 12, 2014, 11:35:21 AM
Out of curiosity, what is the build cost for this pedal (not including enclosure, but everything else)?
Looking at the BOM for the basic version:
17 resistors, $0.17
8 capacitors, $0.8
3 ICs, $2
2 transistors, $0.2
8 Diodes, $0.08
Sockets and footswitch, $10
Total: $13.25

Call it $20 since I'm working in dollars, which are foreign to me!  :icon_lol:

I would guess the 5-knob version would add about $15 on top of that, at most.

Title: Re:
Post by: jtn191 on January 12, 2014, 02:22:08 PM
The only difference is 3 more pots, 3 more knobs, what seems like much more wiring
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on February 18, 2014, 07:37:48 AM
Hopefully this is not too far off topic. I have a hypothetical question about the precision current source in the ET.

Say I wanted to drive 2 OTAs (i.e. both sides of an LM13700) with the ET's envelope detector. Can I:
- halve the 1k resistor to Vref and then split signal from the BJT's collector with a couple of low value resistors.
- parallel two BJTs, each with their own 1k and 1M resistors?

Are these reasonable, and/or is there a better way?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on February 18, 2014, 08:03:49 AM
Say I wanted to drive 2 OTAs (i.e. both sides of an LM13700) with the ET's envelope detector. Can I:
- halve the 1k resistor to Vref and then split signal from the BJT's collector with a couple of low value resistors.
- parallel two BJTs, each with their own 1k and 1M resistors?

The first way is a bit dodgy because current probably won't divide equally between the two OTAs, and you don't want to overdrive one or the other. It might work with decent sized collector resistors, but unfortunately there isn't enough voltage headroom available for large resistors.

The second method has the same problem with current sharing, but this time between the two transistors.

A better way is to connect only the base of the second transistor to the base of the first one, but no other parallel connections. Both transistors have their own 1k/1M. Use matched transistors.

What is it you're trying to do? Why do you want to control two OTAs with the same control voltage?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on February 18, 2014, 08:22:46 AM
OK, that makes sense. I didn't like option 1, and I guess option 2 should keep the op-amp happier - Thanks Merlin.
Something like this (sorry about the resolution)?
(https://dl.dropboxusercontent.com/u/11996927/1-PCS-2-OTA.jpg)

What do I want it for? Mostly a thought experiment at this stage - a few ideas:
A stereo ET, if the signals were summed before going into the envelope detector
A compressor with a noise gate on the front end and a common envelope detector...


Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on February 18, 2014, 08:28:22 AM
Something like this (sorry about the resolution)?

Yes that's what I meant. It might be nice to add a protection diode on the other transisitor too, from base to emitter, although I may be being over cautious...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on February 18, 2014, 09:06:34 AM
Yeah, I noticed some interesting spikes in the simulations. Diode added, and will let you know if I ever get to the breadboard stage.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jtn191 on April 20, 2014, 05:01:56 AM
In studying the attack/release times of more compressor pedals, I thought I'd suggest lower value pots for attack/release...possibly log taper for attack. With 1M, the ET gives 4ms-160ms attack time but most of the usable-for-electric-guitar values are scrunched up in the low values. Dynacomps have 5ms, my Orange Squeezer is sitting at ~22ms (which is what I'd consider near the longer end of what a guitar player would want), Demeter Optocomp is spec'd at 1ms. I may try 1MA, 500KB/A, or 100K/A
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on May 01, 2014, 12:57:14 PM
Playing with bits of this on the breadboard - it is a very nice circuit. What is the 1k in the feedback path of U1A doing and/or why is it not directly at the output of the OTA?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 01, 2014, 04:05:41 PM
Playing with bits of this on the breadboard - it is a very nice circuit. What is the 1k in the feedback path of U1A doing and/or why is it not directly at the output of the OTA?
TBH, I doubt it is needed for anything. But something about connecting the output of the OTA directly to the input of the opamp gave me the willies, so I put in the resistor for a bit of 'compliance' as it were. But if it works the same for you, feel free to leave it out.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on May 01, 2014, 04:18:17 PM
^something about connecting the output of the OTA directly to the input of the opamp gave me the willies
You and me both. It works fine without it, but I will be leaving it there.

The thing that threw me was that you placed it in between the (-) input and the resistor to (virtual) ground. I'm guessing there is no magic in placing it there rather than straight off the output of the OTA?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 01, 2014, 04:27:16 PM
I almost posted a thought about the 1K working against the 100pFd to force a tame phase-curve around two cascaded gain-chips in a loop.

However the OTA output is 9,999 or 4,999 Ohms, so another K didn't seem to make much difference.

Then I realized that, for DIY one-off, it is NOT worth fretting over a 12 cent resistor.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on May 01, 2014, 04:37:49 PM
^Then I realized that, for DIY one-off, it is NOT worth fretting over a 12 cent resistor.
Not fretting, just trying to work out how it works and whether something unexpected will happen if I poke it with a stick...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tombaker on May 28, 2014, 07:56:22 AM
Just built this vero version up and replaced it in my fuzz face DI. The fuzz face wasn't that useful but I've just run drums, bass, guitar and vocals through this and it's really useful.
I've currently only got ratio and volume hooked up but I might add a release knob just for some versatility with shaping.
I like using guitar pedals during a mix and have been using the boss blue comp with monte allums mod which is great and this is just a whole new colour.
So thanks Merlin, much appreciated.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: seedlings on June 06, 2014, 06:27:42 PM
Time to build a compressor.

There was one post in this thread that said the LM13600 works in place of the LM13700.  Would there be any considerations in the substitution - anything to change from the page one 2 knob layout?

Mucho Gratis!

CHAD
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jtn191 on June 10, 2014, 11:35:33 PM
http://www.ovnilab.com/reviews/thumb.shtml A review by a bass player/compressor fan
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on June 10, 2014, 11:45:29 PM
Quote
There was one post in this thread that said the LM13600 works in place of the LM13700.  Would there be any considerations in the substitution - anything to change from the page one 2 knob layout?

No difference, use either.

LM13600 vs LM13700 Revisited (http://www.diystompboxes.com/smfforum/index.php?topic=32660.0)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: seedlings on June 11, 2014, 08:53:28 AM
Quote
There was one post in this thread that said the LM13600 works in place of the LM13700.  Would there be any considerations in the substitution - anything to change from the page one 2 knob layout?

No difference, use either.

LM13600 vs LM13700 Revisited (http://www.diystompboxes.com/smfforum/index.php?topic=32660.0)

Thank you!  The off-board pots are all I have left before first testing.

CHAD
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: seedlings on June 12, 2014, 12:58:34 AM
AAAAAaaaaaaand... will a germanium PNP work OK?  It's a GT108V.  I ask because there is clean signal, louder with ratio rotation, but no compression.

CHAD
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: orangepit on August 31, 2014, 05:57:10 AM
For anyone who wants to use the pcb by batelfixx from page 4...
It's too low resolution in the pdf and pads close to each other seem to haze together, so I photoshopped the components out of the high res layout image. It etches beautifully.
It is 300dpi and the dimensions are written.
(https://dl.dropbox.com/s/efl58ihduu0tesj/Engineer%27s%20Thumb%20PCB%20Done.png?dl=0)

I don't have the two film 1uF caps so it isn't completely populated yet. I'll probably stick my only 1uF in one slot and a nonpolar alum cap in the other for the time being. the bare space on the top left is where the millennium [won't] go.
(https://dl.dropbox.com/s/nre02yltauy417w/Eng%20Thumb%20pop%20PCB.jpg?dl=0)

Don't use this PCB! It's wrong. I should have checked it carefully considering it was the guy's first pcb. Nothing but heavy distortion. The part after the two diodes leading to the two 1uF caps is screwed up. I haven't checked anything else.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tombaker on September 16, 2014, 06:15:03 AM
Will a charge pump do any good?
A max1044 voltage doubler specifically.
I searched the thread and can only find a mention of it from midwayfair early on but no follow up.
The IC and transistor datasheets will allow it but what other considerations should I be taking into account?
Thanks

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on September 16, 2014, 08:14:56 AM
Will a charge pump do any good?
A max1044 voltage doubler specifically.
I searched the thread and can only find a mention of it from midwayfair early on but no follow up.
The IC and transistor datasheets will allow it but what other considerations should I be taking into account?
Thanks

http://www.diystompboxes.com/smfforum/index.php?topic=97123.msg912480#msg912480
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tombaker on September 16, 2014, 09:03:38 AM
thanks sam
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on September 16, 2014, 10:43:36 AM
Higher / bipolar rail voltages are not directly applicable to this circuit. It is optimised for 9V. With more voltage the circuit needs modifying to ensure the OTA can't be burnt out by excessive control current. The end result is that this doesn't really buy you any extra headroom, because you have to turn the gain up proportionally to get the same level of comrpession as with the stock 9V circuit. This might be suitable for studio applications, but not direct guitar use.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tombaker on September 17, 2014, 03:52:14 AM
Higher / bipolar rail voltages are not directly applicable to this circuit. It is optimised for 9V. With more voltage the circuit needs modifying to ensure the OTA can't be burnt out by excessive control current. The end result is that this doesn't really buy you any extra headroom, because you have to turn the gain up proportionally to get the same level of comrpession as with the stock 9V circuit. This might be suitable for studio applications, but not direct guitar use.

Hey Merlin,
Thanks for addressing that. I have the ET installed in a small DI box in front of a transformer and I use it between my soft synths and the FOH desk at live gigs.
It helps to keep the different synth/piano/organ patches closer in loudness and the transformer smooths out some of the nasty high frequencies from the computer.
But I still run it off a 9V onespot along with my guitar pedals.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cozybuilder on September 28, 2014, 01:32:45 PM
Finally got around to finishing mine- thanks Merlin for a superb circuit design. This build uses 16mm Alpha pots, ¼ watt resistors (except the LED 22K), follows the original schematic.

(http://i1362.photobucket.com/albums/r688/russrutledge/DSCN2151_zps5fc319a8.jpg)

(http://i1362.photobucket.com/albums/r688/russrutledge/DSCN2153_zpsb63f791e.jpg)

Obligatory gut shot

(http://i1362.photobucket.com/albums/r688/russrutledge/DSCN2156_zpsf901718a.jpg)

What's under the card

(http://i1362.photobucket.com/albums/r688/russrutledge/DSCN2145_zps9e664b95.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mth5044 on September 29, 2014, 09:57:00 AM
Nicely done! You are indeed a cozy builder. That's tight.

Merlin - I'm not familiar with studio type compressors and whatnot - what does a gain reduction meter indicate? A real time level of compression?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: duck_arse on September 29, 2014, 11:42:47 AM
I see letraset, just as I remember it ^. nice work, cozy, I like the thumb-print.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: orangepit on September 30, 2014, 07:52:42 AM
Wow, your pedal looks remarkably similar to mine:

(https://dl.dropbox.com/s/mouw3juw2heg877/EngThumb.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cozybuilder on September 30, 2014, 08:10:25 AM
@orangepit-
Real nice!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: orangepit on October 01, 2014, 06:50:01 AM
Thanks. It's funny how we both envisioned our future pedals as yellow with a black thumbprint on it  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on October 04, 2014, 06:29:22 AM
I'm not familiar with studio type compressors and whatnot - what does a gain reduction meter indicate? A real time level of compression?
Yes, it shows by how much the signal has been squashed compared with what it would have been without the compressor working. It allows you to see when the compressor is actually doing something!

Cozybuilder- it's sooo tiny!  ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bloxstompboxes on January 02, 2015, 08:54:32 PM
Gotta ask a dumb question here. I see there is a 10M resistor at the input going to gnd. It's in the usual pull-down position. Any reason why so high a value? i have none of these and neither does smallbear. I haven't wired this up yet as i need to order the NJM13600D. Seems a 1 meg would be fine. I went ahead and put in the largest I have, a 4.7M. Just wondering.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on January 03, 2015, 09:39:32 AM
A 4M7 will work just fine as an input pulldown resistor.
I suspect that Merlin specs a 10M as it is an order of magnitude bigger than the input bias resistor. It can thus be largely ignored in determining the input impedance, which is ~ 1M - a fairly common modern standard.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bloxstompboxes on January 03, 2015, 09:54:10 AM
Kk, thanks Sam!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: wacko on May 09, 2015, 03:20:02 PM
Here you go, a single-sided version:
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf

Are these still available? Dropbox says the file is not found :(
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 10, 2015, 11:25:12 AM
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf
Are these still available? Dropbox says the file is not found :(
I have fixed the PDF link, but I can't seem to find the bitmap at the moment...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bloxstompboxes on May 10, 2015, 11:35:49 AM
I have my own layout available if necessary. Might be larger and not as tidy, but it works.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: wacko on May 10, 2015, 01:06:06 PM
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf
Are these still available? Dropbox says the file is not found :(
I have fixed the PDF link, but I can't seem to find the bitmap at the moment...

That is great, thank you!!!

Was the bitmap the same black&white mask that's in the pdf?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 10, 2015, 01:37:15 PM
Was the bitmap the same black&white mask that's in the pdf?
Yes the very same.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: wacko on May 14, 2015, 05:06:25 AM
Was the bitmap the same black&white mask that's in the pdf?
Yes the very same.

Thanks :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: iampoor on May 27, 2015, 06:12:25 AM
So Ive read through the whole thread....and Im still having some issues.With any compression, Im getting some noticable distortion. It sounds like parasitic oscillation/instability. On lower ratio settings, it starts distorting that sort of "fizzes" out. I have built the circuit a few times, and am using genuine LM13700's (Got them from TI).

VOltages seem fine, Ive done multiple builds and the schematic/builds seem to match. Any idea where to start from here?
Im writing this at 3am.....very discouraged, so sorry if Ive missed something obvious!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: iampoor on May 27, 2015, 09:38:59 PM
https://youtu.be/OEzybiIzO-4

Little video showing the issue
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cozybuilder on May 27, 2015, 10:22:25 PM
Are you getting any signal on the collector of the transistor? It kind of looks like you are getting just amplified signal out of U1a feeding the output. Might as well check and see if the 1K from the transconductance out is really 1K, not infinite.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: iampoor on May 28, 2015, 12:17:11 AM
Are you getting any signal on the collector of the transistor? It kind of looks like you are getting just amplified signal out of U1a feeding the output. Might as well check and see if the 1K from the transconductance out is really 1K, not infinite.

Actually, I am only getting around 1v DC on the collector, and I cannot see any AC signals on my oscillioscope....hmmm

Looking at the signal, I dont see much of anything except some small ac bursts, that start at the output of u1b. WHat should I be seeing on the collector?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 28, 2015, 01:39:23 AM
> 1v DC on the collector, and I cannot see any AC

This is correct; and this is NOT a good point to be poking at. It should always sit very near 0.6V (or 1.2V?), and is VERY sensitive to static discharge.

The OUTput of the OTA (goes to the 1K which Russ mentioned, into the signal opamp) should show signal for large inputs. Also look at the emitter of the transistor-- this sits high at idle and drops negative for large signals.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cozybuilder on May 28, 2015, 08:57:16 AM
I think the problem is related to the TCA- either its not getting input, or output, or the 1K is open, or the TCA is defective. You've checked voltages, and component values. From your video, it looks like the first op-amp is simply amplifying and clipping the signal as you increase the feedback (the 1M pot). So I would concentrate initially on verifying signal into the TCA, and the bits surrounding the TCA (wiring, solder joints etc.) It could simply be a bad chip too.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: sajy_ho on June 28, 2015, 03:08:30 AM
Hi guys, I built the circuit using Merlin's PCB and having exactly the same issue as once mentioned here:
https://youtu.be/OEzybiIzO-4

Little video showing the issue
Following your above posts I checked all the connections around the input and output of the OTA and everything seems to be OK.
Also I replaced the chip with another LM13700, and even subsituted it with a CA3080 and still having the same problem. Here is my voltage readings:

Q1:
Pin 1:  1.03
..... 2:   4.86
..... 3:   4.5
 
U1:
Pin 1:   4.5
..... 2:   4.5
..... 3:   2.21
..... 4:   0
..... 5:   2.21
..... 6:   4.06
..... 7:   4.5
..... 8:   9.02

U2:
Pin 1:   4.86
..... 2:   4.5
..... 3:   4.5
..... 4:   0
..... 5:   3.00
..... 6:   4.5
..... 7:   4.5
..... 8:   9.02

U3:
Pin 1:  1.03
..... 2:   0
..... 3:   4.5
..... 4:   4.5
..... 5:   4.5
pins 6-10:   0
pin 11:  9.02
Pins 12-16:  0

So what could cause the OTA not work?
Any help would be appreciated...

Thanks
Sajad
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Groovenut on July 08, 2015, 02:26:47 AM
Just wanted to say thanks to Merlin for the great circuit! I had to do a few tweaks to get it to my spec but that's because I love subtlety and as speced was far from subtle ( I realize that's part of the point, a Dynacomp is far from subtle too). I do love that this has the ability to be as subtle as my optical comps and yet can get rude about it too.  :icon_biggrin:

(http://lawrencepetrossdesign.weebly.com/uploads/3/1/4/1/31412717/8404239.jpeg)
(http://lawrencepetrossdesign.weebly.com/uploads/3/1/4/1/31412717/21408.jpeg)
(http://lawrencepetrossdesign.weebly.com/uploads/3/1/4/1/31412717/4177028.jpeg)
(http://lawrencepetrossdesign.weebly.com/uploads/3/1/4/1/31412717/8603472.jpeg)


Note: these pics were taken before my subtlety mods and are of Merlin's original posted values
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Groovenut on July 08, 2015, 05:49:30 PM
Quick question for Merlin,
Is there any way to get a slight overall volume increase? It would be nice to have a bit more room to go at the end of the level pot

Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 09, 2015, 06:23:26 AM
I had to do a few tweaks to get it to my spec but that's because I love subtlety and as speced was far from subtle....

Care to share what your tweaks are?

Oh, and a very nice build!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 09, 2015, 08:24:01 AM
Quick question for Merlin,
Is there any way to get a slight overall volume increase? It would be nice to have a bit more room to go at the end of the level pot

Thanks!

I'm not Merlin but I've read that increasing the voltage (some have experimented with charge pumps) provides a noticeable gain in headroom.
I have a couple questions myself if anyone cares to answer.

Is a LM13700 suggested because of it's price and availability "~$1.10+"? There's a strip board layout (http://tagboardeffects.blogspot.com/2012/11/engineers-thumb.html) using a CA3080(an 8 pin IC used in a Dynacomp I've read?) "~$5+" I've read all over the place that the LM13700 is two of the CA3080s. With some obvious tweaks I'm not in tune with it yet. I'll draw out it's schematic to compare later.

First off I've noticed IvIark -the guy who shared it has omitted the 1n4001 as well as the BS170 MOSFET. Are those in Merlin's schematic for some kind of "old-school" bypassing, for use of an VU meter on the LED of the MOSFET or some other reason?

Random question out of curiosity, I believe there are TO-99 (metal can type package) of CA3080 "ua308HC (http://www.ti.com/lit/ds/symlink/lm308-n.pdf)" as well as TO-99 dual opamp ICs such as "LM358H (http://www.mouser.com/ds/2/405/lm358-n-443917.pdf)". Still trying to find a decent match for a TL07x type IC. Although not ideal due to the price - is it possible/practical to use the metal can type of ICs instead?

I'm still a young learner trying to wrap my head around it all. Thanks for everything guys.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on July 09, 2015, 10:16:20 AM
First off I've noticed IvIark -the guy who shared it has omitted the 1n4001 as well as the BS170 MOSFET. Are those in Merlin's schematic for some kind of "old-school" bypassing, for use of an VU meter on the LED of the MOSFET or some other reason?

It's a Millenium bypass variant so that you can switch the both the LED and the effect on and off using only a DPDT.  (Check out GEOFEX for more on this - link at top of this page.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 10:26:24 AM
There is a metal can CA3080-- I will advise to steer away.  I have gotten them in the past from China to keep the cost down, but the quality has nose-dived in the last year, and I CAN NOT find a satisfactory source anymore.  (Other than expensive NOS supply).

The plastic DIP style CA3080A is cheaper/easier and readily available, however.

MC
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 09, 2015, 11:06:37 AM
It's a Millenium bypass variant

That's what I assumed but thought it was odd seeing this in a schematic dated in 2012. I refreshed my knowledge on everything regarding the millennium bypass last night. Using it is redundant these days due to the low cost of 3pdt switches. Not sure if the 2n9001 is part of the bypass as well so I'm hoping someone could explain.

Also is there any differences on the effectiveness of the circuit between using a LM13700 or a CA3080? I'll snag both to breadboard next week.

There is a metal can CA3080-- I will advise to steer away.  I have gotten them in the past from China to keep the cost down, but the quality has nose-dived in the last year, and I CAN NOT find a satisfactory source anymore.  (Other than expensive NOS supply).

The plastic DIP style CA3080A is cheaper/easier and readily available, however.

MC

Thanks for the info! I've noticed smallbear had a ua308HC and thought it would be cool to use the TO-99 type ICs which seems uncomon. I'll steer away and try to keep this hobby budget friendly  :icon_wink:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Groovenut on July 09, 2015, 11:23:43 AM

I had to do a few tweaks to get it to my spec but that's because I love subtlety and as speced was far from subtle....

Care to share what your tweaks are?

Oh, and a very nice build!
thanks Sam!

Realistically all my current tweaks can be easily done on the 5 knob version but since 5 knobs won't fit here's the list.

Reduced release time, 470k
Increased attack time, changed 100R to 47R and a series 100k trimmer
Changed the Ratio pot value to A500k since I found the most aggressive compression I use was just past noon on the original value.
Slightly raised the threshold to accommodate higher output pickups with more subtlety.

I'm still thinking there may be a way to gain a little more output without upsetting the balance of the circuit though. Still experimenting.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Groovenut on July 09, 2015, 11:30:15 AM

Quick question for Merlin,
Is there any way to get a slight overall volume increase? It would be nice to have a bit more room to go at the end of the level pot

Thanks!

I'm not Merlin but I've read that increasing the voltage (some have experimented with charge pumps) provides a noticeable gain in headroom.
I have a couple questions myself if anyone cares to answer.
Merlin has said the circuit is optimized for 9 volts and increasing the supply won't actually help much. I'm definitely not having headroom or distortion issues. It's a very clean circuit. I would just like to afford some more room between unity gain and the end of travel on the level pot :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 09, 2015, 11:41:52 AM
Reduced release time, 470k
Increased attack time, changed 100R to 47R and a series 100k trimmer
Changed the Ratio pot value to A500k since I found the most aggressive compression I use was just past noon on the original value.
Slightly raised the threshold to accommodate higher output pickups with more subtlety.

I'm still thinking there may be a way to gain a little more output without upsetting the balance of the circuit though. Still experimenting.

Thanks.

If you want more output without further increasing the threshold - I take it you used a 1M trimmer like the 5 knob version? - then you could try increasing (don't decrease!) the value of either:

1. the 10k resistor feeding the LM13700's (+) input.
2. the 1k resistor between Vref and the PNP's emitter.
Title: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Groovenut on July 09, 2015, 11:54:26 AM
Reduced release time, 470k
Increased attack time, changed 100R to 47R and a series 100k trimmer
Changed the Ratio pot value to A500k since I found the most aggressive compression I use was just past noon on the original value.
Slightly raised the threshold to accommodate higher output pickups with more subtlety.

I'm still thinking there may be a way to gain a little more output without upsetting the balance of the circuit though. Still experimenting.

Thanks.

If you want more output without further increasing the threshold - I take it you used a 1M trimmer like the 5 knob version? - then you could try increasing (don't decrease!) the value of either:

1. the 10k resistor feeding the LM13700's (+) input.
2. the 1k resistor between Vref and the PNP's emitter.
thanks Sam. That was my thought but wanted confirmation. I'm thinking since I'm into more subtle compression the increase in threshold should  get me where I want. Question though, increasing the 1k on the emitter would reduce current to the OTA therefore decreasing the output of the OTA via control current whereas increasing the 10k at the + input of the OTA would reduce the output via less input, both resulting in more overall output level, however will the method used change the outcome or is it 6 to 1, half dozen to the other?

There is somewhat a redundant cycle in reducing the input at + on the OTA but I would think reducing the current drive, being outside of the feedback loop, would be more direct in affect.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on July 09, 2015, 12:51:58 PM
Not sure if the 2n9001 is part of the bypass as well so I'm hoping someone could explain.

2N9001?

Just this bit is the bypass:

(http://i.imgur.com/p5u3x4G.png)

(Along with the two halves of the DPDT switch, of course.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Cozybuilder on July 09, 2015, 02:05:46 PM
The Millennium bypass needs the LED and load resistor on the drain to function reliably.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 09, 2015, 02:26:28 PM
After comparing the strip board layout with CA3080 (http://tagboardeffects.blogspot.com/2012/11/engineers-thumb.html) I've noticed the following;

- The 2n9001 has been omitted. Is this a bad thing?

- the 1k and 10n on the input has been switched around. Don't think that's a big deal. Maybe has to do with not using the protection LEDs.

- Millennium bypass variant has been omitted.

After comparing the ICs (CA3080 and LM13700) I've drawn this up and believe that the connections are fine.
(https://dl.dropboxusercontent.com/u/91866359/ICS%20PIN1.png)

So why are people still using the LM13700? Does it come down to price and availability?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 02:33:28 PM
The LM13700 is like $1.10

vs. 2 x $2 for CA3080's... that's the way I see it anyway.

MC
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: armdnrdy on July 09, 2015, 02:44:39 PM
The LM13700 is like $1.10

vs. 2 x $2 for CA3080's... that's the way I see it anyway.

MC

The way that I see it is....the CA3080 has become a target for relabeling.
There are a lot of counterfeit 3080s running around out there.
Check the pinout of a single op amp to the 3080. Your circuit will pass signal, seem to be working but...it's actually not.
The suppliers that have actual 3080s have raised the prices dramatically.
I have yet to hear of a relabeled 13600/13700.

Edit:
You might find this useful.
http://www.diystompboxes.com/smfforum/index.php?topic=105341.0
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 09, 2015, 02:55:33 PM
I'm definitely going to draw up and test out this Engineer's Thumb with a CA3080 and a TLO74. More trace work designing probably but should take up less board space. I do plan on adding attack, release and treble boost switch to my project. Not threshold though - Merlin states a few times it functions the same as Ratio. Then I'll have Groovenut beat for design  :icon_twisted:

I'm only teasing. Beautiful work by the way, Groovenut. Very impressive. Nice site as well.

(http://lawrencepetrossdesign.weebly.com/uploads/3/1/4/1/31412717/8404239.jpeg)

The way that I see it is....the CA3080 has become a target for relabeling.
There are a lot of counterfeit 3080s running around out there.
Wow I didn't know that was a thing - counterfeiting ICs lol...
I was going to purchase at least one from smallbear I'll try contacting Steve to see if he has anything to say.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 02:55:40 PM
The "counterfeit" CA3080's I was getting were OK until about 6 months ago.

Now they sound like CRAP.  Noisy, unusable.

I have tried about 3 or 4 different sources.  All bad.  I posted about this a couple months ago.  You can get NOS ones for about $5-$6 each.  But, they are just priced out of the market at that level.



Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: armdnrdy on July 09, 2015, 03:04:23 PM
Wow I didn't know that was a thing - counterfeiting ICs lol...
I was going to purchase at least one from smallbear I'll try contacting Steve to see if he has anything to say.

Steve's will be good. He's privy to the scams. I'm sure he tests them.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 03:19:48 PM
Wow I didn't know that was a thing - counterfeiting ICs lol...
I was going to purchase at least one from smallbear I'll try contacting Steve to see if he has anything to say.

Steve's will be good. He's privy to the scams. I'm sure he tests them.

Yes.  His will be good NOS pieces.  No problem there!

MC
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 03:35:02 PM
Another metal can NOS equivalent is NTE902.

MC
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: armdnrdy on July 09, 2015, 03:41:53 PM
Another metal can NOS equivalent is NTE902.

MC

Yeah but....that part seems to average about $18+  ;)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 09, 2015, 06:27:43 PM
Another metal can NOS equivalent is NTE902.

MC

Yeah but....that part seems to average about $18+  ;)

Just sayin'!

I've stumbled across a few cheaply..  :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on July 10, 2015, 12:17:31 AM
Metal vs plastic: it is the SAME chip inside.

When chips cost $50 each, and went mostly to the military, it made sense to use metal cans and proven (tube-era) metal-glass seals. But plastic is so much cheaper, and in the 1960s TI was making many million plastic transistors for commercial computers with excellent track record. Old habits linger and so did metal-cans, but you absolutely can use one for the other in any on-earth application.

"Counterfeit" is often not a work-the-same chip but a work-"sorta" chip with the factory markings washed off and new marks applied. Like if I got a KIA and pried-off all the bages, put Acura badges on. An innocent buyer might not know the difference- it starts it runs etc. Except Kia/Acura, the fenders are different; most chips are all-the-same except the badging. Parts-marking machinery is very readily available in any electronics neighborhood (mostly China these days). When '3080 went out of production and retail prices rose, some clever sneaks saw an opportunity. Especially since many '3080 builders do not build right away, or are newbies who won't be able to trace their failures to a bogus chip. And there are a few '3080 uses where an op-amp will "work OK"-- just not in any gain-control application. So the eBay hawks are betting they can buy 10-cent chips, mark them for 1 cent, sell them for a dollar, and come out ahead even if some buyers get wise and complain.

I've seen several builds here, even from Known Name kit-stores, which didn't work until a GOOD '3080 was tried.

> His will be good NOS pieces.

AFAIK, Steve is preparing to transition from verifiable odd-lot NOS to new-made on original masks and low-tech processing. ('3080 was low-tech when new and is very training-edge in today's semiconductor word). There are operations like Rochester who specialize in keeping old-old chips in-stock as global demand falls from millions to thousands to hundreds, and even new-make them 1,000 at a time if they think they will sell them over a few years. Steve of course has a very clear idea of the pedal-parts market for '3080s and can encourage or front-money Rochester if that is what has to happen.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: italianguy63 on July 10, 2015, 01:41:11 AM
Metal vs plastic: it is the SAME chip inside.

Exactly, Paul.  No problem getting the plastic "counterfiet" Chinese (good/working) versions of the DIP CA3080 for $1.50 to $2.00 if you shop.  I've just quit fighting it, and have given up on the metal (CAN) versions for now.

I still think, in this context, why use two ($2x2) CA3080's when just one 1st grade (Mouser) ($1.50) LM13700 will suffice?!

(http://i800.photobucket.com/albums/yy286/italianguy63/CA3080_zpsepkwtven.jpg)

A bunch of NFG CA3080 CANs.  A couple DIPs and a NTE902 looking on:

I've wasted a lot of my time on this...


MC
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 10, 2015, 04:11:58 AM
I'm thinking since I'm into more subtle compression the increase in threshold should  get me where I want. Question though, increasing the 1k on the emitter would reduce current to the OTA therefore decreasing the output of the OTA via control current whereas increasing the 10k at the + input of the OTA would reduce the output via less input, both resulting in more overall output level, however will the method used change the outcome or is it 6 to 1, half dozen to the other?

There is somewhat a redundant cycle in reducing the input at + on the OTA but I would think reducing the current drive, being outside of the feedback loop, would be more direct in affect.

I would imagine from a signal-to-noise perspective, reducing the current into the bias pin would be prefereable. Also, I suspect Merlin spent a good while deciding on the 10k/220R divider into the op-amp to maximise the clean headroom.

As far as CA3080 vs LM13700.
They are not entirely equivalent, but are interchangable in some designs including the ET. Personally, I would keep the 3080 for older designs that rely on mojo, like a Ross/Dynacomp. Also, the layout may not be any smaller using a 3080, as you can push the 13700 to the edge of the board and route everything to one side.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 10, 2015, 08:11:26 AM
As far as CA3080 vs LM13700.
They are not entirely equivalent, but are interchangable in some designs including the ET. Personally, I would keep the 3080 for older designs that rely on mojo, like a Ross/Dynacomp. Also, the layout may not be any smaller using a 3080, as you can push the 13700 to the edge of the board and route everything to one side.

If they are interchangeable without any discrepancies for the ET then it would make sense to use the smaller IC. I can understand how using the smaller version of the LM13700 as most people in this thread has is an ideal option but lets say someone with some sort of "healthy" OCD -lol. For me it's about consistency and eye appeal even though the circuit is hidden in a box. If I can get away using a CA3080 (8 pin) and a TL074 (14 pin) I see that being a great/practical choice. I'll report back with my findings soon.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: armdnrdy on July 10, 2015, 09:58:27 AM
As far as CA3080 vs LM13700.
They are not entirely equivalent, but are interchangable in some designs including the ET.

The LM13700 is nothing more than a dual 3080 with a darlington buffer and linearizing diodes in a DIP16 package. If you do not connect the buffer and diodes...you have a 3080.

The design story here:
http://www.idea2ic.com/LM13700.html

Now if you were to sub two 3080s for a 13600/700, you would need to check the connections in the circuit and add a buffer and/or linearizing diodes if those are being used.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 10, 2015, 10:26:03 AM
The LM13700 is nothing more than a dual 3080 with a darlington buffer and linearizing diodes in a DIP16 package. If you do not connect the buffer and diodes...you have a 3080.

This is mostly true, but take a look at the data sheets. The amplifier bias is set up differently such that this pin sits 1 diode drop above V- for the 3080 and 2 diode drops for the 13700. This makes a difference in some applications, but the ET uses a fairly sophisticated precision current source to drive the amp bias, which makes it immune to the voltage on the bias pin. Also, while the ET doesn't use the linearising diodes (not sure how you would add these externally) and output buffer, many applications do.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 10, 2015, 10:27:07 AM
If they are interchangeable without any discrepancies for the ET then it would make sense to use the smaller IC.

It would make sense to you. Not so much to some others.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: armdnrdy on July 10, 2015, 11:19:13 AM
You are correct Sam.

Looking at the 3080s amp bias input, the diodes anode is connected to the base of the input transistor....where as the 13600/700 is connected to the emitter making for two diodes in series.

Adding linearizing diodes to a 3080 would be fairly simple.
The cathode of one diode is connected to the inverting input.
The cathode of a second diode is connected to the non-inverting input.
The two anodes are connected together making the diode bias input as in the 13600/700.

Now...I don't know why anyone would do that when you could just use a 13600/700 except in tight layouts.
While researching the 13600/700 to 3080 daughter board...I did come across a 3080 to 13600/700 daughter board. I guess the individual that worked up that conversion had a truckload of 3080s!  :icon_lol:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 10, 2015, 11:52:45 AM
I've compared this daughter board (http://2.bp.blogspot.com/-P7jqffl_ejk/UHVUB0pXl-I/AAAAAAAAC-k/p2HwRW-52S0/s1600/LM13700+Daughterboard.png) with Merlin's 1st layout(2nd post) which is why I drew the IC schematic on top of this page. The conversion is simple when using for the Engineer's Thumb.

If they are interchangeable without any discrepancies for the ET then it would make sense to use the smaller IC.

It would make sense to you. Not so much to some others.

Regarding the Engineer's Thumb I can not agree with your reply. For this project they seem to work 100% the same with 100% the same results. For other applications I however do understand your point. I've said "interchangeable without any discrepancies". If I'm missing something please elaborate.

I'd rather not work on an inferior compressor which is why I've been barking up this tree. Also - 2 of 8 pins unused apposed to 10 of 16. I sense some practicality here.

That's all I'm getting at.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 10, 2015, 12:04:00 PM
>For this project they seem to work 100% the same with 100% the same results.

I don't think anybody has said that, but rather that the 3080 can be used - I would imagine the noise and overload characteristics are not 100% identical.
This might seem overly pedantic, and perhaps it is. In any case, go ahead and use a 3080. I bought a bunch of these some years ago and am waiting for the price to go up before selling them off - the more demand for them the better.


Larry - your probably right about using external diodes, but you won't get thermal compensation, which probably doesn't matter. I wonder if anybody has tried this with a 3080 or similar.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 10, 2015, 12:05:33 PM
A previous question of mine has been overlooked I hope someone can shed some light.

This strip board layout (http://1.bp.blogspot.com/-mkVcXGZBiYk/ULIlTcwbLbI/AAAAAAAADeI/P3kTBT5XUO0/s1600/Engineers+Thumb.png) has omitted the 2n9001. Would this be a problem? What purpose does this diode in it's position serve?

I would imagine the noise and overload characteristics are not 100% identical.
Thank you for elaborating.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on July 10, 2015, 12:24:10 PM
Do you mean 2N7001 - an alternative to the BS170 on Merlin's schematic?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slacker on July 10, 2015, 12:25:51 PM
This strip board layout[/url] has omitted the 2n9001.

The missing diode is for power supply reverse polarity protection, providing you don't reverse the power then you don't need it and it does nothing :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on July 10, 2015, 03:24:50 PM
Do you mean 2N7001 - an alternative to the BS170 on Merlin's schematic?
I meant the 1n4001. Sorry I have way too many part numbers zipping in my head as of recently lol.

The missing diode is for power supply reverse polarity protection, providing you don't reverse the power then you don't need it and it does nothing :)
Thank you very much. I should have guessed.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 09, 2015, 01:13:46 PM
Hey guys I'm back!

After a few bread boarding fails and many distractions I've decided to try again last night with some success.

EDIT: Fixed some connections and now compression is very noticeable. Sometimes too much compression when ratio is cranked. Only issue now is a gaining buzz when I'm not plucking any strings. I'll start from scratch again and see what happens.

I've learnt that pretty much all all controls (minus the compression (ratio) could be better set as mounted trimpots. Attack, decay and level if desired. A 1 knob compressor sounds more practical anyhow seeing how there isn't much range or use with additional 3 controls + volume.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 09, 2015, 01:56:11 PM
take a feed from Pin 7 of IC2 (the opamp connecting to the PNP), hook it up to the Base of a NPN, and wire V+ through the Collector and LED from the Emitter for a simple-yet-handy compression indicator. score!

Just found this on page 8. I'll give it a shot - I hope it does what I'm looking for reliably. We'll see tonight!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 10, 2015, 12:02:57 PM
I've tried the LED method I've quoted and did not have much success. It resulted in more noise and popping. I've tried different variations thinking maybe I misunderstood the connections with no luck. Had better results with B on the - instead of output but it's not stable or consistent.

Can someone please validate this picture for being a correct interpretation?
take a feed from Pin 7 of IC2 (the opamp connecting to the PNP), hook it up to the Base of a NPN, and wire V+ through the Collector and LED from the Emitter for a simple-yet-handy compression indicator. score!

Any ideas?
So the ouput of that opamp to B of a NPN. Simple enough.
(https://dl.dropboxusercontent.com/u/91866359/ET%20LED.png)

Ehh I'll keep at it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on September 10, 2015, 05:20:33 PM
I've tried the LED method I've quoted and did not have much success. Can someone please validate this picture for being a correct interpretation?
You'll need a resistor (e.g. 1k) in series with the LED. As shown it should go dimmer when there is more compression, although it sounds like you still have issues with the actual audio circuit (?)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 10, 2015, 05:55:38 PM
Yeah there's something connected wrong and I can't spot it.
-The bread boarding life...

After I posted that diagram I found yours on page 9 with the 470r to vb. I've gotten results close to what you've described but a little finicky. I'll report back with a sample of the sound and the LED in action when all is well.

Thanks for the awesome compressor Merlin  :icon_biggrin:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 10, 2015, 10:02:38 PM
> the ouput of that opamp to B of a NPN. Simple enough.

That won't work. The LED is always-on and carrying infinite current. Also fouls-up the compressor.

There's a simple linear-proportional way to add an indicator. See the BC327 PNP and 1K resistor? This flows a current proportional to over-level, and closely related to amount of gain reduction. That current is weak and already committed to tickling the LM13700. But we can take the same Base signal, to a second PNP, with a smaller resistor, and get a proportionally larger current we can dump to an LED.

(This form of "current mirror" has a small 40mV mirror-error which is totally moot for a visual indicator.)

(http://i.imgur.com/IXLn0BP.gif)

The light happens when the compressor is "doing something", which makes sense to me. If the LED is off, it is just a buffer/booster. When signal gets loud, so that the sidechain tickles the '13700 to turn-down the signal, the LED turns-on and gets brighter.

For bench-test only, you can put your volt-meter *across* that 1K resistor. Use a 2V range (auto-ranging may be confused by dynamic guitar signals). The DC voltage is zero for no- or small-signal. When signal is excessive, voltage will increase to 1V (maybe a bit more or less), fading back to zero as the note decays.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 12, 2015, 05:51:14 PM
The PNP idea worked although the LED slowly dims out at a constant rate. It does light up accordingly with the expected amount of compression. There may be an issue on the bread board still. It's obvious that as the LED dims out there's a slowly amplifying noise as there was before. Perhaps the 3080 I'm using is faulty. I'll keep at it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 12, 2015, 06:24:17 PM
> the LED slowly dims out at a constant rate. It does light up accordingly with the expected amount of compression.

What it probably should do *with guitar*. Guitar plucks, big start, heavy compression. Guitar fades-out, compression releases. The guitar fade-out is not "constant", depends on what strings (speaking length, gauge) and how solid the axe is; but for musical reasons the fade-out is in a narrow range.

Compare to piano, upper octave just goes "Tik", or organ which can go on forever.

So what is your present problem? (Too many pages to go back through.)

> Only issue now is a gaining buzz when I'm not plucking any strings.

The no-signal gain of this compressor (most guitar compressors) can be very high. This WILL amplify ALL the hum and buzz in the room (also hiss in the amplifier).

If you are "on breadboard", and it passes signal, and squashes, and the only problem is hiss/buzzz/hash when it goes to idle, what you need is a closed metal enclosure to keep the crap out. Time to box it up. Even if only in a bread-pan as a quick-check before you drill/polish/paint something nice. (If you have a battery power amplifier and can run the breadboard on a battery, take it out in the middle of the lawn. Not under the power-line like my lawn.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on September 12, 2015, 07:57:16 PM
Thanks for all the info I appreciate it.

What I mean by the LED slowly dimming is if I do a hard finger pluck and mute it quick the LED still slowly dims out even when I mute the strings so they aren't ringing out. The longer or continuous I pluck the strings or really rail on some chords it actually effects how long it takes for the LED to start to fade out again. Like it's stuck on for a long while then finally goes out. And when it does fade it amplifies any noise. If the LED is acting with the compression then something is surely out of whack if it's compressing for a way longer than than it should. I'm hoping it's not the 3080 since I was hoping to use it for the final board. I'll try the bread board again and with a switch between the 3080 and a LM13700 just to see what may happen if anything at all.

These single coils aren't really quite anyway but I do believe something isn't right here beyond interference. We'll get to the bottom of it. I'll start working on a PCB and have it pretty and boxed up come next weekend.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 12, 2015, 11:31:29 PM
> mute it quick the LED still slowly dims out even when I mute the strings

Ah. That is also expected. A very sudden return to high gain would "breathe", pump-up the hiss too fast, as you have noted. All audio compressors have a "release" time-constant. Here it is the two 1uFd caps and the 1Meg bleed resistor, around 2 Seconds. In "normal" guitar use, the string fade-out is about this long, a good fit. If you instant-mute, you get a second or two of slowly-rising gain before the hiss comes back up. Used appropriately, the compressor brings-up the decaying tails of the notes, but if done too much the rising hiss is a problem.

Just for the experience, tack-solder a 47K across the 1Meg that comes off a 1uFd cap. That gives a good short attack. So short it may only be good for a military intercom, where we need "every syllable" at FULL loudness. Or maybe drums. 200K or so may be better for other music.

The perennial curse of compressors is that they help with old problems (overload, uneven levels) and introduce new problems (moosh, pumped hiss). It takes time to dial-in an acceptable amount of compression.

> hoping it's not the 3080

There ARE bad '3080s but they usually don't work at ALL. Some fraudster re-marks opamps or logic chips, they don't pass audio and generally show way-wrong DC readings. If it is changing gain I'd be real confident of the '3080. Solder, wiring, value, or soldering mistakes remain popular problem.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: electricco on October 10, 2015, 05:04:39 AM
I built it and... WoW !  8)
Super compressor, the best stomp comp I ever used so far. Really good job Merlin !!!  ;)

I built the 5 knobs one and in some settings I can recreate either CS3 or dynacomp sound as well  :icon_twisted:

the pro is the versatility of this stomp, but at the same time in some settings there is no musical application range...
I think 510Kresistence + 500KB Pot will be better for release POT ( in some setting 1M will make sort of volume swell)

I think also Ratio+Threshold should be limited as well.. but I do not know well the right mod for these (any suggestion is welcome!)

What I feel the need for is a tone Control (the bright switch works but not enough), using it for the arpeggio in 1° position on Guitar bass chords there is too much loss of high.
Can the bright switch turned into a tone control in style of TS9 or similar ? (changing the resistor with a pot)
Or can be used the other OP of LM13700 for tone purpose (if so, how...  :o ) ?

Thanks again for sharing!!
Looking forward for any suggestion.





Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on October 16, 2015, 08:20:12 PM
Hi all,
I ordered the parts for the ET a while ago and I'm looking forward to building it, but now I've seen the GTi version! Is there a vero layout for the new version floating around anywhere?
Cheers
Pat
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on October 19, 2015, 05:51:25 AM
Can the bright switch turned into a tone control in style of TS9 or similar ? (changing the resistor with a pot)
You could replace the 10k resistor (the one in series with the 4.7n tone cap) with a pot wired as a variable resistor. 47k or 100k would probably do. Maybe with a 1k to 5k resistor in series with it, to limit the range a bit -you'll have to experiment.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on January 03, 2016, 04:20:05 AM
Hi again,
A simple question to begin with - to add a threshold control to the GTi, would I just replace R10 with a 1M log pot?

Now the other questions, first about the LED bar graph display - is it possible to quantify the amount of compression at each step? I like to put numbers on things :)
The TI datasheet (http://www.ti.com/lit/ds/symlink/lm3916.pdf) has a table on page 4 showing threshold voltages and signal strength, but I'm not sure how to translate it to "dB reduction" for a compression meter. The LM3915 might be easier to implement, since it's 3dB per step. The 3915 is easier for me to get a hold of, too, which is a bonus.

Speaking of putting numbers on things, is there an easy way to work out some values for the attack, release, and ratio at various stages of pot rotation? It wouldn't be too tricky to do in a DAW after I've built it, but if there's a way to work it out beforehand that'd be great.

Cheers
Pat
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 04, 2016, 11:33:36 AM
Hi again,
A simple question to begin with - to add a threshold control to the GTi, would I just replace R10 with a 1M log pot?
Which schem version are you referring to? I recommend a linear pot, rather than log.

Quote
Now the other questions, first about the LED bar graph display - is it possible to quantify the amount of compression at each step?
I don't think so, because the numbers will be different depending on the ratio setting. It's so long since I did this that I can't even find the GTI schematic! But I think the bar graph gives only a relative indication between no compression and max compression, whatever max happens to be for that ratio setting.

Quote
Speaking of putting numbers on things, is there an easy way to work out some values for the attack, release, and ratio at various stages of pot rotation? It wouldn't be too tricky to do in a DAW after I've built it, but if there's a way to work it out beforehand that'd be great.
Hmm, I doubt you can do it in advance. The attack/release times are somewhat non-linear (incalculable) owing to the type of precision rectifier. I think you'll have to measure it the old fashioned way!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on January 04, 2016, 04:53:43 PM
Thanks for the feedback, Merlin :)

The schematic is in the pdf posted on page 8 of the discussion:
Would u be so kind to share the 2 layer 5 knobs PCB layout here ? Thank you in advance.  ;D
Here you go, a single-sided version:
https://dl.dropboxusercontent.com/u/57831278/115x60mm.bmp
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf

If the bar graph is just a relative indication, I'll probably go with the LM3915. That'd produce a display that's less detailed when the signal's being compressed the most, but should have ever so slightly better resolution when the signal's just starting to become compressed. All academic, really, though.

Good to know about the attack/release times, too. It'll be easy to do some measurements after it's built. I'll probably just get distracted and start playing, though :D
Cheers
Pat
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Hatredman on January 05, 2016, 10:34:28 AM
Hey, Merlin, did I miss something?

(http://i.imgur.com/9rU9vCE.png)
merlinb
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on January 05, 2016, 02:15:35 PM
Try this one: http://www.valvewizard.co.uk/engineersthumb.html (http://www.valvewizard.co.uk/engineersthumb.html) :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on January 30, 2016, 11:10:48 PM
Howdy gang, having issues with my circuit. I'm getting no output signal, it's dead quiet. I built it on Merlins PCB layout and the etch turned out quite well.

Images are below.

Voltages as follows (from 9.37V~ supply):

U1
1. 4.68
2. 4.68
3. 2.34
4. 0.00
5. 2.34
6. 4.69
7. 4.69
8. 9.37

U2
1. 4.2
2. 4.68
3. 2.35
4. 0.00
5. 3.13
6. 4.69
7. 4.69
8. 9.37

U3
1. 1.08
2. 0.00
3. 4.69
4. 4.69
5. 4.69
6. 0.00
7. 0.00
8. 0.00
9. 0.00
10. 0.00
11. 9.37
12. 0.00
13. 0.00
14. 0.00
15. 0.00
16. 0.00

Q1
e. 4.68
b 4.19
c 1.1

(Substituted 3mm LEDs for 5mm, BC327 for 2n3906, 47u power supply filtering is tantalum, 100n and 4.7n caps are ceramics due to tight PCB spacing, ICs are soldered because I'm an idiot ;) )

(https://36.media.tumblr.com/af8dfc4c303c8491af92c0df6e28efe1/tumblr_o1stw723Mf1qkzl6yo1_540.jpg)
(https://41.media.tumblr.com/15449c13c261f71e0be004613a8f8ff8/tumblr_o1stw723Mf1qkzl6yo2_540.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on January 31, 2016, 05:21:31 PM
there's not that much of audio signal path, but have you tried ye olde audio probe, starting at the input jack, moving along each junction? the voltages seem ok at a glance
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on January 31, 2016, 06:23:22 PM
Yeah hmm, I will give ye signale proybe a go later (at least properly). It seemed to stop before the transistor, at last check. Also it's very distorted at pin 5 of the LM13700 and cleans up when I turn the ratio down, hm. I get nothing at the level pot which rules out the millenium bypass being an issue (at this stage anyway). I couldn't find 'proper' voltages anywhere online, but if you say they seem ok that's good!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on January 31, 2016, 06:45:47 PM
by "audio signal path" i mean from the input jack to the 1kΩ resistor, the 10nF capacitor, the non-inverting input of U1A, the output of U1A, that 10µF capacitor to the following 1kΩ resistor to the 10kΩ pot, to the output jack. not all that much point in audio probing the rectifier. that does sound kinky, though.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on January 31, 2016, 08:01:27 PM
Yeah I didn't think it had anything to do with the audio path... lol. Ok. I'll look at it tonight after work. Thank you my friend  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Beo on January 31, 2016, 09:32:08 PM
not all that much point in audio probing the rectifier.

Heh, that's a good one!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on January 31, 2016, 10:47:59 PM
I'll bloody probe your rectifier if you're not careful. JUST KIDDING. Thank you for the advice and yes, I am a noob.

I just got the point of rectifiers.. they convert your guitars AC signal into DC so it can change the gain or something right?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on January 31, 2016, 11:21:52 PM
> the point of rectifiers..

Audio swings both ways, constantly.

The gain-control element wants a one-way signal, not changing (well, changing slowly with loudness, not with every individual swing of the string).

Rectifiers can convert the both-ways audio into a one-way signal.

There's a capacitor somewhere to smooth-out the individual string-swings into a steadier gain change signal. (Actually two smoothing caps.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on January 31, 2016, 11:53:45 PM
So the 1uf caps remove the AC-ness to give it steady DC.

U1A is audio path amplifier, and U1B is for the gain control part. Ok I found your walkthrough of the circuit from page 2! Very helpful Mr PRR. :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on February 01, 2016, 05:34:53 AM
Voltages look OK, and I can't see any incorrect parts in the photo. This suggests to me it may be something that is not in the photo. Input/output wired up correctly?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: chuckd666 on February 01, 2016, 08:06:17 AM
Hello everyone! I have worked out my issue. As always, it was a few weak traces which were not giving continuity. Duh. I think it's all good now, very compressy! At full output I'm just under unity - is this normal?

Thank you all for your help so far! You're all very lovely and patient.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: electricco on February 19, 2016, 12:24:22 PM
Hi, I built it (5 pots and 1 switch) but has an issue.

There is a ramp into the output volume  (from low to hi).
It's happened with any pots regulation...
I've already changes all the IC but nothing.

What I should look at ?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on February 22, 2016, 05:19:35 AM
There is a ramp into the output volume  (from low to hi).
Can you describe this symptom in more detail?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: 287m on April 07, 2016, 05:39:22 PM
hi folks
i just chat with friend, and in middle conversation he say want engineer thumb (again)
he build 2 knob from merlin pdf, he just want add knob but dont want build GTI version
so he redraw schematic like this, no treble boost
(https://2.bp.blogspot.com/-xTUmn1pjtjQ/VwbR-NUsfeI/AAAAAAAAAI8/-dAtS4-omlMmgq5b-ZL0mw-kgD2ibXIKQ/s1600/engineer-thumb.png)
so, before i make layout and buy part. just need correction and suggest mods. hehe
Thanks

Febri
===
oh i love edit function in this forum
assume above schemo is right, then he good solderman, and i am big fans of sijosae
here the prev for onboard pots and led in perf https://1.bp.blogspot.com/--Rr1afqCEUo/Vwb9D1LhGuI/AAAAAAAAAJM/sbAj_egsspAI3le6g5Bpfpl4gYX09TC5A/s1600/et.png (https://1.bp.blogspot.com/--Rr1afqCEUo/Vwb9D1LhGuI/AAAAAAAAAJM/sbAj_egsspAI3le6g5Bpfpl4gYX09TC5A/s1600/et.png)
the moral today, dont say 'I Can' as fast before think when your friend request all onboard in 1590A!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Hatredman on April 07, 2016, 07:24:39 PM

There is a ramp into the output volume  (from low to hi).
Can you describe this symptom in more detail?

I guess he meant that the attack is reeeeeeeeeal slow.


Sent from my iPoor using Tapatalk - now Free because I'm poor
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on April 29, 2016, 10:22:38 PM
Someone on Madbean was having trouble with an added threshold control, and I noticed that the usual suggestion seems to be to replace the 1M with a pot wired as a VARIABLE RESISTOR. There's a bunch of reasons that doesn't work well. I popped over here to suggest, or clarify (Merlin's intention wasn't entirely clear from the graphic on the original schem) that it should be a VOLTAGE DIVDER instead.

It looks like 287m, or his friend who re-drew the schematic he posted, got it right. Just to clarify, if it's a variable resistor instead of the voltage divider, the input impedance drops and the only reason you get a lower threshold is because you're losing signal.

Still probably not worth including the threshold control given the way the design works, but I thought it was worth pointing out.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Yazoo on June 13, 2016, 12:33:10 PM
I built this a while ago using the Valve Wizard pcb, the original two pot version Unfortunately, I have not been able to get this working properly. I get a drastic volume drop when the effect is on with the ratio pot turned fully up. I have been trying to debug it but I can't find any mistakes, though I must have done something wrong. :icon_confused:

These are my voltages:

U1
Pin 1 4.5 V
Pin 2 4.47 V
Pin 3 3.9 V
Pin 4 0
Pin 5 3.9 V
Pin 6 4.47 V
Pin 7 4.55 V
Pin 8 9 V

U2
Pin 1 3.89 V
Pin 2 4.45 V
Pin 3 3.9 V
Pin 4 0
Pin 5 4.17 V
Pin 6 4.48 V
Pin 7 4.48 V
Pin 8 9 V

U3
Pin 1 1.19 V
Pin 2 0.73 V
Pin 3 4.48 V
Pin 4 4.48 V
Pin 5 4.48 V
Pin 6 0 V
Pin 7 0 V
Pin 8 0 V
Pin 9 0 V
Pin 10 0 V
Pin 11 9 V
Pin 12 0.6 - 1 V
Pin 13 0.7 - 0.86 V
Pin 14 0.52 V
Pin 15 0.77 V
Pin 16 = V

Q1 C 1.18 V
     B 3.9 V
     E 4.45 V

I used a signal generator and oscilloscope to try and trace the signal through. The output on U1 pin 7 to the two diodes looks clipped and healthy but there is no signal after D1 and I can't see anything going into pin 3 of U2.

Any advice would be gratefully received, thanks.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on June 13, 2016, 04:05:58 PM
Still probably not worth including the threshold control given the way the design works, but I thought it was worth pointing out.

Hi Midway,
Just wondering what it is about the design that means the threshold control isn't really worthwhile. I'm planning to build the gti version and was going to add a threshold control; I most likely won't now, but I'm interested to know more about the circuit.
Cheers
Pat
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 13, 2016, 04:27:20 PM
there is no signal after D1 and I can't see anything going into pin 3 of U2.
Are you using DC coupling? You should see the DC go up and down in sympathy with the audio amplitude.

All your voltages look right except:
Quote
U2
Pin 1 3.89 V
Pin 2 4.45 V
Pin 3 3.9 V
Is this with a signal applied or not? With no signal I would expect pin 1 (Q1 base) to be closer to 5V (i.e. above the emitter). If the transistor is being held 'on' this could explain your volume drop... Is D3 the correct way around? Is R15 definitey 1Meg?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 13, 2016, 04:30:28 PM
Just wondering what it is about the design that means the threshold control isn't really worthwhile.
Basically because it is soft-knee compression. When you're operating in and around a soft knee, turning down the threhold has a very similar effect on the transfer function as as turning down the ratio. You can see that to the left of the red line (i.e. around the knee) both graphs look very nearly the same, so if your signal spends most of its time in this region, you won't notice the difference between using the threshold control or the ratio control.
(http://i81.photobucket.com/albums/j207/merlinblencowe/text3940_zpsx4vqiaem.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: patricks on June 14, 2016, 03:04:48 AM
Excellent, thanks! :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Yazoo on June 17, 2016, 08:09:49 AM
Thanks for the suggestions. I checked and the resistor is 1M and the diode is the right way around. I've done the usual and scratched around the pcb to check for shorts but I couldn't find anything. I've swapped out the ICs just in case.

I am still getting a slight voltage/volume drop when I apply a test signal, a sine wave, with the ratio pot turned up and the level pot full on. With the ratio pot turned down and the level pot full on, the signal is at about half strength. I am just seeing a standard sine wave on the oscilloscope.

I should admit at this point that I really enjoy building but I don't really understand how the circuits work. Should I be seeing an AC wave on the oscilloscope after D1?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 20, 2016, 05:39:12 AM
With the ratio pot turned down and the level pot full on, the signal is at about half strength.
When you say 'turned down' do you mean higher resistance, or lower? How big is your input signal? It may be that the effect is working normally and what you're seeing is the compression. Try turning down the input signal level to 50mVpp -does the output signal amplitude then start to match the input signal?

Quote
Should I be seeing an AC wave on the oscilloscope after D1?
No, you should see DC, although it may be wobbly DC.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Yazoo on June 20, 2016, 04:47:48 PM
Many thanks! I had one last go and swapped out the LM13700 with yet another chip and it now works. So that's two dud LM13700s.  :icon_evil:

There is no problem with the volume now.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MC-Sammer on September 04, 2016, 06:33:50 PM
I'm having some trouble getting this working; I'm attempting a 4 knob version (Attack 100k, Release 1M, Ratio 1M and Level 10K) with a layout of my own design.

The issue I'm noticing right now is that I can't turn the Ratio knob below 967K without getting clipping on the output, and if I go much higher than that there is no output at all.

Here are my pin outs for an equivalent TL074 based circuit http://jmkpcbs.com/wp-content/uploads/2014/08/Engineers-Thumb.pdf  (All controls maxed /w 100mv 1KHz input):
1: 4.96
2: 4.85
3: 4.46
5: 4.46
6: 4.53
7: 8.25
8: 6.30
9: 4.66
10: 4.44
12: 4.31
13: 4.53
14: 4.53

And the Output that is buffered by the LM13700 when ratio is set to min:
5: 4.47
6: 4.85
7: 4.85

I'd post my layout, but the attachment option isn't showing up for me; perhaps I don't have enough posts yet :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on September 05, 2016, 03:01:26 AM
Looks like you have no ground connection.  Check your wiring and/or soldering.

There is no "attach".  You need to have your pictures hosted somewhere in web-land (e.g. imgur), then embed using the Mona button (http://www.diystompboxes.com/smfforum/Themes/DIYTheme2/images/bbc/img.gif) and the URL of your hosted picture.  (Hit "Quote" to see how I embedded the Mona icon.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MC-Sammer on September 05, 2016, 04:06:32 PM
Looks like you have no ground connection.  Check your wiring and/or soldering.

There is no "attach".  You need to have your pictures hosted somewhere in web-land (e.g. imgur), then embed using the Mona button (http://www.diystompboxes.com/smfforum/Themes/DIYTheme2/images/bbc/img.gif) and the URL of your hosted picture.  (Hit "Quote" to see how I embedded the Mona icon.)

I checked my wiring and did find that I missed one cut , putting the 4.5 bias on the OTA side of the 1K going towards the inverting input of the output opamp.

I've fixed that, but it still appears that the gain of IC1 is driving the output into clipping. It also does that when I have the LM13700 removed... Not sure what to make of that.

(http://i.imgur.com/EOoUEko.png)

Ignore the board on the right, I was using it to spot check the cuts on my board.

Also, the OTA bias line from the transistor looks confusing, but I'm just stretching the collector over the bias line and soldered it right into the bias.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: MC-Sammer on September 15, 2016, 09:12:59 PM
For anyone who is curious, I think I narrowed it down to an issue with the 4.5V bias on the input opamps; now to track down the cause :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slashandburn on November 06, 2016, 04:20:08 PM
I've found a board for this amongst my bits, it seems I must've etched Jon Pattons compact layout some while ago and then and then chickened out from building it. I'm going to give it a go soon.

I can't seem to find it in this thread, I'm sure it's buried here somewhere. Here it is for reference.
(https://s13.postimg.org/9is4w7ymr/ET_1590a_final_1.jpg) (https://postimg.org/image/9is4w7ymr/)

Looks like more of a challenge given that the components aren't numbered on the valve wizard schematic and I'd need to work a bit to work out whats going where.  Thought I was up for it. Fell at the first hurdle.

There are two pads underneath the IC labelled U3 (on Jons pcb layout). I'm guessing I leave them blank and probably shouldn't have bothered to drill them, but then I can't work out why they'd be there. 

A little help, please?




Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on November 07, 2016, 03:21:46 AM
Looks like more of a challenge given that the components aren't numbered on the valve wizard schematic
There is a numbered schematic here. It looks like Jon designed his PCB to match, kinda. Looks like U2 and U3 numbers have been swapped though.
http://valvewizard.co.uk/engineersthumb.pdf

Those pads look like surface-mount pads, corresponding to C4 and C5. I'm guessing Jon used surface-mount capacitors on the underside of the board to save space.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slashandburn on November 07, 2016, 07:10:36 AM
Looks like more of a challenge given that the components aren't numbered on the valve wizard schematic
I'm guessing Jon used surface-mount capacitors on the underside of the board to save space.

Oh. Bugger. Thats probably why I abandonned it the first time. I think you're right.  I'm staring at the board and thinking it was intended for a 1590A.  Damn thats a tight looking fit.  I'm neither skilled nor ambitious enough to pull that one off. No idea why I didn't etch the other board.

Thanks man, the numbered schematic really helps!  Doh!    Another coffee or two and I should know whether I'm feeling up to it.    Looks like just those two SMD components at a glance though.

Hmm, so for future reference: pads without drilling holes in the middle, don't drill them?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on November 07, 2016, 09:09:19 AM
Those pads look like surface-mount pads, corresponding to C4 and C5. I'm guessing Jon used surface-mount capacitors on the underside of the board to save space.

It's redrawn using one of my layouts ... I have no idea what those pads are, but I definitely didn't use surface-mounted! slashandburn, my perf layout is somewhere in the depths of this thread, or in the library file linked on my Things I Make page if you need a parts reference.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slashandburn on November 07, 2016, 01:37:16 PM
Nice one thanks! Ill work it out!

Yup, found the original post after a lot of searching, then forgot to bookmark it. I'll have a look again another night, I think I'm short a few parts too.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on November 08, 2016, 03:28:13 AM
Hmm, so for future reference: pads without drilling holes in the middle, don't drill them?
Indeed. However, now that you have drilled them you could use a couple of through-hole disc capacitors. If you fold them over flat against the board then I doubt they'll get in the way (?).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: lars-musik on November 08, 2016, 07:05:15 AM
Hi there,

looks like I've been sleepy lately. I completely missed first the post then the familiarity of the layout. I redraw Jon's layout for a 1590a ET.

Here's the build document:

https://www.dropbox.com/s/g7l603fsgfvsicg/Engineer_final.pdf?dl=0

Yours, Lars
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slashandburn on November 08, 2016, 07:50:52 AM
Hi there,

looks like I've been sleepy lately. I completely missed first the post then the familiarity of the layout. I redraw Jon's layout for a 1590a ET.

Here's the build document:

https://www.dropbox.com/s/g7l603fsgfvsicg/Engineer_final.pdf?dl=0

Yours, Lars

Awesome!  Thanks man, that makes life much easier.    Did you really manage to squeeze it all in a 1590a?   Mad skills.  Way beyond my capabilities.

I have an idea for a prepainted 1590B that should suit this though. If I can get it finished, that is.  Prepare yourselves for more tedious questions from me on this thread over the coming days/weeks/months/years.

Those pads were indeed intended for (SMD?)  C4 and C5 then it seems?  I think I should be alright from there.

Cheers

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: lars-musik on November 08, 2016, 08:29:23 AM
Yes, those two are C4 and C5, both 1µF. Good luck!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DK1 on January 15, 2017, 09:21:59 PM
Finally got it all together tonight. A little trial, and a lot of error, but it sounds great. Thank you!

(http://imgur.com/HNHOKB6.jpg)
(http://imgur.com/00G3n1N.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: blackieNYC on January 16, 2017, 10:29:02 PM
Question - for the four-knob builds.  Is yours behaving a little oddly at shorter release times?  Interesting thing going on.
   If I position the release pot (1M) at around 400K, I get a bit more desired "pop" on each of a sequence notes - as I would expect, because the release lets go quickly and the attack reveals itself.  This is definitely a compressor-as-effect setting.

But the output level is hunting around, skipping around in level. I realize the short release will change things, but this seems excessive. (I've breadboarded this from scratch twice.)    It sounds to me like the circuit is responding to beat frequencies from the chord.  Low ones - 3Hz, 7Hz, I dunno.  My MXR doesn't seem to do this. So I've attempted to filter off the lows from when the input is split off from the audio path to the side chain at p[in 5 of U1B.   
  It appears to be working a bit.  I think?  It makes sense in theory, a little. If the amplitude of the beat frequencies is enough to trip the compressor. Don't you think?  I used a 100K to bring Vbias to pin 5, and a .022uf cap from pin 3 to pin 5.  Does this make sense?
   So does yours do this when the release pot is under 500k or so?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 17, 2017, 06:45:05 AM
But the output level is hunting around, skipping around in level.
I think we need a recording to tell if this is just normal compressor behaviour or a fault.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Koldman on February 26, 2017, 12:11:03 AM
Hi I just built the two knob from the provided PCB. I'm new to compressors and I'm not sure if the way its working is normal. If I play firmly it compresses but then switch to soft picking it takes a while to bring up the volume. Have I made a mistake in construction or is this how it works?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: highwater on February 26, 2017, 08:20:03 AM
Depends on what you mean by "a while".

If it's "a couple seconds" or longer, you might have a bad solder joint around the 1meg "decrease for shorter release" resistor (the number depends on the schematic, it's R12 in Merlin's PDF). That's what happened to me when I put that resistor in the wrong hole on a stripboard build - still more-or-less worked after I fixed my other mistakes, but it took several seconds for the volume to come back up.

Otherwise, might be normal, might not. Somewhere in the last 20-some pages, someone measured and posted the release times with a few different resistor values... I can't remember who/when/what the numbers were. The graph on Merlin's website (http://www.valvewizard.co.uk/engineersthumb.html) looks to show about a 0.7second release time with what I assume is a 1meg resistor.

Unless there is an obvious-in-hindsight soldering issue, try swapping that 1meg resistor for something smaller; I tried 1meg and 470k before deciding to just box mine (eventually) with a release knob, and the 470k was still (as far as my tin ears can tell) a much longer release than an Orange Squeezer (the only other compressor I've used with a guitar).

---

BTW, Merlin, I absolutely love this thing. I can't imagine wanting a guitar compressor that's squishier or quieter... and it'll only get quieter when I get a box for it and it's not a bare circuit board hanging-off my breadboard.

Also, I didn't want to bump the thread for what I'm guessing is a silly question, but I'm thinking about adding a sidechain input when I box it up. I assume that I can just separate the non-inverting inputs to U1a and U1b (numbers from the web-page), add a second 1meg bias resistor, and wire-up a switching jack to connect them together when there's no plug there... anyone see a problem with that approach?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Koldman on February 26, 2017, 10:26:04 PM
I tried to record it, but it didn't come out for some reason, but you can hear the swell when I stop playing at the end.
https://youtu.be/FUnqxVv3jmc
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: highwater on February 26, 2017, 11:15:43 PM
Youtube's compression is masking the effect on the notes I suspect... in any case I can't hear whether that's correct or not, but the swell at the end sounds more-or-less the same as mine. Probably normal.

You could take R12 out and replace it with something smaller -- the lowest setting on the 4-knob version is 220k.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Koldman on February 27, 2017, 05:58:37 AM
I put in a 220k resistor and a 416k trimpot in but I didn't find it hugely useful. I think this just isn't the compressor for me. Thanks anyway!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on February 27, 2017, 08:31:09 AM
I put in a 220k resistor and a 416k trimpot in but I didn't find it hugely useful. I think this just isn't the compressor for me. Thanks anyway!
In that case you won't find any compressor for you, since all compressors have a release time!  :icon_lol:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jfrabat on March 05, 2017, 01:14:27 AM
See, I thought I was building my final pedal, and you all force me to look at this thread!

On a serious note, where's the best place to get the LM13700?  I have not been able to find it locally in Costa Rica, si it is off to the internet!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: davepedals on March 05, 2017, 08:09:35 AM
I'm trying to make a PCB of this, two knob version.  Don't want to use the PDF file because I want to add other PCBs to my transparency sheet. The PDF will not let me copy the PCB image.  Does anyone have an image file of this PCB?
Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on March 05, 2017, 02:49:17 PM
I'm trying to make a PCB of this, two knob version.  Don't want to use the PDF file because I want to add other PCBs to my transparency sheet. The PDF will not let me copy the PCB image.  Does anyone have an image file of this PCB?
Thanks!

How about screen shot and paste to Paint? Then resize to the proper dimensions? Give me a minute though, I'll see if I can extract it with Nitro.

Here you go chief...

(http://i214.photobucket.com/albums/cc196/digi2t/engineersthumb_001_zpsfecl25v2.jpg)
 (http://s214.photobucket.com/user/digi2t/media/engineersthumb_001_zpsfecl25v2.jpg.html)

You can also click on the image and go to Photobucket and download it from there. Let me know if there's a problem.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: davepedals on March 05, 2017, 05:36:37 PM
I appreciate your efforts… I've tried this before however and upon resizing, the image is degraded.  I'm really hoping someone has the original image file correctly sized.  Thanks for the effort.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 05, 2017, 05:41:32 PM
I appreciate your efforts… I've tried this before however and upon resizing, the image is degraded.  I'm really hoping someone has the original image file correctly sized.  Thanks for the effort.
The plain image file is at the bottom of this page:
http://valvewizard.co.uk/engineersthumb.html

You can paste it into a word processor or whatever and set the size.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: davepedals on March 05, 2017, 06:08:02 PM
Thank you, Merlin, that's exactly what I was looking for, a large image that would be scalable without degrading. Can't wait to try his one, I definitely need a new compressor from a rig. This looks like the right one... kudos for the compressor design!
Once again, digi2t,  I do appreciate your effort, however like I said I tried the same thing and resizing may damage too fuzzy.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on March 05, 2017, 07:07:47 PM
No problemo miho. I was just about to tell you to PM merlin, but I guess his ears were burning. :icon_lol:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bean on March 05, 2017, 08:17:33 PM
Hope this isn't too much of a derail: I have a version of the Thumb I made for myself which uses an LM13700 and has external pots for attack, release and threshold. Build is verified with a couple minor caveats. Anyway, I have 5 extra boards I don't need and I'm happy to just give them away. If anyone wants one lemme know.

Build doc is here: http://madbeanpedals.com/projects/Thumb/Thumb.zip

(http://madbeanpedals.com/projects/Thumb/ET_SILK.gif)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: davepedals on March 05, 2017, 08:47:20 PM
I'd certainly take one off of your hands if it's not too late! I'm definitely going to make a PCB for the tuna version, however I would like to fool around this other version as well . I'll PM you my address . Thanks!

EDIT:   tuna version?  Jeeze... I meant 2 knob version. Ha ha!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: davepedals on March 11, 2017, 10:47:44 AM
Hey, Merlin …


 This PCB I got from you... could I just add the ratio and the level and leave the others blank?  I'm just curious really, as I think I'm gonna add the others anyway , nice to know though! And thanks again!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on March 11, 2017, 11:38:37 AM
Quick Q...

I was looking at the GTI version with the bar graph, and was thinking of trying it. Can someone confirm if the LED driver arrangement works?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: adam193 on March 11, 2017, 12:11:37 PM
Im looking to build one of these on stripboard.

The layout is on 20 row, can this be built on 19 row?

(http://1.bp.blogspot.com/-mkVcXGZBiYk/ULIlTcwbLbI/AAAAAAAADeI/P3kTBT5XUO0/s1600/Engineers+Thumb.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bean on March 11, 2017, 01:12:46 PM
Update on my post - all 5 boards are spoken for.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DrAlx on March 15, 2017, 05:51:16 AM
Im looking to build one of these on stripboard.

The layout is on 20 row, can this be built on 19 row?
I got my vero build down to 18x18 but that involved cutting gaps between holes with a sharp blade instead of drilling out entire holes.  I also tack adjacent tracks together with solder on the bottom of the board.
Following layout includes the millennium bypass and treble boost mod.  Both can be easily omitted.
Bottom pic is view from the bottom of the board showing where to make breaks in tracks (done before anything is soldered in place) and where to blob tracks together (done after everything soldered in place). 


(http://i1368.photobucket.com/albums/ag185/DrAlx/IMG_8260_zps9ro4vdmm.jpg) (http://i1368.photobucket.com/albums/ag185/DrAlx/IMG_8260_zps9ro4vdmm.jpg)

(http://i1368.photobucket.com/albums/ag185/DrAlx/Thumb_zpstv32qyo2.png) (http://i1368.photobucket.com/albums/ag185/DrAlx/Thumb_zpstv32qyo2.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on March 15, 2017, 05:56:14 AM
[quote/]

(http://i1368.photobucket.com/albums/ag185/DrAlx/Thumb_zpstv32qyo2.png) (http://i1368.photobucket.com/albums/ag185/DrAlx/Thumb_zpstv32qyo2.png)

Dang son! That looks like what used to be on TV at 3:30 in the morning ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jfrabat on March 18, 2017, 03:50:49 PM
Update on my post - all 5 boards are spoken for.

Already got started on mine!  I am missing some resistors and diodes, which I plan to get on Monday, but what I have is already in the board!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 18, 2017, 04:56:57 PM
I now have PCBs available too. Three knob version (Attack, Ratio, Level).
http://valvewizard.co.uk/shop.html
Don't PM me here, use the email address on my website above.
(http://valvewizard.co.uk/engineersthumbpcb2.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kuzieem on May 06, 2017, 01:02:48 AM
I have  built two stripboard 2knob versions, the lm13700 and CA3080. Both have the same problem with my  bass guitar - comp knob works as distortion (in unpleasant way). Everything double-checked, been building a dozen effects successfully so far.
How can I decrease the gain of compressed signal?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 08, 2017, 08:59:51 AM
comp knob works as distortion (in unpleasant way).
This indicates there is a fault with your build. Time to post photos?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Abbott on May 09, 2017, 04:47:08 PM
I have built the compressor Merlin designed, I built it using the JMT board. I like it much more than Ross/MXR types as it doesn't colour the sound of the guitar and it isn't noisy.

My interest in the compressor is to have a "crunchy" rhythm sound and use the compressor to boost the guitar's output and provide more sustain. I'm finding that I could use more output.

Is there any thing in the circuit that could be changed that would provide more volume?

Thanks for your assistance.

Mark
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 10, 2017, 03:22:03 AM
Is there any thing in the circuit that could be changed that would provide more volume?

I *think* if you change R8 from 220R to 100R you will get a 6dB boost.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: auden100 on May 10, 2017, 05:53:50 AM
I was just fooling around this morning with the intention of finding a volume boost. I have not tried the 100R you suggested. I did have success with a 47k substitute for the 10k going from #3 on the LM13700 to the op amp output. I got just the boost I was looking for.

I have precious little electronics knowledge. Is one of these methods preferable to the other?

P.S. Thanks for all the time you put into this circuit and sharing it, Merlin.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 10, 2017, 08:43:14 AM
I did have success with a 47k substitute for the 10k going from #3 on the LM13700 to the op amp output. I got just the boost I was looking for.
That accomplishes the same thing, yes. Reducing the 220R is a lower noise, lower-offset solution than increasing the 10k, but not by much!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Abbott on May 10, 2017, 05:09:23 PM
Thanks Merlin, that should be the sort of boost I'm after. I'll give it a try and report findings.

Regards

Mark
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jfrabat on May 14, 2017, 06:40:11 PM
Hope this isn't too much of a derail: I have a version of the Thumb I made for myself which uses an LM13700 and has external pots for attack, release and threshold. Build is verified with a couple minor caveats. Anyway, I have 5 extra boards I don't need and I'm happy to just give them away. If anyone wants one lemme know.

Build doc is here: http://madbeanpedals.com/projects/Thumb/Thumb.zip

(http://madbeanpedals.com/projects/Thumb/ET_SILK.gif)

Bean,

Quick question; what do G and L stand for in the bottom of the board?  I would have thought Ground and LED+, but the L seems to be connected to the - of the LED...  Not to mention that there is LED + and - already there...  The board is all done, and I was installing everything into the case (I had to get a bit creative to fit it in, but at then end, the battery was dropped because there was no way to fit it in).  Case is painted, switch and jacks are all wired, just need to connect everything to the board...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 14, 2017, 08:13:37 PM
> what do G and L stand for

Probably go to the switch. Did you hunt MadBean's page for switch wiring info?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jfrabat on May 14, 2017, 08:29:12 PM
> what do G and L stand for

Probably go to the switch. Did you hunt MadBean's page for switch wiring info?

Good idea... I looked in the 1590G build tutorial.  It seems that the LED connects wot he LED + and -.  But that leaves the circuit open, and the L is the - of the LED, which goes to the stomp switch.  G is ground to the stomp switch.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jfrabat on May 14, 2017, 11:14:25 PM
Just wanted to report the pedal is finished and working...  Thanks, Bean!!!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on May 15, 2017, 09:48:29 PM
.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on May 16, 2017, 12:25:25 AM
.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: antonis on May 16, 2017, 05:15:07 AM
Just finished a 4 knob version (Attack, Release, Compress & Level) incorporated in a multi-effect pedal and it simply sounds fantastic in front of either a Fender Blender, a (modified) Mig Muff or a Wampler Triple Wreck..!!    :icon_biggrin:

@Merlin, you rock, man..!!!  :icon_lol: :icon_lol: :icon_lol:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Abbott on May 16, 2017, 05:55:09 AM
Antonis, thanks for the feedback on your compressor build. I experimented with the attack knob but found there was a sweet spot I liked and I'd just put a fixed resistor in, basically I wanted some delay so the attack of the note is preserved somewhat so the compressor still allows the guitar to sound natural. What is the release control like?

Regards

Mark
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: antonis on May 16, 2017, 09:06:21 AM
@ Mark: As for Relase control, I used a CCW 1M linear pot in series with a 220k resistor..
As for Attack control, I've made a "mark" on knob's travel for my own prefered spot..  :icon_wink:

 
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Abbott on May 16, 2017, 04:10:27 PM
Thanks for your reply.

How pronounced is the effect of the release control?

Regards

Mark
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: antonis on May 17, 2017, 06:33:27 AM
How pronounced is the effect of the release control?
To be honest, not much.. :icon_redface:
(at least, not as much as I expected..)

It could be replaced by a selector switch with 3 - 4 resistors ranging from 220k to 1.2M, with indermediate values..
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Mark Abbott on May 17, 2017, 07:34:48 AM
I currently have the 1M resistor as the release control. I think it hangs on a bit too long.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: antonis on May 17, 2017, 07:38:58 AM
Why don't you try a 560k, say..??
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: midwayfair on May 22, 2017, 01:00:16 PM
I did have success with a 47k substitute for the 10k going from #3 on the LM13700 to the op amp output. I got just the boost I was looking for.
That accomplishes the same thing, yes. Reducing the 220R is a lower noise, lower-offset solution than increasing the 10k, but not by much!

Huh. I would have thought the 13700 would still drive you down to unity no matter what you did in the feedback loop. Am I wrong about that? I've always sort of accepted that the max output of a sufficiently large signal in this design is 1K dividing the volume pot.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 23, 2017, 03:53:35 AM
To be honest, not much.. :icon_redface:
(at least, not as much as I expected..)
It could be replaced by a selector switch with 3 - 4 resistors ranging from 220k to 1.2M, with indermediate values..
Yeah I was a bit overgenerous with the release time. In the latest version I suggest a 100k resistor combined with a 470k or 500k pot.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 23, 2017, 03:57:34 AM
Huh. I would have thought the 13700 would still drive you down to unity no matter what you did in the feedback loop. Am I wrong about that?
If you reduce the 220R then the opamp has to produce more output signal in order to get the same signal fed back to its inverting input, compared with the stock 220R. Hence more gain. This is a feedforward compressor remember, so modding the feedback path does not alter the side chain (e.g. the current being fed into the OTA's control pin).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on May 23, 2017, 11:48:06 AM
Merlin, have you ever though about using THAT 2181 instead of LM13700 in Engineer's Thumb? I would like to try this on my own, but my knowledge is still too poor for such an adventure. :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 23, 2017, 07:29:10 PM
> though about using THAT 2181 instead of LM13700 in Engineer's Thumb?

It wouldn't be "using", it would be a complete re-design. The '3080/'13700 OTAs are linear current control; the THAT parts are log voltage control. The side-chain design would be quite different. The OTAs have a low input voltage overload, which dominates good design; the THAT parts are current input and overload is simple scaling.

No doubt Merlin could design around the THAT chips. For that matter, THAT publishes comprehensive "how to use our stuff" papers you can just use verbatim. I seem to recall they published some stuff for low voltage (instead of the +/-15V world assumed in most THAT docs). Look at THAT 4315 (http://www.thatcorp.com/4315_Low-Cost_Low-Voltage_Analog_Engine.shtml).

AH!! See  9V-Powered Effects Pedal Designs (http://www.thatcorp.com/pedals/index.html). Pedal Design Three: 4316-based Simple Limiter is one THAT chip and one dual opamp. I suspect it wants an input buffer to avoid loading a guitar. Design Four has such a thing.

The straw is that the THAT chips are harder to get and higher price than the OTAs. People balk at Small Bear's price for known-good '3080 ($5). Merlin may have swung to '13x00 because they sell under $2. The 2181 go $5-$10. Which I think is cheap, but this is a cheap crowd.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 24, 2017, 04:25:29 AM
(https://ci.memecdn.com/9991675.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: EBK on May 24, 2017, 08:00:27 AM
Then there's the issue (an inconvenience, mostly) of the QSOP footprint for in-production THAT chips.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mlp-mx6 on May 24, 2017, 11:14:27 PM
Then there's the issue (an inconvenience, mostly) of the QSOP footprint for in-production THAT chips.
Not all of them.  For example, the 4301 is still available in DIP-20 form.
http://www.mouser.com/ProductDetail/THAT/4301P20-U/?qs=sGAEpiMZZMvxTCYhU%252bW9mSHGcoR5HnTi6ZnSaFFEg3U%3d
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: mlp-mx6 on May 30, 2017, 09:36:01 AM
Huh. I would have thought the 13700 would still drive you down to unity no matter what you did in the feedback loop. Am I wrong about that?
If you reduce the 220R then the opamp has to produce more output signal in order to get the same signal fed back to its inverting input, compared with the stock 220R. Hence more gain. This is a feedforward compressor remember, so modding the feedback path does not alter the side chain (e.g. the current being fed into the OTA's control pin).
Just a quick note of confirmation.  My ET had only ever barely reached unity volume.  I changed the 220R to 100R and the available level is now MUCH higher.  Perfect. Thanks, Merlin.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on August 09, 2017, 05:24:42 AM
It's a really nice circuit and sounds great! Thanks. I made a few small mods to my build.

I paralleled up the 2 OTAs for a modest improvement in SNR. I just added a 1k resistor in series with each bias control input to make sure the two halves shared the bias current equally. I also replaced the main signal path op amp "A" with an NE5534 using a 68pF compensation cap (it needed to be this big for unconditional stability on my build). This reduces the overall output noise by about 8dB compared with the stock design.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: stan-thomas on October 02, 2017, 10:13:38 AM
I paralleled up the 2 OTAs for a modest improvement in SNR. I just added a 1k resistor in series with each bias control input to make sure the two halves shared the bias current equally. I also replaced the main signal path op amp "A" with an NE5534 using a 68pF compensation cap (it needed to be this big for unconditional stability on my build). This reduces the overall output noise by about 8dB compared with the stock design.

Lower noise? Awesome. Please could you share the schematic.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on October 02, 2017, 11:02:40 AM
Perhaps something like this? I have tried to modify schematics according to jonny.reckless notes, hope I understood him well. Take a look at this PDF:
https://drive.google.com/open?id=0B1wLPwWafEnXTkRKMl93UVZkVms
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on October 12, 2017, 08:20:20 PM
Hello.
A couple of questions are interesting.
1) Why is there such a large 10M resistor at the input, is it protection from the 3PDT cheat instead of which it is possible to install more common 1M 2M2 or for this scheme necessarily the value of 10M?
2) Why are LEDs on the input?
3) Transistor BC327, is it necessary or can it be replaced by another common PNP transistor like 2N3906 or 2N5087 / BC560?
4) The volume control has a non-standard value of 10K instead of the classic 100K
How important is the value of this potentiometer?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on October 13, 2017, 04:48:05 AM
Hello.
A couple of questions are interesting.
1) Why is there such a large 10M resistor at the input, is it protection from the 3PDT cheat instead of which it is possible to install more common 1M 2M2 or for this scheme necessarily the value of 10M?
It is the anti-pop bleed resistor. You can use 1Meg if you prefer, or 2M2 on each side of the cap if you want to maintain ~1Meg input impedance.

Quote
2) Why are LEDs on the input?
They're pre-clippers. They're needed because the circuit does not clip pleasantly by itself.
More explanation here: http://valvewizard.co.uk/engineersthumb2.html
Quote
3) Transistor BC327, is it necessary or can it be replaced by another common PNP transistor like 2N3906 or 2N5087 / BC560?
Yes any general purpose transistor should work, see the webpage.
Quote
4) The volume control has a non-standard value of 10K instead of the classic 100K
How important is the value of this potentiometer?
10k is the standard for opamp circuits (actually 5k may be more more common now that opamps have got so good). But 100k will 'work', though output impedance will be much worse of course, so personally I would never recommended a 100k output pot.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on October 13, 2017, 07:42:30 PM
> Transistor BC327

"Any PNP". The specs are nearly unimportant. I can't think of any PNP that won't work. >4V, >4mA, hFE>1, fT>0.1KHz.

You do NEED to know the pin-out. If you get the Base wrong it can't work. I suspect C and E could be swapped and 9 of 10 times it would "work", maybe less-good.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on October 13, 2017, 08:27:52 PM
merlinb

Thank you so much
I do not have all the components in my store, your explanations helped me a lot.
Regarding the volume control, I can set the output buffer to avoid the effect of the volume control on the output impedance.
The volume controls of the 100K classic in many distortion pedals, I thought it was a classic and logical denomination for the regulator, maybe it's worth it in the future to try to decrease the volume control's rating in its layouts.
Once again, thank you very much!


If I correctly understand the circuit input resistance 10M // 1M (Threshold Potentiometer) = 1M
It turns out that if the threshold setting is changed, the input resistance will change.
I'm right?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on October 13, 2017, 08:30:28 PM
> Transistor BC327

"Any PNP". The specs are nearly unimportant. I can't think of any PNP that won't work. >4V, >4mA, hFE>1, fT>0.1KHz.

You do NEED to know the pin-out. If you get the Base wrong it can't work. I suspect C and E could be swapped and 9 of 10 times it would "work", maybe less-good.


I still do not understand the principle of operation of such effects as  noise gate and compressor
So I ask such questions, I gradually study the effect behind the effect, but until noise gate and the compressor has not reached yet
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on October 14, 2017, 04:02:51 AM
The volume controls of the 100K classic in many distortion pedals,
Yeah, pedals from the 1970s!  :icon_lol:

Quote
It turns out that if the threshold setting is changed, the input resistance will change.
No the input resistance stays the same. The wiper moves up and down the track but the total resistance when looking into the top of the pot does not change.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on October 14, 2017, 09:42:09 AM
The volume controls of the 100K classic in many distortion pedals,
Yeah, pedals from the 1970s!  :icon_lol:

Quote
It turns out that if the threshold setting is changed, the input resistance will change.
No the input resistance stays the same. The wiper moves up and down the track but the total resistance when looking into the top of the pot does not change.


80s and 90s too =)
Do you recommend changing the volume controls to A10K?
I have 2 projects based on Marshall Blues Breaker and Fuzz Face / Tone Bender (the default setting is generally 500K)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on October 15, 2017, 03:03:02 AM
10k is a good value for a volume control connected to the output of an op-amp.
The Fuzz Face doesn't, AFAIK, have an op-amp at the output.
The Blues Breaker does use op-amps, but the volume control comes after the tone control, etc, so is not directly connected to the output.

Ultimately, this decision requires some understanding of impedance...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on October 15, 2017, 01:48:16 PM
Quicky question. I have none 1N4148, just some other diodes. Can I replace temporarily the original diodes 1N4148 with some of these:

DIODE         N.
Bat41         4
Bat46         2
1N914         1
1N60P         3
1N34A         1
1N270         2
1N4733 zener      1
1N4005         1
1N4007         4

Thanks! ;)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: blackieNYC on October 15, 2017, 03:16:00 PM
1N914 is close enough, and I'm sure the 400X would work.  Ge and schottky and LEDs would probably change operation a bit. Should avoid the 1N60, 1N34, the BATs, and the zener.
Looks like you really only need three for the basic circuit.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on October 15, 2017, 04:27:19 PM
Thank you. :) In case I'll do some tests with the 1N4007.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on October 15, 2017, 11:57:45 PM
Quicky question. I have none 1N4148, just some other diodes. Can I replace temporarily the original diodes 1N4148 with some of these:

DIODE         N.
Bat41         4
Bat46         2
1N914         1
1N60P         3
1N34A         1
1N270         2
1N4733 zener      1
1N4005         1
1N4007         4

Thanks! ;)


1n914 - uniquely, these diodes often figure as a replacement for 1n4148 and vice versa
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on October 16, 2017, 02:56:59 AM
Too bad, I have just one 1N914. Anyway, I already have in the cart the three 1N4148.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on October 28, 2017, 01:55:15 AM
@rankot you might not need the 100pF feedback capacitor around op amp A if you use an externally compensated op amp such as the NE5534. A 68pF compensation capacitor is pretty heavy compensation for that amplifier, and should be unconditionally stable for all gains depending on the stray capacitances and inductances in your particular build. I found I didn't need it. And yes, you just parallel up the OTAs for a 3dB improvement in noise figure. The 1k resistors are there just to make sure the current mirrors in each half of the LM13700 get approximately the same current into them.

Merlin did a great job here. It's rapidly becoming my favorite compressor. One other small mod I have done to mine is to add a J112 as a common drain (source follower) buffer on the input stage, so I could use a lower impedance 100k pot for the threshold control, which I found also improved the noise level a small amount.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on October 28, 2017, 07:14:29 AM
Merlin did a great job here. It's rapidly becoming my favorite compressor. One other small mod I have done to mine is to add a J112 as a common drain (source follower) buffer on the input stage, so I could use a lower impedance 100k pot for the threshold control, which I found also improved the noise level a small amount.

You mean something like this?

(http://i65.tinypic.com/24o527c.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on October 30, 2017, 02:50:07 AM
You don't need an input cap, or to bias the gate of a J112 to 4.5V, just connect a 1M from input to ground, and a series gate stopper of 1k to 10k into the gate. The drain goes to 9V, the source has a resistor of around 4k7 or so, and it will bias somewhere between 2 and 5 volts due to the VGSoff off the J112.

Something a bit like this. Apologies for the shitty hand drawn circuit. I'll try and sketch up something a bit better.
(https://s1.postimg.org/3pffb3hgxn/IMG_20171029_235739.jpg) (https://postimg.org/image/3pffb3hgxn/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on November 02, 2017, 12:22:47 AM
Thanks, I am building this!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on November 12, 2017, 04:58:10 AM
Maybe stupid question, but if I increase C8 (treble boost capacitor), will it decrease treble boost threshold frequency or make it bigger?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on November 12, 2017, 05:09:27 PM
^ increasing the 4n7 cap will reduce the corner frequency. If you want more gain, decrease the value of the 10k resistor in series with this cap and then re-scale the 4n7 resistor appropriately - e.g. 4k7 + 10n.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on November 13, 2017, 06:31:35 AM
Is it calculated the same as on this page?

http://www.muzique.com/schem/filter.htm
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on November 13, 2017, 07:43:04 AM
^yes, that will calculate the high-pass corner frequency.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: CC-TOP on December 23, 2017, 01:55:11 PM
https://dl.dropboxusercontent.com/u/57831278/TheEngineersThumbGTI.pdf
Are these still available? Dropbox says the file is not found :(
I have fixed the PDF link, but I can't seem to find the bitmap at the moment...

Is the pdf still available somewhere? I would like to include the LM3915 LED indication in my build :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on December 28, 2017, 02:55:47 AM
I've built Fencepost noise gate with success few days ago, and since it is also using LM13700 OTA as it's main engine, I thought that it could be nice to combine it with Engineer's Thumb, so to have a single Gate/Compressor pedal. This is what I have in mind, but I would be happy to have some suggestions from experienced DIYers. I've ommited switches (treble boost and gate/expander) from schematic, because I don't think there would be enough place for them on a 1590B pedal, and I also added compression indicator LED as proposed here by PRR, although I never made it work good enough.

(http://i67.tinypic.com/6poi05.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: thehallofshields on January 04, 2018, 02:19:21 PM
Would it be possible to add a switch for Feedback Compression? You know, to have a mode to get the Orange-Squeeze pumping effect?  :icon_lol:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on January 04, 2018, 06:47:33 PM
if there are settings on existing pots that create the effect you desire, you can always hard wire them to a 3PDT switch for a quick switched dial-in.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 05, 2018, 04:34:45 AM
Would it be possible to add a switch for Feedback Compression? You know, to have a mode to get the Orange-Squeeze pumping effect?  :icon_lol:
In principle yes, although I haven't tried it.
(https://s17.postimg.org/sy9st422z/wes.jpg) (https://postimg.org/image/sy9st422z/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on January 05, 2018, 05:34:15 AM
Another take on combining the best Engineer's Thumb Compressor with Fencepost Noise Gate. I think this is better than the first schematics:

(http://i67.tinypic.com/2moeek8.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kristopher612 on February 18, 2018, 03:36:20 PM
Hey everyone, i just finished this on Merlin's original 2 knob PCB, and i'd just like to check my voltages against a known working ET.  i haven't put in a bypass switch, so the issue is i'm not easily able to tell that  it's working.  these voltages were taken with a 1 spot PS.
Modifications: i omitted the millennium bypass portion.  i also put in a 100k attack control and a 100k resistor+500k release control.  i'm pretty sure it works, but i'd just like to verify since i haven't wired a switch up yet. thanks for any help you can give!

Q1 (2N3906)
1 - 4.33
2 - 3.7
3 - 1.3

U1
1 - 4.67
2 - 4.66
3 - 4.24
4 - 0
5 - 4.24
6 - 4.67
7 - 4.92
8 - 9.39

U2
1 - 3.8
2 - 4.41
3 - 4.2
4 - 0
5 - 4.67
6 - 4.67
7 - 4.67
8 - 9.39

U3
1 - 1.29
2 - 0
3 - 4.68
4 - 4.68
5 - 4.68
6 - 0
7 - 0
8 - 0.008
9 - 0
10 - 0
11 - 9.39
12 - 0
13 - 0
14 - 0
15 - 0
16 - 0


Title: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kristopher612 on February 18, 2018, 07:31:24 PM
I have a quick update on my build. I was playing through it, and it started making a rustling sound, turns out I had some cold joints around the socket for the 13700, so I reflowed the solder. Now I’ve got definite squish once I raise the compression ratio, and the attack and release controls are doing their jobs accordingly. I may get a few smaller log taper pots for the attack control and see if I get more usable range out of it.
All that said, thank you Merlin for a great project. I haven’t owned a compressor in years and this was a fantastic way to fill that hole.


Sent from my iPhone using Tapatalk
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: vefaerdem on February 19, 2018, 01:56:42 AM
Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on February 19, 2018, 04:51:03 AM
Here they are:

(http://i66.tinypic.com/2v2ejdg.jpg)

(http://i66.tinypic.com/jpzslc.jpg)

I have built this version with LED indicator and it didn't behave as expected.

(http://i67.tinypic.com/6z1ssm.jpg)

I didn't try this one with meter, maybe it works fine?

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: 287m on February 19, 2018, 04:55:07 AM
Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

this (https://drive.google.com/open?id=1zhaCwEwlZOl4_GyBCnXsODtJSfgX3uXZ)?
and welcome
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: vefaerdem on February 19, 2018, 05:47:19 AM
Any chance to have schematic for 5 knobs version with noise reduction meter leds again? It seems all the docs shared on this forum are outdated and unavailable.

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

this (https://drive.google.com/open?id=1zhaCwEwlZOl4_GyBCnXsODtJSfgX3uXZ)?
and welcome
Oh, a pcb layout in a vector file format, that's awesome :)) thank you mate!

GM 5 Plus cihazımdan Tapatalk kullanılarak gönderildi

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: BetterOffShred on February 20, 2018, 05:23:53 PM
It's becoming abundantly clear to me that I need to take the plunge and start etching some PCB's.   Ring Stinger, This, That Jok3rX high gain thingy..  A lot of cool PCB's to etch..
 :icon_eek:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on March 17, 2018, 09:05:16 PM
   In the spirit of Jonny.Reckless' mods (FET, NE5534 & VCA "paralleling"), any other low-noise opamps able to be used/substituted for the TL072 in the audio path, for further noise reduction ?

   There's a couple I can get real cheap at a near-by surplus shop (they even have old SSM2017s, a buck-a-piece !) :


-OP27                                    noise : 3 nV/"Hz
-I have some LM4562 (dual)    noise : 2.7 nV/"Hz
-I might order some AD797      noise : 0.9 nV/"Hz (used in the Forrest Green comp, I reckon... oh : $18 !)
-LT1115, maybe ?                    noise : 0.9 nV/"Hz as well (but way cheaper at $6)
-any other ? (money's no object : the way I see it, even a $20 chip would be worth it, in my Quest for the Holy-Grail Noiseless, Endless, Extreme Compression DIY pedal ! )


TIA !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on March 18, 2018, 12:50:47 AM
Welcome.

There's always hiss.

We say the limiter "turns down the loud parts", but in fact we always use it to turn up the soft parts.

Including the hiss.

The guitar hisses.

Hiss is not just voltage hiss. At guitar impedance, current noise also matters significantly.

The TL072 is very nearly as low-hiss as a guitar's self-hiss impedance. You can do a little better. Not a lot.

You will generally be looking for FET input. Bipolar input tends to be too much hiss current. If not, then the input is so starved the voltage hiss comes up. I know there is a "better FET input" chip, but don't recall its name.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on March 18, 2018, 01:23:25 AM
Thanks PRR !


   Yeah, I know  :-\ : chasing after noise is sort of a  pointless endeavour in the world of RAWK guitar ; but, I love the Engineer's Thumb sooooo much, 'though : can't blame a guy for trying.

   I'd die for a real lush, chorused & heavily compressed chord, to slooowlyyy fade into... pure silence ! (there's a volume knob for that, I know...  :icon_rolleyes:)

   And : I'm also looking into DIY very-low-impedance pick-up (I built a prototype flat-mount, 1mm thin, stealth over-bridge-pu/under-pu-cover, 35 Ohm hex pu, needing preamps & nearly-silent, heavy compression for well...  Belew-esque experimental extravaganza ! Looking at CYC-FI schematics for the moment...)


Anyways, whenever you recall the opamp number : i'm all ears !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on March 18, 2018, 09:11:08 PM
Paul,

   Were you thinking of AD743/AD745 by any chance ? Lowest noise BiFET inputs opamp I can find, so far : 2.9nV/rootHz...

   I was doing some reading : how 'bout "paralleling" 4 opamps, for 1/2 the noise ? (Or 8 ! Go big or go home, I say ! ;D ) I'd go with 4 parallel LT1115 (o.9nV/rootHz-$6 a-piece) using Jonny.Reckless's 2N5457 "buffer" in front, for a "theoretical" noise contribution of 0.45nV/rootHz ? Does this make any sense ?

   It'd be worth the $24 to me, fer sheeeur... if : it works, that is...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on March 18, 2018, 11:23:37 PM
The resistance of a gitar in the hiss band is near 20K.

In a 20KHz bandwidth, that is about 2uV.

2.9nV/rootHz over 20KHz is about 0.4uV.

Try them all. You can do a bit better than TL072. I submit you can't do a "lot" better, the guitar self-hiss dominates.

Turn down the amp, strum harder.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on March 19, 2018, 06:26:17 AM
Turn down the amp, strum harder.

And there folks... is my new sig line.  :icon_lol:

Thanks Paul!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on March 19, 2018, 01:29:22 PM
are you building a guitar pedal for stage? or a rack unit for the studio? if it's for stage, forget about hi-fi hiss concerns, especially if you play with a drummer who uses cymbals. if you have a house gig at Orchestra Hall and they're micing you with a pair of $10,000 Schepps or something, ok, then bring your rack gear, leave the pedals at home. If you're building recording gear, just build an SSL clone or something. gonna find a low noise OTA?

Quote
any other low-noise opamps able to be used/substituted for the TL072 in the audio path, for further noise reduction ?
that matters for mic pres, for instance, basically doesn't matter for guitar stuff, like what Paul said. if you ever get a chance to look in a top shelf console, check out the op amps, you might be shocked :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: brett on March 21, 2018, 02:32:23 AM
For less noise.... lower that 10M pull-down resistor at the input to 220k. You'll lose those 100kHz highs that bats and dolphins love but I doubt you'll miss them.
(and yes, I do know that the input impedance is already much less than 10M)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on March 21, 2018, 04:37:39 AM
For less noise.... lower that 10M pull-down resistor at the input to 220k.
No no no, that will increase noise i.e. worsen the signal to noise ratio!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on April 27, 2018, 05:29:22 PM
I really love this compressor. I have made some modifications:

JFET input buffer (improved transparency with single coil pickups)
Reduced self noise (parallel up the 2 halves of the LM13700, replace TL072 with NE5534 low noise audio amplifier, reduce the base impedance of the LTP in the LM13700) in total by about 10dB w.r.t. the original design
Added a simple noise gate
(https://s31.postimg.cc/ryed2wix3/thumb.png) (https://postimg.cc/image/ryed2wix3/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Beo on April 27, 2018, 10:15:53 PM
Jonny, does the noise gate work well? Consistent for single/dual coil, clean and distortion? Is it set and forget (maybe install as trimmers)?

Thanks!
Travis
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on April 28, 2018, 02:00:56 AM
I have this as the first thing in my chain. I imagine it would be difficult to gate the noise once it's already been compressed or distorted. It works well for me. It's a soft gate in that it progressively applies up to 30dB of gain reduction when the signal is below the threshold. It never hard mutes. I generally don't need a gate with humbuckers. You could easily scale the range if you need to by adjusting the value of R18: smaller value makes the gate open at a lower threshold, or you could replace the pots for fixed settings if you like. If you want to make the gate switchable just install a toggle switch in series with the collector of TR3.

I use these to wire up the sockets, switch, power supply and LED:
https://www.taydaelectronics.com/pcb/diy-guitar-effects/3pdt-footswitch-diy-pcb.html (https://www.taydaelectronics.com/pcb/diy-guitar-effects/3pdt-footswitch-diy-pcb.html)

I'm planning to do a PCB when I get time.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on April 28, 2018, 05:57:05 AM
I'll do a PCB if this is verified schematics. I tried to combine Fencepost noise gate with Engineer's Thumb, but didn't have enough time to complete it, and that one was really complicated. This one looks better!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: BetterOffShred on April 28, 2018, 10:46:11 AM
I'll buy one :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on April 28, 2018, 12:10:56 PM
Few questions for jonny.reckless:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on April 28, 2018, 02:33:30 PM
I found I didn't need the threshold pot since the sustain pot has pretty much the same action. All the decoupling caps go to ground intentionally. When I do the PCB, the whole of the top copper layer will be ground plane which will keep noise to a minimum. I usually do analog audio on 2 layer boards with one layer dedicated to ground. It works really effectively for guitar stuff.

I tried to keep the gate simple. It just dumps current into the OTA control pin and therefore sets maximum gain reduction. Of course the OTA noise is then at its maximum but with 2 of them in parallel and 22 ohm base impedance it's pretty quiet.

It's not a hard mute. You may also add a cap (100n or so) across R13 to make the gate open slightly less jumpy if you prefer. I like a noise gate to open instantly so it doesn't cut off the first half cycle of the note. This is especially important with drop tunings.

I've not considered a blend pot although with the JFET buffer on the input it would be fairly easy to add one if you wanted to. I find parallel compression doesn't sound great on anything except drums.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on April 29, 2018, 10:02:22 PM
I have done a quick place and trial route. This should fit into a 1590B enclosure.  Still have a bit of work to do...


(https://s31.postimg.cc/7hmt6r0g7/Capture.png) (https://postimg.cc/image/7hmt6r0g7/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on May 01, 2018, 05:52:10 AM
Is it necessary to use TL071 for Vref generation, why not something like this:
(https://s26.postimg.cc/5qw6oaddl/Vref.jpg)
Smaller footprint.

If it is necessary to use op amp for Vref, why not using NE5532 instead of NE5534, so one half of it can be used for Vref? One IC less.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 01, 2018, 10:43:07 AM
If it is necessary to use op amp for Vref, why not using NE5532 instead of NE5534, so one half of it can be used for Vref? One IC less.
Probably trying to keep current consumption down. TL071 needs <2mA, whereas NE5532 takes about 4mA per section.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jamierichards1234 on May 02, 2018, 08:52:44 AM
Hi, Firstly I want to say thanks Merlin for sharing this excellent design. I've built mine and it's up and running, but I'm wondering if anyone has any ideas how to modify it to further reduce the release time?

I've swapped out the 470k resistor for a 500k pot which I currently have in series with a 47k resistor to stop me going too far (47k seems to be as low as I can get away with before everything goes mental). It's getting me close to where I'd like to be but it would be really nice to have the option of even shorter release times. Also I'd rather not be running it right on the edge of instability if possible! 

Anyone got any suggestions of how I might be able to do this? I don't mind losing the option of longer release times to get there..


(FYI the reason I'm after shorter release is that I'm using an external sidechain for 'ducking' to a kick drum but the signal doesn't quite come back up as fast as I'd like)

Many thanks,

Jamie
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 02, 2018, 11:02:13 AM
t it would be really nice to have the option of even shorter release times.
Use smaller smoothing caps in the side chain, e.g. swap the 1u caps for 470nF. This will halve the attack/release times. You get less smooth control voltage though, obviously, which is the price you pay for short release.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on May 02, 2018, 03:31:29 PM
t it would be really nice to have the option of even shorter release times.
Use smaller smoothing caps in the side chain, e.g. swap the 1u caps for 470nF. This will halve the attack/release times. You get less smooth control voltage though, obviously, which is the price you pay for short release.

Just a spitballin' question; If going with smaller caps, would the type of composition play a roll in helping smooth the control voltage? Example, using polystyrene rather than polyester or metal film.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 02, 2018, 05:05:02 PM
would the type of composition play a roll in helping smooth the control voltage? Example, using polystyrene rather than polyester or metal film.
No way. It's not smooth as in "smooth tone, bro!" we're talking about here, it's your grandpa's good old fashioned rectified ripple, and it doesn't care what your caps are made of!  ;)
(https://upload.wikimedia.org/wikipedia/en/thumb/2/29/Smoothed_ripple_gray_background.svg/868px-Smoothed_ripple_gray_background.svg.png)
(Actually it's only a half-wave rectifier in the side chain, but you get the idea)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on May 02, 2018, 10:22:45 PM
Alrighty-o then. Never any harm in asking. Thanks Merlin. :icon_biggrin:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on May 07, 2018, 11:52:59 PM
I got the PCBs for the "Engineer's Thumb redux" this evening. I will try and get one built up over the weekend and post some audio.

(https://s31.postimg.cc/aguq80213/IMG_20180507_201856409.jpg) (https://postimg.cc/image/aguq80213/)

(https://s31.postimg.cc/yxcw2hahj/IMG_20180507_201905733.jpg) (https://postimg.cc/image/yxcw2hahj/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on May 08, 2018, 12:17:37 AM
Is it necessary to use TL071 for Vref generation, why not something like this:
(https://s26.postimg.cc/5qw6oaddl/Vref.jpg)
Smaller footprint.

If it is necessary to use op amp for Vref, why not using NE5532 instead of NE5534, so one half of it can be used for Vref? One IC less.

I generally find zeners are very noisy especially around 5V. Also without feedback the output impedance of the emitter follower will be relatively high (and dependent on current). The NPN can only source current and not sink it. The op amp based VBIAS is pretty simple and cheap and works well.  For a general purpose regulator I really like the LM317 series, they are quiet and have excellent line and load regulation. But again are unipolar only.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on May 08, 2018, 12:25:23 AM
If it is necessary to use op amp for Vref, why not using NE5532 instead of NE5534, so one half of it can be used for Vref? One IC less.
Probably trying to keep current consumption down. TL071 needs <2mA, whereas NE5532 takes about 4mA per section.

I used the external compensation pins of the NE5534 to guarantee stability of the op amp under heavy dynamic gain reduction. I found this approach worked better than the feedback pole/zero of the original design. But that might have been an artifact of my vero prototype. The NE5534 is cheap, widely available in DIP, has very low noise, low output impedance (i.e. strong drive capability), low distortion and is externally compensated for noise gains less than 3. It's one of my favorite audio op amps.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on May 08, 2018, 04:57:59 AM
What about gate LED indicator?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: iiimonfire on May 08, 2018, 07:32:23 AM
Hey all! I've been looking for a new low-noise compressor for bass, and have been reading up on this. I breadboarded it over the weekend according to Merlin's schem: http://www.valvewizard.co.uk/engineersthumbschem2.jpg (http://www.valvewizard.co.uk/engineersthumbschem2.jpg) with all of the mods to make it a 5-knob pedal (volume, threshold, ratio, attack, release).

One thing I am noticing is that turning the ratio knob CW will dramatically amplify the signal, so that it distorts heavily way before ratio is at ~50%. That basically renders more than half of the pot range pretty much useless.

I've tried switching out the LM13700 with one that was working in a Keeley compressor I made - so I'm guessing that's not the culprit. I've gone over the schem and the vero layout I created as well, and I am pretty sure they are correct. FWIW, I'm using a TL074CN instead of two TL072's which I see a lot of other layouts (e.g., Tagboard, Sabrotone) using.

Any ideas what could be causing this massive distortion?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: GGBB on May 08, 2018, 07:46:14 PM
The NE5534 is cheap, widely available in DIP, has very low noise, low output impedance (i.e. strong drive capability), low distortion and is externally compensated for noise gains less than 3. It's one of my favorite audio op amps.

Do you ever have problems or see reduced performance (noise or whatever) with it running off of 9V? Recommended minimum supply for it is 10V. I'd assume the first spec to suffer at lower voltages would be noise, but I really don't know.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on May 09, 2018, 02:15:12 AM
I've not noticed a problem at 9V but I've never put it on the AP to measure it at that voltage. It definitely gets a bit grainy at 5V. It consumes about 4mA at 9V input so I guess the internal bias circuits are OK.

Beware cheap NE5534s off eBay. I've been caught out with some absolute crap. I buy mine from mouser or digikey now.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on May 09, 2018, 02:22:01 AM
What about gate LED indicator?

It's pretty straightforward to rig one up but I just use my ears  :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 01, 2018, 07:23:28 PM
I finally got the PCB for this debugged and working.

Here is the schematic:
(https://s33.postimg.cc/89gt8ffvf/Capture.png) (https://postimg.cc/image/89gt8ffvf/)

Photo of the PCB:
(https://s33.postimg.cc/r32m4wj2z/IMG_20180513_164837538.jpg) (https://postimg.cc/image/r32m4wj2z/)
(https://s33.postimg.cc/ridvy82iz/image.jpg) (https://postimg.cc/image/ridvy82iz/)

Video of the unit in operation:


Many thanks to Merlin for sharing his fantastic design.

Let me know if you would like a PCB. I can send you one for $10 plus postage. My email is jonny@recklesstechnology.com
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on June 02, 2018, 12:37:56 AM
Let me be the first to warmly congratulate YOU ! Am-A-Zing job on the integration of the gate !

You mention adding a bit of hysteresis to the gate, preventing chatter (during note fade-out, I gather ?)... does the current schematic reflect this ?


Wow... & love the playing ! (btw, great songs on YT, too !)


P.S. : could a 2SK117GR sub for the J112 with minimal tweaking, you reckon ?

Double P.S. : separate Attack & release (Decay ?) pots. would be GREAT for SlowGear-type volume swell effects ! Hopefully possible ?
                       (please-please-please-please-please-please ?)
                       That'd make it the ULTIMATE pedal for me !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 02, 2018, 04:07:01 AM
Let me be the first to warmly congratulate YOU ! Am-A-Zing job on the integration of the gate !

You mention adding a bit of hysteresis to the gate, preventing chatter (during note fade-out, I gather ?)... does the current schematic reflect this ?
Current schematic is what I am playing in the video.


Wow... & love the playing ! (btw, great songs on YT, too !)
Thanks!

P.S. : could a 2SK117GR sub for the J112 with minimal tweaking, you reckon ?

Double P.S. : separate Attack & release (Decay ?) pots. would be GREAT for SlowGear-type volume swell effects ! Hopefully possible ?
                       (please-please-please-please-please-please ?)
                       That'd make it the ULTIMATE pedal for me !

You could replace each of the attack / decay resistors with a 1 megohm log pot.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on June 02, 2018, 04:28:15 AM
Wonderful updating of this compressor! Though I'm not a great fan of compressor effects, I'm building this ultra settable one using the Sabrotone layout (probably including the two missing LEDs that it doesn't have).
http://www.sabrotone.com/?p=2901
Actually, I stopped for missing parts.

Your circuit gets the schematic more complex, but I'm wondering if I could include your noise gate on a daughter board, I'm still trying to follow the schematics (original and new), I'd need more time.

Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on June 02, 2018, 01:09:49 PM
HEY, jonny. !



"You could replace each of the Attack / Decay resistors with a 1 megohm log pot"

-The Decay must be R20 (release ?) in your schem., I'm guessing ?
-Which would be the Attack resistor ? (R16 and/or R15, probably ?) (just after the gate rectifier ?)



Thanks in advance !


P.S. : and please, keep us updated on the hysteresis "tweaks"

...this is getting real exciting !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 02, 2018, 01:32:39 PM
HEY, jonny. !



"You could replace each of the Attack / Decay resistors with a 1 megohm log pot"

-The Decay must be R20 (release ?) in your schem., I'm guessing ?
-Which would be the Attack resistor ? (R16 and/or R15, probably ?) (just after the gate rectifier ?)



Thanks in advance !


P.S. : and please, keep us updated on the hysteresis "tweaks"

...this is getting real exciting !

The compressor attack and release are RV4 and R23 respectively.
Gate release is R20.

Gate attack with this design would be tricky. You'd probably need a dual gang pot and replace R15 and R16. I'd suggest trying maybe 1M dual log pot. I haven't tried this.

When I get round to doing the next iteration of the gate design, I'll add hysteresis to the threshold and make it so you can set attack and release of the gate with a single pot. This is probably going to make the PCB bigger so it will no longer fit into a 1590B enclosure. I'd prefer to keep it all through hole to make hand assembly easy.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on June 02, 2018, 01:53:13 PM
Yes , of course : Gate Attack is what I meant...



I get your point about "...attack... would be tricky." : I figure the Gate capacitors (C13 & C11 ?) need to be discharged, for a quick, new Attack to "register". I'll try different schemes, play around with it.

WRT size : I place components "standing" & use tiny-mini pots, so I can get most all circuits quite "miniaturized", so absolutely NO worries for me...



Thanks-a-million, jonny. for the ongoing R&D : Merlin's ET is such a great platform !

I'll be standing by...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 04, 2018, 03:36:51 AM
I think I have a design for a more flexible noise gate with hysteresis and variable attack and decay time. This becomes an 8 knob compressor gate (threshold, ratio, attack, release, gate threshold, gate attack, gate release, volume) which is starting to get out of hand :)

I have also added an LED which illuminates when the gate is providing gain reduction.

I'll post back here once I have it fully debugged. Give me a couple of weeks.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on June 04, 2018, 04:26:15 AM
Why not using Fencepost noise gate design (as I have already proposed here), it uses another half of LM13700 and one more op amp?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: GGBB on June 04, 2018, 08:06:26 AM
Is there any particular advantage to building the gate into the compressor, instead of having a separate gate pedal in front of the compressor?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on June 04, 2018, 09:07:53 AM
Yes, smaller footprint. Especially if they use the same IC.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: GGBB on June 04, 2018, 06:42:49 PM
Yes, smaller footprint. Especially if they use the same IC.

Right - so what I meant was technical advantage - something other than the obvious.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 05, 2018, 06:21:24 PM
Since you already have a VCA inside the compressor, it makes more sense to build a compressor / gate with a single VCA rather than having 2, with twice the noise, distortion, component cost etc. Plus it's probably going to take up less room on your pedal board.

Separate units might not play nicely together depending on settings.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 05, 2018, 06:27:07 PM
Why not using Fencepost noise gate design (as I have already proposed here), it uses another half of LM13700 and one more op amp?

Because I can achieve much better noise performance, and greater flexibility, with fewer components.

Merlin's engineer's thumb is a really excellent, economical, simple, high performing design. It's actually quite inspiring how well it works for the circuit simplicity. I really like this philosophy, and try to follow the same principles when doing my own designs and amendments.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: GGBB on June 05, 2018, 06:59:01 PM
Since you already have a VCA inside the compressor, it makes more sense to build a compressor / gate with a single VCA rather than having 2, with twice the noise, distortion, component cost etc. Plus it's probably going to take up less room on your pedal board.

Separate units might not play nicely together depending on settings.

Thanks, and please excuse my ignorance of the circuit. I've tried comparing the original schematic with the new one that includes the gate, but they look so different that I'm not really making much sense of it yet.

Separate pedal obviousness aside, the "same VCA" bit puzzles me. Is the gate leveraging the VCA used by the compressor - and I mean the same VCA, not the other VCA in the same chip. If it's just using the second unused VCA in the LM13700, then isn't that really two VCAs? And therefore how is two VCAs in one pedal any different noise and distortion wise than two VCAs in separate pedals? I'm really interested in differences that are actually going to matter on the pedalboard playing live, not hifi/studio level differences.

Also - "might not play together nicely" - does the built-in gate prevent that merely because you can't adjust the settings whereas a separate gate could be set up poorly to work with a compressor? In other words, I think you are talking about the obvious, but I'm not sure because of the way you phrased it.

Thanks.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: effexfreek on June 06, 2018, 12:00:06 AM
Hey, jonny. !



   A coupla' quick questions regarding your updated ET schem. :


(scratch this one  :icon_redface: : samhay below noticed you switched to an inverting configuration ! So you could attenuate, as well as compress ?)
A) Merlin's ET has a 10k between OTA out & audio-path opamp's negative input. Your 10k (R6) is in series with RV2 sustain (ratio) pot... Design tweak ? Schem. error ?

B) You omit the 220R between OTA's inputs... better S/N ratio ?

C) You have a dual/parallel network of 10k/1uF & 10k/10n between Input FET & IC1... real curious about that.



Thanks in advance !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 06, 2018, 04:52:12 AM
Here is the schematic:
(https://s33.postimg.cc/89gt8ffvf/Capture.png) (https://postimg.cc/image/89gt8ffvf/)

Cool. You're using IC1 in an inverting configuration, which means you can, at least theoretically, squish below unity gain. This is quite different to the ET.
If you feed it a hot signal, do you get unity gain out of it? If not, perhaps a make-up gain stage on the end would be helpful - could use an NE5532 to do both stages.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 09, 2018, 03:22:03 AM
That's a great idea, thanks. I will add makeup gain. For this I'll have to switch from a NE5534 to an NE5532 or maybe even LM833 for the main audio signal path op amp.

The switch to inverting was motivated by the desire to have the gate attenuate the signal by at least 20dB. The original non-inverting design does not allow for gains less than unity. I also wanted to put a JFET front end on the unit, as I have found that something like a J112 input stage generally sounds sweeter and more articulated (more high frequencies, better transients) than the JFET of a TL072 input pin, especially with single coil pickups. I don't know why this is, but if you A/B it, you can clearly hear a difference.

It's still a forward compressor with a single VCA. I parallel up the 2 halves of the LM13700 for a 3dB improvement in noise figure. The gate sets the gain reduction to maximum.

I am working on the next generation of this idea, with full control and 8 knobs: threshold, attack, release, gate threshold, gate attack, gate release, ratio and volume.

R3, R4, C2, C5 form an emphasis filter, same idea as in the original. Roughly 6dB boost at HF, first order. I moved the corner frequency down a bit. This was done purely for personal taste, and was tweaked until it sounded right on my Squier tele. C5 = 22n also sounds nice, as does 4n7.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 09, 2018, 09:48:12 PM
> The original non-inverting design does not allow for gains less than unity.

I have not looked at the design in a while.

But the OTA can have gain. So the op-amp loop can be driven below unity gain.

I think.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 11, 2018, 03:56:04 PM
> The original non-inverting design does not allow for gains less than unity.
But the OTA can have gain. So the op-amp loop can be driven below unity gain.
I think.

Yes, you are right.  I was neglecting the fact that the OTA could have a transconductance higher than the loop gain, and thus allow for overall gain less than unity. Thanks for the correction.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 11, 2018, 04:17:50 PM
I did quite a bit of work on this over the weekend. I fixed the noise gate, added hysteresis to the threshold, and generally cleaned up the performance. I also added a negative voltage converter and made the unit split power supply, which simplified things a bit. It's getting further away from the original engineer's thumb but I like the flexibility.

I'll post more when I have chance to make some recordings. This is where I have gotten to with the schematic. It's hacked together on the bench at this stage, so quite noisy, but I'll fix that with a PCB. The LMC6482 should actually be TL072 - they can't handle 17V supply.

(https://s33.postimg.cc/5ogfmd54r/Capture.png) (https://postimg.cc/image/5ogfmd54r/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 11, 2018, 04:40:47 PM
> The original non-inverting design does not allow for gains less than unity.

I have not looked at the design in a while.

But the OTA can have gain. So the op-amp loop can be driven below unity gain.

I think.

Good point. I have some recollection this won't be the case in feed back designs, but as the ET is feed forward it is possible, although I suspect you would need a hot signal and the ratio set quite low.
Perhaps someone with an ET can confirm?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 11, 2018, 10:47:35 PM
> some recollection this won't be the case in feed back designs

We all know that the Non-Inverting operational amplifier connection only goes down to unity gain.

Why? Because we use a resistor divider to set loss which is the inverse of the gain we want. But resistors alone can't make "loss less than unity" (i.e. gain). So the minimum gain is unity.

Putting gain in the feedback divider is really strange. Amplifiers are inconsistent, resistors are consistent. Who would do that? In fact it does get done frequently enough, even if not in stomp-land.

For gain of 10, we use 10:1 resistor divider. This could just as well be some (lame) "amplifier" with "gain" of 10:1 (a loss).

For gain of 1, we use 1:1 resistor divider (a strap). (Except my sim objects "floating pin" so I threw it a negligible bone.) This could just as well be some (lame) "amplifier" with "gain" of 10:1 (a loss).

For gain of 1, we use 1:10 resistor divider. Ah, that won't happen with positive resistances. β can not be greater than 1. But it could be an amplifier with gain of 1:10. Now the non-inverting connection gives gain of 0.1.

See below.

That's just DC/Audio gain. You also seem blocked on how this would work in a dynamic limiter. But any overall gain/loss can be managed by inserting gain/loss in the right places. Yes, Blesser's paper shows that as you go to extremes, feedforward and feedback have different problems. We rarely hammer on audio so hard that this is insurmountable.

(https://s33.postimg.cc/ln3e0yf97/Below_Unity-opamp.gif) (https://postimg.cc/image/ln3e0yf97/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 12, 2018, 01:50:12 AM
I'm doing a PCB layout now. It's quite a challenge fitting it all on a 100mm x 70mm PCB. I think I've got something, it just needs a little polish.
(https://s33.postimg.cc/5ewcj6ayj/Capture.png) (https://postimg.cc/image/5ewcj6ayj/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rockhorst on June 12, 2018, 05:40:23 AM
Hats of to all of you, esp. Jonny, for all the great work in this thread. I read through all 27 pages yesterday, it underlines what a great community this is (I should visit it more often).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 12, 2018, 07:09:37 AM
>That's just DC/Audio gain. You also seem blocked on how this would work in a dynamic limiter...

Thanks Paul. I seem to have mis-remembered something regarding the limits of feedback automatic gain control. Will have to put out the reading material again.
Simulation says that the stock ET can do a gain of < 1 when the signal input is hot enough (~ 1V peak with moderate-high ratio settings). Conversion to a feedback  topology can give similar behaviour.

Happy to stand corrected.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 08:22:59 AM
Maybe a dumb request, but since I've found some contradictions on the net, here goes...

Would it be possible to indicate the lug 1 for the pots on the schematic? I could never get my head past volume controls where that's concerned. Just seems that the conventions for this are all over the map.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on June 12, 2018, 08:46:38 AM
I usually put numbers on pot lugs, or CW/W/CCW.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 09:24:12 AM
I usually put numbers on pot lugs, or CW/W/CCW.

I usually just indicate "1" on my schematics. KISS principal. Like I said, volume or gain aren't a problem, I've gotten my head around those, but sometimes tone or other functions throw me completely off. I can never figure out "are they bridging 1&2, or 2&3?". "Are all the lug 1's on the left? On the bottom? On top?" Aghhhh!  :icon_cry:

And then, generally without failure, I build it only to realize that no.... I guessed wrong. :icon_mad:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 12, 2018, 10:48:11 AM
I usually just indicate "1" on my schematics. KISS principal.
But '1' doesn't mean anything. I have no idea which pin '1' is on a pot; it's not standardised (I think only ICs have a standard pin numbering pattern). Depending on who you buy your pots from, their datasheet could label any of the pins '1'. The footprint in you PCB design program could have still different numbering!
But CW/CCW is completely unambiguous.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 11:08:30 AM
I usually just indicate "1" on my schematics. KISS principal.
But '1' doesn't mean anything. I have no idea which pin '1' is on a pot; it's not standardised (I think only ICs have a standard pin numbering pattern). Depending on who you buy your pots from, their datasheet could label any of the pins '1'. The footprint in you PCB design program could have still different numbering!
But CW/CCW is completely unambiguous.

(http://3.bp.blogspot.com/-puTATV5EVeU/T5_xKwWeRWI/AAAAAAAABD4/KyYpp4vWdLg/s400/POT_LUG_NUMBERING.gif)

(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS6DeIvfnAyqXd9hqcmybxJ_KtqBeN3zrLjRcw6UxPW5b7Q0tPE)

(http://www.synthrotek.com/wp-content/uploads/2010/05/acp_pot_id.jpg)

(http://www.tdpri.com/attachments/potentiometers-front-back-png.193158/)

Or, the square pad on a PCB...

(http://i276.photobucket.com/albums/kk6/dcountry13/LUGS.jpg)

Not meaning to be a shmuck or anything... but in the general scheme of things (without getting into the "how many angels on a head of a pin" bullshit), pretty damn unambiguous to me. :icon_wink:

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Govmnt_Lacky on June 12, 2018, 11:11:17 AM
Not meaning to be a shmuck or anything... but in the general scheme of things (without getting into the "how many angels on a head of a pin" bullshit), pretty damn unambiguous to me.

Agreed! For as long as I have been building or dealing with potentiometers, the CCW-most lug has always been Lug 1.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 12, 2018, 11:16:14 AM
Not meaning to be a shmuck or anything... but in the general scheme of things pretty damn unambiguous to me. :icon_wink:
How about now?
(https://s33.postimg.cc/z950wds8b/wes.jpg) (https://postimg.cc/image/z950wds8b/)

By using CW/CCW you don't have to look anything up on google, you can always figure it out with the part in hand.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 11:19:32 AM
Not meaning to be a shmuck or anything... but in the general scheme of things pretty damn unambiguous to me. :icon_wink:
How about now?
(https://s33.postimg.cc/z950wds8b/wes.jpg) (https://postimg.cc/image/z950wds8b/)

Dude... really? Tell you what. When a DIY project gets to that point, we can settle that dust then and there. In the meantime, try keeping with the program. The subject today is apples. Not oranges.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 12, 2018, 11:20:09 AM
Dude... really?
Dude you've never used a trimpot? Or a Bourns pot? All pots are apples.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 12, 2018, 11:37:36 AM
While I wouldn't have to think too hard about what lug 1 of a pot looks like (and I tend to use that notation on schematics) there is a further fly in the ointment:

(https://media.rs-online.com/t_large/F0168336-01.jpg)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 11:48:04 AM
You know... I thought I was asking a fairly simple, maybe even mundane question. Generally, I've always been a true believer in the "there are no stupid questions" mantra, and as such, try to be true to that when I'm feeling competent enough to answer someones question.

In this case, not only does it seem that I'm going home without an answer to my question, but with Merlin's magic wand shoved up my a$$ as a parting gift.

If anyone wishes to illuminate me insofar as my question is concerned, I would be greatly appreciative. I can even do the "CW or CCW" thing. Just please don't bore me with the semantics of which lug is "LUG 1" on a 15 lug multi wafer pot.

(https://i.pinimg.com/originals/42/f3/c2/42f3c297041f68df59c1a3643da43f85.jpg)

While I wouldn't have to think too hard about what lug 1 of a pot looks like (and I tend to use that notation on schematics) there is a further fly in the ointment:

(https://media.rs-online.com/t_large/F0168336-01.jpg)

How about 1A, 2A, 3A and 1B, 2B, 3B? Sort of like what's used on rotary switches? (Now I duck to avoid the incoming flurry from the experts as to why that makes no sense).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 12, 2018, 12:03:46 PM
OK, fair enough.

Maybe a dumb request, but since I've found some contradictions on the net, here goes...

Would it be possible to indicate the lug 1 for the pots on the schematic? I could never get my head past volume controls where that's concerned. Just seems that the conventions for this are all over the map.

Well now you know how to decode Merlin's dialect, wherever you see CCW, you can translate to lug 1.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 12, 2018, 12:10:43 PM

Well now you know how to decode Merlin's dialect, wherever you see CCW, you can translate to lug 1.


Yup, got it. Thanks Sam. :icon_biggrin:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 13, 2018, 01:36:41 AM
I label the pins on a potentiometer CCW, W and CW for counterclockwise, wiper and clockwise. On the schematic symbol I show the wiper off center so you can see visually which end is clockwise. I label the pins on a SPDT switch NO, C and NC for normally open, common, and normally closed. I label the pins on a diode A and K for anode and cathode (kathodos). I label the pins on a jack socket T for tip, R for ring and S for sleeve. And so on ad infinitum.

For multiple gang parts I just append numbers 0, 1, 2 etc to this nomenclature. Pin numbers are always confusing IMHO. Some people number the pins of a TO92 transistor looking from the top, some looking from the bottom. Some people even put pin 3 in the middle. This is how it is with SOT-23 packages. It's all rather confusing and I try to do everything I can to make it hard to make a mistake. Even so I still make plenty of mistakes.  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 13, 2018, 06:33:26 AM
Wiper biased to the CW side. Check. Greatly appreciated.

That was
(https://pamgrout.files.wordpress.com/2018/03/easy.jpg?w=400&h=400)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 13, 2018, 10:18:47 AM
jonny, can the treble boost be incorporated into the new design? It's one of the features that I really appreciate on the original design, especially with humbuckers.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: samhay on June 13, 2018, 02:15:32 PM
^It's already there via C7 and R9.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 13, 2018, 09:29:59 PM
Another convention: an arrow showing which way the slider moves for "more".

(http://2.bp.blogspot.com/-5PpPTHeZnhA/UTlfBmDFg4I/AAAAAAAAMKg/_mqnlFx9XIM/s320/05.jpg)

(https://s33.postimg.cc/4kquhahe7/component-potentiometer-symbol-schematic-resistor-gaussmarkov-di.png)

(Remember that CW and CCW are sometimes relative. Gas stove knobs are CCW for "more". The old Quad hi-fi had only part of the knob exposed, and internally turned withershins. Ham equipment sometimes have right-angle gear drives.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: suryabeep on June 16, 2018, 09:06:44 PM
Hello!
I built a 5-knob version with the treble boost switch. Everything works fine, except the LED. It's off when the effect is on (I can tell because the knobs change the sound), and on when the effect is off. How can I fix this?
I'm using a 2n7000 flipped 180 degrees in place of the BS170.
(https://s15.postimg.cc/61xyyy8hj/Screen_Shot_2018-06-16_at_6.03.57_PM.png) (https://postimg.cc/image/61xyyy8hj/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on June 18, 2018, 07:44:38 AM
Another convention: an arrow showing which way the slider moves for "more".

(http://2.bp.blogspot.com/-5PpPTHeZnhA/UTlfBmDFg4I/AAAAAAAAMKg/_mqnlFx9XIM/s320/05.jpg)

(https://s33.postimg.cc/4kquhahe7/component-potentiometer-symbol-schematic-resistor-gaussmarkov-di.png)

(Remember that CW and CCW are sometimes relative. Gas stove knobs are CCW for "more". The old Quad hi-fi had only part of the knob exposed, and internally turned withershins. Ham equipment sometimes have right-angle gear drives.)

And yet... the schematic you post also shows the pot lug numbers. For all intents and purposes, the arrows could simply be indicating the direction to Santa's workshop.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 20, 2018, 06:57:12 PM
I finished my latest batch of changes to the gate design. I added a new peak detector, and a threshold comparator with some hysteresis. I also added separate attack and release controls for the noise gate. It's now an 8 knob monster :icon_cool:

Here is the schematic:
(https://s33.postimg.cc/r3x63rxyz/Capture.png) (https://postimg.cc/image/r3x63rxyz/)

Here are some photos of the revision C PCB:
(https://s33.postimg.cc/rhyi2tcrf/IMG_20180620_152517747.jpg) (https://postimg.cc/image/rhyi2tcrf/)
(https://s33.postimg.cc/nll66tzhn/IMG_20180620_152533863.jpg) (https://postimg.cc/image/nll66tzhn/)
(https://s33.postimg.cc/bz125vc8b/pcb.png) (https://postimg.cc/image/bz125vc8b/)


Here it is in action. Sorry for the poor audio quality, it's just my phone camera, which is adding some weird compression of its own to the sound :(
One day I'll get a proper camera and mic for this stuff.


Overall I am fairly happy with the circuit design. It's a bit more complex than I would have liked, and at 100 x 70mm will no longer fit inside a 1590B (you need a 1590BB instead), but the added flexibility to the noise gate is nice. Let me know if you would like a PCB to build yourself.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: suryabeep on June 20, 2018, 10:52:29 PM
I finished my latest batch of changes to the gate design. I added a new peak detector, and a threshold comparator with some hysteresis. I also added separate attack and release controls for the noise gate.

  :o WOW! I can't even begin to comprehend what's going on in this circuit. Could someone please explain how the gate works and what Hysteresis is? (or provide some links if possible)
Amazing stuff Jonny!
PS - can I replace all those 1uF caps with something smaller like a 100n? 1uF's are kinda expensive compared to 100n, especially when using so many  ;D
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 21, 2018, 04:59:05 PM
Could someone please explain how the gate works and what Hysteresis is? (or provide some links if possible)

OK here is a brief description of how the circuit operates 8)

IC5 is a charge pump voltage inverter. It generates a negative voltage from a positive one by moving charge between a "pump" capacitor C21 and a "reservoir" capacitor C24. There is a lot of 10kHz ripple on the output. TR3 is acting as a lowpass filter to remove the 10kHz ripple from the negative supply rail.

When you have both positive and negative supplies, the rest of the circuit design gets simpler, as you only have one ground reference for all signals.

With a single supply, it's like only having unsigned integers in your computer. Everything is still possible but you have to think a lot more about how to implement simple things. I generally prefer to generate a -8V rail rather than split the voltage and create a virtual ground at 4.5V. Not only do you get more headroom, but you can fill the top of the PCB with ground plane which improves noise performance, since real ground and signal ground are the same net.

TR1 is a n channel JFET configured as a source follower. It is basically a unity gain buffer which turns the high impedance guitar input into a low impedance signal. You could make a buffer in lots of ways. I happen to like the sound of this J112 buffer with single coil guitars, and I expect this pedal to be first in my effects chain.

IC1A is an inverting amplifier. So is IC1B. IC2 is an operational transconductance amplifier (OTA). https://en.wikipedia.org/wiki/Operational_transconductance_amplifier (https://en.wikipedia.org/wiki/Operational_transconductance_amplifier) Its transconductance is proportional to the control current into pins 1 and 16. In this circuit, it is set up to be a virtual feedback resistor around IC1A. The higher the control current, the lower the virtual resistance, and the less overall gain (due to the lower feedback resistance). So basically gain reduction is proportional to the current flowing into pins 1 and 16. You could just use one half of the LM13700 as in Merlin's original circuit, but paralleling them up like this reduces the noise a little, and since you get 2 in a package you might as well.

IC3 is the compressor sidechain. I have not changed this from the original design, other than adapting it for a bipolar power supply. IC3A is a negative peak detector, with separate attack and decay time constants. It produces a negative voltage on C13 that represents the peak value of the input signal. R20 and C11 further smooth this voltage. IC3B and TR2 convert the voltage into a current. R12 sets the conversion ratio, in this case 1mA / volt. So overall, the gain reduction is proportional to the input signal amplitude. Bingo - compression! In my opinion it is the slightly unusual feed-forward sidechain peak detector that gives the engineer's thumb its signature sound, which I like so much. You can really experiment with the character of the compressor by trying different dual opamps in place of IC3.

IC6 and IC4 are the noise gate sidechain. The noise gate works by setting the gain reduction to a maximum (max current into IC2 control inputs).

IC6A looks familiar to anyone who has built a tube screamer. It is just a high gain clipping circuit, so that even very low level signals are amplified enough to open the gate. IC6B is an inverting amplifier with a gain of -1.  D8, D9, C26 and R28 form a peak detector for peaks of either polarity. It is important with a noise gate to detect both positive and negative peaks so the gate opens fast enough. This doesn't matter so much for a compressor hence the half wave level detector for the compressor sidechain.

IC4A is set up as an inverting threshold comparator. When its input signal is strong, the output goes low and the gate opens. When the input signal is weak, the output goes high and the gate closes. R26 provides hysteresis (positive feedback) so that the threshold to open the gate is about 4dB higher than the threshold to close the gate. This Schmitt trigger stops the gate from chattering as the note dies away. https://en.wikipedia.org/wiki/Schmitt_trigger (https://en.wikipedia.org/wiki/Schmitt_trigger)

R23 and C17 are there to slow the edges of the transitions to avoid audible clicks when the gate opens and closes. D5, D6, RV4, RV6 and C15 make up the gate attack and decay time constants. IC4B is just a buffer to supply current into the control pin of the OTA, and hence control gain reduction. D7 is there to make sure that IC4B only sources current, and never sinks current from TR2. LED5 glows when gain reduction is being applied, either by the gate or the compressor. Its brightness is roughly proportional to the amount of gain reduction being applied.

I hope this helps  :)
Jonny

PS: 1uF and 10uF ceramic capacitors are just a few cents each when you buy them in bags of 50 or 100 off eBay. I tried 100n in the circuit and it lets some control clicking into the audio path which you can hear with high gain sounds. I recommend using 1uF ceramics for decoupling as shown. Why spoil the performance of the circuit for a saving of less than a dollar? These are what I used for my build. I measured them with my LCR meter and they are really good. Loss factor less than 0.1% and ESR less than 0.1 ohms. Ideal for the application. With multilayer ceramic capacitors it is always a good idea to get voltage rating much higher than the circuit voltages, as this type of capacitor decreases in value when significant bias voltage is applied. I typically use 50V parts for stompbox circuits.
https://www.taydaelectronics.com/1uf-50v-multilayer-ceramic-capacitor.html (https://www.taydaelectronics.com/1uf-50v-multilayer-ceramic-capacitor.html)
https://www.ebay.com/itm/50pcs-Monolithic-Ceramic-Chip-Capacitor-1uF-105-50V-Pitch-5-08MM-New-M/321389847401?hash=item4ad453e369:g:-E0AAOxycD9TW82M (https://www.ebay.com/itm/50pcs-Monolithic-Ceramic-Chip-Capacitor-1uF-105-50V-Pitch-5-08MM-New-M/321389847401?hash=item4ad453e369:g:-E0AAOxycD9TW82M)
https://www.ebay.com/itm/50pcs-106-50V-10uf-10000nf-10000000pf-Multlayer-Ceramic-Capacitor/112250694765?hash=item1a22a9ac6d:g:GMoAAOSwux5YXhz7 (https://www.ebay.com/itm/50pcs-106-50V-10uf-10000nf-10000000pf-Multlayer-Ceramic-Capacitor/112250694765?hash=item1a22a9ac6d:g:GMoAAOSwux5YXhz7)


(https://s33.postimg.cc/r3x63rxyz/Capture.png) (https://postimg.cc/image/r3x63rxyz/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: suryabeep on June 23, 2018, 05:59:19 PM
I modified the original schematic to include the paralleled OTAs, however I am not sure if this is correct. Could someone take a look and tell me if this will work?
I simply took the 'parallel' configuration from jonny's schematic and applied it to the original schematic without changing anything else.
Also, at the risk of repeating myself (since my original seems to have gotten lost in the replies): the indicator LED on my ET build is on in bypass and off when the effect is engaged. How can I fix this?
(https://s8.postimg.cc/d08sqztr5/et_paralleled.png) (https://postimg.cc/image/d08sqztr5/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 24, 2018, 02:09:29 AM
You've got the OTA incorrectly wired. The ouput should connect to the inverting input of the opamp. R7 is 220 ohms in the original circuit. You need to move LED1 and R19 to the drain of Q2.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: suryabeep on June 24, 2018, 11:46:27 AM
Thank you!
So, like this then?
(https://s22.postimg.cc/a0zs7e831/Screen_Shot_2018-06-24_at_8.45.39_AM.png) (https://postimg.cc/image/a0zs7e831/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 24, 2018, 03:03:02 PM
Closer. What is R3 for? I think you'd be better off without it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 25, 2018, 05:44:50 AM
Thank you!
So, like this then?
(https://s22.postimg.cc/a0zs7e831/Screen_Shot_2018-06-24_at_8.45.39_AM.png) (https://postimg.cc/image/a0zs7e831/)
Correct. R3 is not essential. I included it in my original design as an attempt at stabilisation, but it turned out not to need it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on July 08, 2018, 09:21:16 PM
Here is my engineer's thumb redux in a case. It sounds really sweet now. All the residual noise went away when I put it in an aluminum enclosure. I connected the case to the PCB ground plane.
(https://s33.postimg.cc/55vx9mxgr/IMG_20180708_182954339_HDR.jpg) (https://postimg.cc/image/55vx9mxgr/)
(https://s33.postimg.cc/6xow4m94r/IMG_20180708_183303995_HDR.jpg) (https://postimg.cc/image/6xow4m94r/)
This is the final circuit revision I ended up with after a bit of value tweaking with different guitars.
(https://s33.postimg.cc/a39hutzgr/Capture.png) (https://postimg.cc/image/a39hutzgr/)
I have a few spare PCBs. Let me know if you would like to build one.




Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ben N on July 09, 2018, 08:09:07 AM
Been following this thread along. What can I say about Merlin's little compressor? It grew some! Now that it is a super-flexible uber-comp, maybe the last two things to add are a separate side-chain input (to facilitate placement anywhere in the signal chain, so long as the envelope detector and gate get fed a clean, dry signal) and MIDI control.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: EeroN on July 15, 2018, 06:24:01 AM
Hi all,

I built an Engineer's thumb a few years ago and it works great. However, I'd like to get a bit more level boost from the circuit, not much but I find I almost need to max out the Level control to match the bypassed signal.

I know how to adjust the gain of a typical opamp circuit, but I'm not sure how I should go about it with the OTA in the feedback loop, so as to not mess up the compression effect.

Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: auden100 on July 15, 2018, 12:26:39 PM
I had a similar issue. This was the reply at the time.

Is there any thing in the circuit that could be changed that would provide more volume?

I *think* if you change R8 from 220R to 100R you will get a 6dB boost.
:icon_surprised:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: EeroN on July 16, 2018, 02:47:11 AM
I had a similar issue. This was the reply at the time.

Is there any thing in the circuit that could be changed that would provide more volume?

I *think* if you change R8 from 220R to 100R you will get a 6dB boost.
:icon_surprised:

Thanks! I'll try that, it's easy enough to tack another 220 in parallel and see what happens.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: EeroN on July 17, 2018, 06:08:57 AM
Yeah, that did it.

Thanks!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: suryabeep on August 02, 2018, 01:00:53 PM
Hello!
I built an engineers thumb redux as made by jonny.reckless,  but it is not working. Bypass works fine, but switching it on creates a very loud pop (even though I'm using a switching board that has almost eliminated that from all my other builds). There is no sound when I'm strumming at a low volume, but strumming hard produces a loud crackling noise. I can't really tell if the gate on/off switch is having any effect on the noise.
I've gone over the bottom of my board for any solder bridges - none so far.
Here are my voltages:
MAX1044 pins 1-8:
4.57, 4.63, 0, -4.16, -8.22, 4.69, 4.51, 9.32
TL072 1-8:
-4.89, -4.59, 0, -7.29, -4.65, -3.44, -4.54, -5.36
LM833 1-8:
8.44, 8.47, 8--(decreases when I probe it), -7.22, 0, 2.91, -6.21, 9.58
TL074 1-14
-6.29, -5.73, 0, -6.78, 0, -6.33, -6.33, -6.25, 0, 0.56, -7.27, -0.20 (increases slowly to 0), -6.32, -6.31
LM13700 1-16
-6.31, -0.01, 0.18, 0, 8.47, -7.26, 0,0,0.01, 0, 9.57, 8.47, 0, 0.18, -0.01, -6.31
J201 dsg:
9.57, 9.57, 7.25
BC556 (Q3) EBC:
-3.44, -4.19, -3.45
BC556 (Q1) EBC:
-7.28, -7.98, -8.20

I've never had to troubleshoot anything this complicated before, so I don't even know where to start :(
The schematic i'm using is attached below.
Thanks!
(https://s33.postimg.cc/btnr2hsaj/redux_schematic.png) (https://postimg.cc/image/btnr2hsaj/)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 03, 2018, 05:15:23 AM
I've never had to troubleshoot anything this complicated before, so I don't even know where to start :(
The schematic i'm using is attached below.
Thanks!
(https://s33.postimg.cc/btnr2hsaj/redux_schematic.png) (https://postimg.cc/image/btnr2hsaj/)
Those numbers hurt my eyes. Maybe you could write them on the schematic itself, in the relevant locations, and reattach it? Preferably in a new thread.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on August 03, 2018, 04:16:08 PM
> The schematic i'm using is attached below.

Has errors. Missing a ground under LED1 LED2, which is why the JFET voltages are all jammed high.

The parts with more than 3 legs, it is just too tedious to have one finger in your listing counting pin numbers and the other finger on the plan.

And Merlin has a point. This is not *his* ET but a different (derived) project, and maybe best kept apart.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: domestic-bliss on August 03, 2018, 05:43:45 PM
Hi everyone.... new member [but played guitar on off and always been into effects/tone in general since probably about well 1992 aged 8 lol]
realy want to build the all singing all dancing version of this [with noise gate etc and as best as possible for metal]
I want to use it along with a diy [hopefully although might buy a cheap one and mod it who knows open to suggestions here] tube screamer.....
I play metal [almost djent tbh think obsolete/demanufacture ish era fear factory with a dash of type o yes im a weirdo]
 so the usual convention is ....
guitar [with obligatory emg81] - noise gate - compressor  - tube screamer - amp - and an eq in the fx loop.....................
would putting the redux engineers thumb and a tube screamer type unit in one box to go in front of the amp [il be actualy using a line 6 x3 live hopefuly but wel call it the amp for now] be doable?
i see there is a few variable options available which would probably suit me better ?
realy liking this engineers thumb .............. and my close friends circle are not strangers to electronics
massive thanks to all in this forum ive learnt a ton in the day or two ive known about it lol
:-)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on August 04, 2018, 03:44:26 PM
Hello!
I built an engineers thumb redux as made by jonny.reckless,  but it is not working.
(https://s33.postimg.cc/btnr2hsaj/redux_schematic.png) (https://postimg.cc/image/btnr2hsaj/)

In your circuit you are missing the feedback around IC2A. There should be 220 ohm and 10uF in series to ground from the inverting input. The gate won't open without the extra gain. This stage has a gain of several thousand at max.

I think you have also got the +9V to the op amps wired up incorrect. The supply goes to the opamp pin, and the decoupling cap goes from the pin to ground. As shown the decoupling cap is in series with the positive supply.

The input stage ground is missing. Pin 3 of IC3 needs to be grounded. There may be other issues.

I have a fully debugged PCB available if you want to build one. The layout is important if you want to avoid parasitic oscillation or poor noise performance.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: thehallofshields on August 05, 2018, 05:55:53 PM
I've built 2 of these now that didn't work.  :(

When 'Ratio' is cranked up, I'm just getting clean + background fuzz with no compression.
I'm hoping that the problem is a bad batch of CA3080 chips.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: thehallofshields on August 05, 2018, 06:15:38 PM
I'm set on using pots instead of toggles for this build, so I'm going to try this treble control.

(http://i66.tinypic.com/2hmhgl5.png)

If it doesn't have enough of an effect, I'll just put the Treble Boost mod as always on, then put a passive Tone Control at the end of the circuit.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on November 05, 2018, 10:36:25 AM
Hi guys, I need help with this compressor.
I'm using the sabrotone veroboard layout, and I included even the two leds that was missing.
I got a bump when I switch the effect, the noise is an high pitch snap amplified from the compressing, indeed with Ratio at zero I have no bump.
I tried to use a 1M resistor from input to ground, but it didn't solve.

Please help, the pedal is for a friend.

Edit: If I put a Jan Ray clone after it I can reduce the bump, but a pull down resistor in the input or in the output, 1M or 39k, don't solve it.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on November 28, 2018, 09:45:32 AM
Hello,

I've just read the near 30 pages here and Valve Wizards web page for version II, and I'm pretty much all set, but can I just ask, if I have understood things correctly, it appears that the Threshold and Ratio controls have a similar effect, for those that have built it and used this compressor, is there an advantage to having both the Ratio and the Threshold control? I'm not adverse to putting in the extra pot, but if they effectively achieve the same end result, I'd rather keep it to just four knobs and stick to the 1M resistor for the threshold.

Many thanks, Chris

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on November 28, 2018, 02:32:21 PM
I've built 2 of these now that didn't work.  :(

When 'Ratio' is cranked up, I'm just getting clean + background fuzz with no compression.
I'm hoping that the problem is a bad batch of CA3080 chips.

Don't bother using CA3080 ICs, they're most probably fake. Use LM13700 in parallel.

How did your "tone" pot work?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on November 28, 2018, 04:45:08 PM
> the Threshold and Ratio controls have a similar effect

They do quite different things, at least for wide dynamic range input.

Look at another "compressor". You want to have a parade. You do not want tall-and-short marchers and a lumpy mob, you want all about the same height.

Threshold: anybody under this height we leave alone.

Anybody over the threshold, we cut some off the top.

Ratio: A 2:1 ratio we cut half the excess. A 10:1 ratio, we cut 90% of the excess.

_I_ would go ahead, blow the buck, have all likely knobs on my first build. Perhaps after extended playing, I might find one or the other can be left pre-set. But until you play a lot (on many types of music) you can't be sure.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on November 29, 2018, 10:53:06 AM
Thanks PRP,

Your explanation on how the two controls differ is very useful, the only reason for me asking the questions is this post from Merlinb:

Just wondering what it is about the design that means the threshold control isn't really worthwhile.
Basically because it is soft-knee compression. When you're operating in and around a soft knee, turning down the threhold has a very similar effect on the transfer function as as turning down the ratio. You can see that to the left of the red line (i.e. around the knee) both graphs look very nearly the same, so if your signal spends most of its time in this region, you won't notice the difference between using the threshold control or the ratio control.
(http://i81.photobucket.com/albums/j207/merlinblencowe/text3940_zpsx4vqiaem.png)

But I'll take your advice and build the five knob version, this will be my first project designing a PCB layout! so a lot of learning and no doubt mistakes ahead.

Thanks again, Chris
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on December 02, 2018, 11:09:49 AM
Hello,

I'm drawing out the schematic for a five knob version of the Engineer's Thumb V2 in Eagle, and I'm struggling with the potentiometers, particularly the threshold knob, knowing whether pin 1 or pin 3 is connected to the 4.5v rail.

The data sheet for the Alpha pot https://www.rapidonline.com/pdf/561734_v2.pdf (https://www.rapidonline.com/pdf/561734_v2.pdf) numbers the pin as shown in my photo:

(https://i.postimg.cc/BPZnpH4t/Pot-01.jpg) (https://postimg.cc/BPZnpH4t)

And here is that section of the schematic I've drawn out:

(https://i.postimg.cc/8FkX1CpM/Pot-02.jpg) (https://postimg.cc/8FkX1CpM)

It would be most helpful if someone could say whether I have got the threshold pot the right way round in the schematic or not. I think the other pots are correct, but happy to told otherwise. My plan is to use PCB mounted pots so it would be nice to get it right first time.

Many thanks, Chris
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on December 02, 2018, 11:45:34 AM
I've put CCW (1) to 4.5V and CW (3) to C3, so I believe your schematic is OK.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on December 02, 2018, 05:40:11 PM
> knowing whether pin 1 or pin 3 is connected to

See the arrow on each pot symbol? This points to the "full up" end of the pot travel.

(I could swear we had this debate already, maybe in this thread.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on December 03, 2018, 03:49:25 AM
I'm struggling with the potentiometers, particularly the threshold knob, knowing whether pin 1 or pin 3 is connected to the 4.5v rail.
Threshold is a funny one because some people will expect the threshold to be raised as you turn the knob clockwise; like, give it more threshold, man. That means compression kicks in later.
But some people expect knobs to 'do more effect' as you rotate clockwise. That means you want the threshold to lower; like, give it more sensitivity, man.

Which you choose is up to you. If you want the threshold to raise as you turn clockwise, 4.5V goes to CW pin (3).  Otherwise it goes to the CCW pin (1). Guitarists notoriously don't know how to use compressors, so I would choose the latter for a stompbox, and the former for a studio compressor.

EDIT: Not sure if that was the question you were asking  :icon_redface:

Quote
My plan is to use PCB mounted pots so it would be nice to get it right first time.
You can check for yourself when you lay out the PCB, since you will see the 4.5V net connecting to one pad or the other. You can always switch back to the schematic and reverse the connections.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: bluebunny on December 03, 2018, 03:57:56 AM
Guitarists notoriously don't know how to use compressors

I lent my ET (and some others) to my tame guitarist to try out...

TG: It doesn't sustain as much as my xxx compressor.

BB: There's no such thing as sustain (explains what compressors actually do...)

TG: It doesn't sustain as much as my xxx compressor...


:icon_rolleyes:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on December 04, 2018, 03:57:41 AM
Thank you all your your help, I'm sort of relieved that which ever why the threshold pot goes in I can argue the case that it's the correct way!

Last night I had my first attempt at laying out the PCB, this was the first time I've done anything like this and I now have renewed respect for people who have produced beautifully laid out PCBs, it was daunting and frustrating at times. With a lot of vias and a number of tracks that go round three sides of the board to join components it did all join up in the end, but I plan to have another go tonight to see if I can do it better.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: digi2t on December 04, 2018, 11:32:49 AM
A question regarding the Threshold pot. This one has always vexed me...

Would it be wrong to flip it around, i.e. pin 3 to the vref? That way, it would act as somewhat of a "sensitivity control" instead? Big signal inbound, turn it down, small signal inbound, turn it up?

Just looking at it from a different perspective I suppose, or am I out to lunch on this one? :icon_rolleyes:
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on December 04, 2018, 01:26:30 PM
On Merlinb's schematic there are three 1uf electrolytic capacitors, do these have to be electrolytic caps?

The reason I ask is that I have some 1uf polyester box capacitors in stock from the last pedal I orders parts for, and I have some 1uf electrolytic caps on order, and I'm looking at the schematic trying to decide if electrolytic caps were chosen because they have properties that make them better suited?

I then took a sneak peek at Merlinb's web store, and saw he has some PCBs for sale and was looking for a bit of inspiration on my PCB layout, I realised there didn't seem to be enough round electrolytic caps on the silk screening... Then I spotted a couple of + signs next to another couple of capacitors, so I assume these missing electrolytic caps have been replaced by tantalum caps.

In trying to further my understanding of how electronics work, I'd be grateful to know if in the position where these 1uf caps are placed, is there something about them being polarized that is important?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on December 04, 2018, 02:46:12 PM
Last night I had my first attempt at laying out the PCB, this was the first time I've done anything like this and I now have renewed respect for people who have produced beautifully laid out PCBs, it was daunting and frustrating at times. With a lot of vias and a number of tracks that go round three sides of the board to join components it did all join up in the end, but I plan to have another go tonight to see if I can do it better.

You can buy PCBs from Merlin. http://valvewizard.co.uk/shop.html (http://valvewizard.co.uk/shop.html)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on December 04, 2018, 06:30:34 PM
Last night I had my first attempt at laying out the PCB, this was the first time I've done anything like this and I now have renewed respect for people who have produced beautifully laid out PCBs, it was daunting and frustrating at times. With a lot of vias and a number of tracks that go round three sides of the board to join components it did all join up in the end, but I plan to have another go tonight to see if I can do it better.

You can buy PCBs from Merlin. http://valvewizard.co.uk/shop.html (http://valvewizard.co.uk/shop.html)

I know:

I then took a sneak peek at Merlinb's web store, and saw he has some PCBs for sale and was looking for a bit of inspiration on my PCB layout....

I built a compressor pedal many, many years ago from a kit that was featured in a UK guitar magazine, the compressor was call the "Paranormal" however there is something wrong with it now and it's eating the same 2N7000 FET each time I replace it. My knowledge of electronics is minimal and I decided I wanted to learn more, so in the last month I've built two over drive pedals, one from a kit, and one from a bought PCB, but it's still painting by numbers... So I'm currently in need of a compressor, and Merlinb's design seemed simple with regards to the number of parts and yet exciting as it's a different design, and I thought that trying to create my own PCB from his schematic would be one step further to gaining some understanding. I also have the advantage of having access to my dad's old etch tank and UV box.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: highwater on December 04, 2018, 09:12:46 PM
On Merlinb's schematic there are three 1uf electrolytic capacitors, do these have to be electrolytic caps?

The reason I ask is that I have some 1uf polyester box capacitors in stock from the last pedal I orders parts for, and I have some 1uf electrolytic caps on order, and I'm looking at the schematic trying to decide if electrolytic caps were chosen because they have properties that make them better suited?

A 1uF electrolytic cap is going to be a LOT smaller and cheaper than a polyester cap. The polyester cap will be the same or better in just-about every other way.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on December 05, 2018, 02:17:09 AM
I built a compressor pedal many, many years ago from a kit that was featured in a UK guitar magazine, the compressor was call the "Paranormal" however there is something wrong with it now and it's eating the same 2N7000 FET each time I replace it. My knowledge of electronics is minimal and I decided I wanted to learn more, so in the last month I've built two over drive pedals, one from a kit, and one from a bought PCB, but it's still painting by numbers... So I'm currently in need of a compressor, and Merlinb's design seemed simple with regards to the number of parts and yet exciting as it's a different design, and I thought that trying to create my own PCB from his schematic would be one step further to gaining some understanding. I also have the advantage of having access to my dad's old etch tank and UV box.

There is a thread about that compressor here: https://www.diystompboxes.com/smfforum/index.php?topic=52905.0 (https://www.diystompboxes.com/smfforum/index.php?topic=52905.0), but lacks a schematic.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on December 05, 2018, 03:25:15 AM
On Merlinb's schematic there are three 1uf electrolytic capacitors, do these have to be electrolytic caps?
Tantalum, plastic/poly, or ceramic caps are preferred. Use electrolytic as a last resort.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: FlyingWild on December 08, 2018, 04:55:27 PM
Thank you so much for making this schematic available Merlinb, this morning I etched my first PCB and just now I turned it on for the first time, and it worked! Tomorrow I'll spend some time playing around to see what it can do, but from a quick twiddle of the knobs and some very poor guitar playing I can already say I'm very happy.

(https://i.postimg.cc/5YVSxVrj/Engineers-Thumb-04.jpg) (https://postimg.cc/5YVSxVrj)

(https://i.postimg.cc/p5NbVpHz/Engineers-Thumb-05.jpg) (https://postimg.cc/p5NbVpHz)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on January 27, 2019, 09:15:27 AM
Hi Merlin.
I collected information about compressors some time ago and came across your project again, I want to ask a couple of questions.
1) When comparing with the MXR, you indicate a number of advantages, including feedforward, what is its advantage over feedback?
2) In the side chain you use a half-wave rectifier, I saw a lot of circuits and they use a full-wave rectifier, why did you decide to restrict yourself to only half a wave?
3) Maybe earlier I asked this question, but still I will clarify, at the circuit input there is a capacitor with a small capacity, only 10 nanofarads, will this not be too small a value?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 28, 2019, 10:10:11 AM
1) When comparing with the MXR, you indicate a number of advantages, including feedforward, what is its advantage over feedback?
As explained on the webpage:
Feedback compression is simpler to arrange but technically inferior as it carries the massive disadvantage that you get overcompression on long attack times. In other words, the sound goes unnaturally quiet just after a loud transient, and then slowly returns, creating annoying pumping effects. This is why most pedal compressors don't let you control the attack- it is set permanently fast. With feedforward compression you don't get this problem, so you can have any attack time you want.

Quote
2) In the side chain you use a half-wave rectifier, I saw a lot of circuits and they use a full-wave rectifier, why did you decide to restrict yourself to only half a wave?
Full-wave requires an extra opamp.

Quote
3) Maybe earlier I asked this question, but still I will clarify, at the circuit input there is a capacitor with a small capacity, only 10 nanofarads, will this not be too small a value?
Too small for what? Does your guitar go down to 16Hz?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on January 28, 2019, 04:42:44 PM

1) Thanks again
2) Yes, it would require another operational amplifier, but wouldn't it be the best solution? Indeed, many modern solutions have a full-wave rectifier.
3) Yes, you are right, I did not carry out a calculation, I just got used to seeing that all the schemes use 47 nanofarads or more.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on January 29, 2019, 01:33:44 AM
> I did not carry out a calculation, I just got used to seeing that all the schemes use 47 nanofarads or more.

Why do "all" use 47nFd? Because they do not carry out the calculation!

What is it driving? 1 Meg plus two FET inputs (>100Meg). I don't even calculate that; I "know" 0.01uFd (10nFd) into 1Meg is 17Hz. Which is often good enough for wide-range High Fidelity. And certainly ample for guitar.

A fancier rectifier. I'm a big fan of excellent rectification in studio and concert-hall recording limiters. My experience in AM transmitting showed that some sounds are asymmetrical. But mostly male speech. There are other advantages. But half-wave gets you 90% of the benefits for less than half the cost.

Cost can be several things. The main thing I see looking at the ET is how few chips it uses. And how that simplifies the build. You know that half the people here would struggle with anything which had more parts. Builder time and struggle is part of the cost.

There is NO END of ways to "improve a limiter with more parts". It is a bottomless pit. On the one hand you can do a limiter with 5 parts around a power amp. At the other end, well, the EMT 266X comes very close to falling in the pit. Blesser spent over a year putting features into it. The box is stuffed with boards stuffed with parts. The knobs adjust every maybe-useful aspect of dynamics. Nobody has tried all settings. More to the point: it was very expensive to build, and unsurprisingly it has been hard to keep working over the decades.
https://www.bn1studio.co.uk/wordpress/wp-content/uploads/2018/11/0151680.jpg

Another over-kill limiter is the Fairchild 660. Weighs more than most large guitar rigs.

You have to find your market point. Do you want a Kia Trio? A Toyota Corolla? A Bentley? A Lamborghini? Yeah, the Lambo is cool, but often the Toyota is a fine choice.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: garcho on January 29, 2019, 03:21:11 AM
Yeah but the Fairchild has big knobs, big knobs = better
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on January 29, 2019, 03:52:19 AM
2) Yes, it would require another operational amplifier, but wouldn't it be the best solution? Indeed, many modern solutions have a full-wave rectifier.
(https://pics.me.me/there-are-no-solutions-there-are-only-trade-offs-thomas-sowell-20076941.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: POTL on January 29, 2019, 10:16:07 AM
I agree
Each design has its advantages and disadvantages.
Many vintage schemes, such as the Univibe and 1176 nowadays can be constructed using fewer components.
This is a way of obtaining knowledge, theoretical and practical, as well as a variety of experiments.
I am always happy to receive information from experienced people and it is most pleasant to receive it from the author of the scheme in order to understand how he is guided when making certain decisions, I learn and are happy to receive new information, including the one that does not always lie on the surface, it only appears with experience and it’s wonderful that many experienced people are willing to share knowledge here.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ben N on February 10, 2019, 05:23:18 PM
Yeah but the Fairchild has big knobs, big knobs = better

QED!

Ed: On second thought, is this argument some kind of portal back to the Burst Box thread?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on May 30, 2019, 12:17:43 PM
hi guys, just built the ET....cool comp. nice work merlin.  8)

just asking if anyone put the ''comp led indicator'' led in theirs and it worked ok.

as in PRR's led mod here.
https://www.diystompboxes.com/smfforum/index.php?topic=97123.msg1031906#msg1031906


cheers rob .
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on May 30, 2019, 03:09:28 PM
I tried that LED indicator, but wasn't too satisfied with that. Can't remember all the reasons, it was long time ago.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on May 30, 2019, 03:47:52 PM
Cheers man, I,ll just tack it on and try it .....see how it goes.
Title: Compression indicator LED
Post by: merlinb on May 31, 2019, 03:12:33 AM
Last night I had an idea for a different way to add a compression indicator LED. The 4.5V ref only has to supply significant current when the circuit is compressing, so you can just add the LED to the output of the Vref buffer (note that it is inside the feedback loop). I suggest using a super-bright LED since the current variation is between 0 and 2mA at most. What's nice about this approach is that it doesn't use any extra battery power.

EDIT: It worked best for me with a blue or white LED since they were both superbrights. These were so efficient they were dimly lit even with no signal, but if you want to tame this then try adding a resistor in parallel with the LED and adjust to taste (a few k-ohms probably). Most standard LEDs were too dim when I tried it, although one red one was 'OK'.

(https://i.postimg.cc/QB7NLFZ3/ET-comp-LED2.jpg) (https://postimg.cc/QB7NLFZ3)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: deadastronaut on May 31, 2019, 03:31:31 AM
cheers merlin, i'll give this a go then......report back later.  8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Rob Strand on May 31, 2019, 03:57:10 AM
Quote
Last night I had an idea for a different way to add a compression indicator LED.
I like the idea.  You might get some glitching on the 4.5V rail.  I thought PRR's solution was fine also and perhaps less susceptible to glitching the 4.5V rail.

I think it's going to have the same problems as PRR's solution as far as the LED dimming is concerned; see the comments around the PRR's solution via deadastronaut's link.   

I believe the solution is to put a resistor across the LED, say around 2k2 to 4k7 for yours and maybe lower for PRR's; you will need to experiment.   The idea is when the LED current reaches a minimum threshold it goes out.   Suppose we set the point where it LED extinguished at 0.5mA then the resistor needs to be R = VLED/I_threshold = 1.7V/0.5mA = 3.4k.  When the current drops below the threshold the resistor hogs the current and there's not enough voltage to light the LED.

I've actually used this method for simple battery chargers.

The problem is it's a *compressor* so you have to decide at what point you consider it not-compressing.   If the LED circuit is moved earlier on in the the ckt then you can trigger the LED when the rectifier pumps significant charge into the storage cap.   When the input signal drops there's a natural cut-off, in fact in this case you might need to extend the LED drive time.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 31, 2019, 04:29:44 AM
I think it's going to have the same problems as PRR's solution as far as the LED dimming is concerned; see the comments around the PRR's solution via deadastronaut's link. 
There was no problem with dimming. That LED lights according to the gain reduction, and the gain reduction releases slowly (or as fast as you choose to set it to) -that's how compressors work.
If you only want an LED to light when you're actually making a noise then you're talking about a signal presence indicator (e.g. sound2light), not a gain reduction indicator.
Quote
he problem is it's a *compressor* so you have to decide at what point you consider it not-compressing.
The comrpessor already does that for you. When the signal is below about 30mVpk it is below threshold, so there is no gain reduction (after the release time) and the LED will go out by itself.
But you can, of course, decide not to let the LED cover the full range of gain reduction, that's up to you. It depends if you just want it to 'look cool' rather than 'show what the compressor is actually doing'.

Now, I suppose I should remind everyone that this is a feedforward compressor, so the side chain is always working at full bore. But the ratio control works like a blend control, mixing compressed with uncompressed. That means even if you have the ratio control set to 'no compression' the side chain is still doing gain reduction as usual, so the LED will still light even though the output signal is purely clean. The LED only tells you what the side-chain / OTA is doing, it can't second-guess what you've set the ratio control to....
...unless you use a dual gang ratio pot and use the other gang to control the LED somehow. Or if you build the ET with the threshold control instead of a ratio control, but that incurs a noise penalty since it now must run at full ratio all the time.
(https://pics.me.me/there-are-no-solutions-there-are-only-trade-offs-thomas-sowell-20076941.png)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Rob Strand on May 31, 2019, 05:42:38 AM
Quote
But you can, of course, decide not to let the LED cover the full range of gain reduction, that's up to you. It
depends if you just want it to 'look cool' rather than 'show what the compressor is actually doing'.
For most compressors and limiters it's more conventional to blip the LED when the threshold is exceeded.  If you are in a long section of high input the blips and re-triggers are packed in close enough that the LED is on all the time. 

I don't have a problem with either method.  It's only a problem if you expect/want one thing but it does the other.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tristanc on June 15, 2019, 02:21:11 PM
On Merlinb's schematic there are three 1uf electrolytic capacitors, do these have to be electrolytic caps?
Tantalum, plastic/poly, or ceramic caps are preferred. Use electrolytic as a last resort.
What's the impact if I've used electrolytics for the two 1uFs to ground next to the Attack control? Anything major?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Elijah-Baley on June 16, 2019, 03:15:20 AM
For a value like 1uF, if you want, try polyester cap. Pay attention to the size.

I just boxed my Enginee's Thumb. But I'm not so happy about it. I built it twice, and both my boards (Sabrotone Layout at 5 knobs, but I included the LEDs) work weird. After the release time the volume rise up louder, and the first attack of the note, indeed, is really loud before the compression. Then, when the compression is high I get more volume from soft touch than the hard picking of the string. Very unnatural playing.
I used a resitor as Release control at 512k. And I could use neither the Threshold pot, but I used two resistors, but not exactly as the pot was in a certain position, because the two resistors are kind asymmetrical, the sum isn't 1M. I dont' know, I tried to work it well I could. (I have the treble boost and the attack pot, even if I prefer it maxed.)
All this volume issue cause a pop when I engage and disengage the pedal. After my mods is a bit softer, but, after the release time, when the compression is not acting I can hear the click of the footswitch anyway.
Further I found the 1M pot for the Ratio excessive, because I get anough comression at half, and at higher setting I still have the volume problem when I play soft and hard.
I tried two different LM13700 bought from two different shop, too.

I'm very surprised that nobody have this same issue!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 16, 2019, 02:35:22 PM
What's the impact if I've used electrolytics for the two 1uFs to ground next to the Attack control? Anything major?

Technically, electrolytics have a higher series resistance and a lower self resonant frequency than other classes of capacitor. You have to form a subjective opinion about what that does to the tone and response. I tried electrolytic, multilayer ceramic and tantalum capacitors in this location when I was doing some experiments with my engineer's thumb. You can definitely hear the difference, although it is hard to describe. I quite liked a 1uF 63V electrolytic in parallel with a 100nF 100V box polyester. Paralleling up different types and value of capacitor tends to lower the ESR and the Q, and is a trick we use a lot for high frequency decoupling in digital circuit design, but it doesn't have a lot of effect at audio frequencies.

Tayda sells a 1uF ceramic cap for $0.12 so personally I think using an electrolytic here is a false economy.
https://www.taydaelectronics.com/capacitors/monolithic-ceramic-capacitor/1uf-50v-multilayer-ceramic-capacitor.html (https://www.taydaelectronics.com/capacitors/monolithic-ceramic-capacitor/1uf-50v-multilayer-ceramic-capacitor.html)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ben N on June 16, 2019, 02:48:46 PM
Wow, a 1uf MLCC! Whodathunkit? I guess that's the solution for all the pcbs that don't leave enough room for the fat 1uf box film caps.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 16, 2019, 02:51:59 PM
I regularly use 1uF, 4.7uF and 10uF MLCCs in my designs. They're not expensive and work much better than electrolytics, especially for power supply decoupling and inter-stage coupling. I typically use box polyester for values between 1nF and 220nF, ceramics outside that, and electrolytics for bulk decoupling. I stopped using tantalums for audio a while back.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on June 16, 2019, 03:26:08 PM
Wow, a 1uf MLCC! Whodathunkit? I guess that's the solution for all the pcbs that don't leave enough room for the fat 1uf box film caps.

I have recently bought 10uF MLCC from Aliexpress, 100 pcs were around 1USD, and they're just fine. I use them now in all of my builds instead of 10uF electrolytics in non-audio parts of a circuit. Didn't try to use them for audio flow, however.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tristanc on June 16, 2019, 04:42:14 PM
I regularly use 1uF, 4.7uF and 10uF MLCCs in my designs. They're not expensive and work much better than electrolytics, especially for power supply decoupling and inter-stage coupling. I typically use box polyester for values between 1nF and 220nF, ceramics outside that, and electrolytics for bulk decoupling. I stopped using tantalums for audio a while back.
Thanks Jonny - this is really useful. It's this type of info I wish I had when making my pedal PCBs, but I guess it depends on the use case, so something like the below is an oversimplification:

1uF upwards - MLCC or electrolytic
1nF - 1uF - polyester
up to 1nF - ceramics

Perhaps even using the same footprints where possible.

I guess the question is if the difference warrants desoldering and swapping over in a tight situation...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: befey on September 05, 2019, 11:48:52 AM
Does anyone have any thoughts on how to add an external sidechain input to this?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 05, 2019, 01:10:36 PM
> external sidechain input


(https://i.postimg.cc/kVWJTz8m/TheEng.gif) (https://postimg.cc/kVWJTz8m)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: befey on September 05, 2019, 03:23:27 PM
Thanks so much! I'm still wrapping my head around how the different parts of this come together.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ben N on September 06, 2019, 09:33:30 AM
You'd probably want to use a switching jack on the sidechain input, so that it pulls the sidechain signal from the main input when there is nothing plugged into the external sidechain jack.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: befey on September 12, 2019, 12:47:14 PM
Based on the above, this is what I've come up with for a sidechain input that switches only when there's something plugged into the sidechain input. I'm unsure how to do the actual switching.

It also seems extra complicated to duplicate so much of the input stuff. Is there some way to eliminate some of that duplication?

<schematic removed>
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on September 13, 2019, 07:19:55 AM
Is there some way to eliminate some of that duplication?
Yes, use a switching jack socket:
(https://i.postimg.cc/PpymV239/sg.jpg) (https://postimg.cc/PpymV239)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: befey on September 13, 2019, 07:47:41 AM
I'm trying to have the threshold pot for both inputs. It looks like this schematic only has the threshold pot on the sidechain input?

Edit:  oh.... I think I can see that the normal input sends up to the sidechain, but gets interrupted when there's something plugged into the sidechain input?

And thanks for your help!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on November 12, 2019, 12:24:33 PM
I have a layout for the Engineer's Thumb Compressor that uses the CA3080. Both the two knob and the full version.
Transfer Template (2 knob) (https://drive.google.com/open?id=1D1ncIsOQQzFAfquuAIG8OGI-wmw_I7Ty)
My enclosure template (2 knob) (https://drive.google.com/open?id=1a1CsDdn0KM3UEROcuvozp1_lt0D3uk2q)
Transfer Template (full) (https://drive.google.com/open?id=1kLI-ywOojo3kdaOsycAJjUtZHja-40l-)
My enclosure template (full) (https://drive.google.com/open?id=1Rp9s8iZpj3OJ6zCGnW4_xkqwg7ccOLoi)

(https://i.postimg.cc/VkX9pTG0/COMP-FULL.png)

It has the LED indicator mod. If you don't want the LED, just omit it and replace the 1k above the pads with a jumper.
And of course - let me know if something doesn't look right. I'll be building this one next week.
-KM
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: snk on November 12, 2019, 01:25:00 PM
Excellent !
Thank you, Kevin !
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tubegeek on December 11, 2019, 12:57:01 AM
Add one more tested 5-knob to the roster. (It's not boxed up yet, but it sounds great!)

Sweeeeeeet unit!

I built mine from Harald's (sabrotone) vero layout with these changes: I put 220R in series with the connection from Q1 collector to pin 1 of the LM13700, and added another connection from Q1 to pin 16 via another 220R. Then I connected 15 to 2, 14 to 3, 13 to 4 and 12 to 5, i.e., I used both OTAs in parallel. I also added .1 ceramics from V+ to V- on each chip - these are not provided on the vero layout. (On the two op amps, the cap fits OK under the IC socket. On the OTA chip, I put the bypass cap on the copper side of the vero.) My Q1 is a 2N3904, reversed with respect to the pinout of the BC327.

Note that, had I noticed that the layout only used one OTA before I started, I could have accomplished the paralleling just by omitting several strip cuts (column 20/rows d, e, f, and g.) I crammed the 220R's in by cutting the crosspieces away from my IC socket - had I done this from the get-go, I could probably have easily fit them underneath with the socket intact. I've attached a couple of post-op pictures of the 16 pin socket, front and back. It would have been MUCH neater to just omit the strip cuts in the first place, of course.

I haven't yet added the yin/yang input clipper LEDs, but I expect to piggyback them between E1 and D1 by soldering them to each other first and then taking only two legs through those holes.

Works great - very clean neutral action, but nothing "dead" or "clinical" about it - really hits the sweet spot. The output level is about 5V pk-pk before clipping which is an awful lot for a guitar pedal! Truly an ace design by merlinb - thank you for sharing this cool effect with us, no wonder it's such a popular build. I'll be drilling a box for this tomorrow!


(https://i.postimg.cc/7Crxvn9T/20191211-004444.jpg) (https://postimg.cc/7Crxvn9T)

(https://i.postimg.cc/LhQ24pvS/20191211-004504.jpg) (https://postimg.cc/LhQ24pvS)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on December 12, 2019, 05:44:26 AM
Truly an ace design by merlinb - thank you for sharing this cool effect with us, no wonder it's such a popular build. I'll be drilling a box for this tomorrow!
Thanks I'm glad you like it! I'll be posting an update to the ET soon which includes a compression indicator and output buffer, plus a minimalist version that only uses 2 opamps.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: tubegeek on December 12, 2019, 06:12:24 AM
Thanks I'm glad you like it!

What's not to like?

Quote
I'll be posting an update to the ET soon which includes a compression indicator and output buffer, plus a minimalist version that only uses 2 opamps.

A maximalist option: taking off from here: https://www.diystompboxes.com/smfforum/index.php?topic=108570.0

I'm looking at a two-band implementation, sort of attempting to fit a Rane DC-24 into a pedal, with fewer (but still a lot of!) options. So far I think it'll look like this: Discrete JFET input buffer, PRR's clever crossover feeding two Threshold controls, an ET behind each Threshold, and an output buffer/virtual earth mixer driving the output.

Crossover discussed here: https://www.diystompboxes.com/smfforum/index.php?topic=112437.msg1037743#msg1037743

I've posted CamH132's drawing here which seems like it was derived from something PRR drew up the thread, now lost due to Tinypic being de-funked. Best I can do for PRR's drawing, is a version I recovered from Google image search in somewhat blurry form, but between the two drawings I think I get the idea:

(https://i.postimg.cc/xJmPx4c7/PRR-crossover-blurry.png) (https://postimg.cc/xJmPx4c7)


(https://i.postimg.cc/2qx388px/Crossover-Splitter-Blend-Updated.jpg) (https://postimg.cc/2qx388px)

A Lot Of Knobs for sure: I'm looking at which controls might best be suited to the nice dual concentric pots Smallbear stocks, which might be a nice way to simplify the front panel. So far I'm pretty sure the two Level pots should be done that way into the virtual earth mixer. And so far I'm pretty sure it DOESN'T make sense to put Attack, Release, and Ratio onto duals. That leaves Threshold as an open question.

Thoughts? Any bass players care to chime in? Jon "midwayfair" P had some excellent input at the topic linked above, but I'm seduced by the neatness of having two OTAs on the LM13700, so I'm loath to build two different compression engines for the two bands.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DaveyJW35 on April 04, 2020, 11:27:00 AM
Here's a picture of my Enginner's Thumb Redux built using a pcb from Jonny Wreckless. I used some beet up pieces of sheet metal, folded EHX style, to give it some mojo.
 
(https://i.postimg.cc/sBZtdj2y/engineer-s-thumb.jpg) (https://postimg.cc/sBZtdj2y)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jhergonz on May 06, 2020, 05:39:32 AM
I just finished reading the whole 32pages of this thread, and I think I never waste even a single second of reading.

thank you Merlin for designing a great circuit, I'am planning to use the ET version 1 for my friend's built in compressor for bass amplifier. I will use both lm13700 in parallel. and will power it with -+15. I hope it will work.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DrAlx on May 17, 2020, 11:18:57 AM
I have built the version 4 circuit using my own layout.
With the level pot at minimum, I hear a weak thump at the output whenever I strum my guitar strings.
I never had that problem with the version 1 circuit.  It was dead quiet with the level at 0.

I think the problem is the output buffer, because if I audio probe directly on the middle pin of the level pot (or on pin 7 of the OTA) it is quiet but pin 8 thumps when I strum.

I am using an LM13600AN instead of an LM13700.  Is the version 4 circuit only suitable for the LM13700 ?
Looking at the datasheet the buffer in the LM13600 seems to be affected by the OTA control current, and I guess that is what is giving the thumps when I strum.

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: slashandburn on May 17, 2020, 05:07:35 PM
I have built the version 4 circuit using my own layout.
With the level pot at minimum, I hear a weak thump at the output whenever I strum my guitar strings.
I never had that problem with the version 1 circuit.  It was dead quiet with the level at 0.

I think the problem is the output buffer, because if I audio probe directly on the middle pin of the level pot (or on pin 7 of the OTA) it is quiet but pin 8 thumps when I strum.

I am using an LM13600AN instead of an LM13700.  Is the version 4 circuit only suitable for the LM13700 ?
Looking at the datasheet the buffer in the LM13600 seems to be affected by the OTA control current, and I guess that is what is giving the thumps when I strum.

I hate to be "that guy". There's probably a logical answer to this but why would you want the output level at 0?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DrAlx on May 17, 2020, 09:29:05 PM
I have built the version 4 circuit using my own layout.
With the level pot at minimum, I hear a weak thump at the output whenever I strum my guitar strings.
I never had that problem with the version 1 circuit.  It was dead quiet with the level at 0.

I think the problem is the output buffer, because if I audio probe directly on the middle pin of the level pot (or on pin 7 of the OTA) it is quiet but pin 8 thumps when I strum.

I am using an LM13600AN instead of an LM13700.  Is the version 4 circuit only suitable for the LM13700 ?
Looking at the datasheet the buffer in the LM13600 seems to be affected by the OTA control current, and I guess that is what is giving the thumps when I strum.

I hate to be "that guy". There's probably a logical answer to this but why would you want the output level at 0?

It's noticeable at low level too regardless of how the ratio pot is set. If you never turn the level down then the noise from the jumps in bias current are buried in the the guitar sound and so you don't notice them.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 18, 2020, 03:02:20 AM
I am using an LM13600AN instead of an LM13700.  Is the version 4 circuit only suitable for the LM13700 ?
Hmm that's could be it, I haven't tested it with an LM13600. Easy enough to eliminate the emitter follower and build it the old way.
(https://i.postimg.cc/CBHLKtmc/5dce939c5feb19088f4ddb56.jpg) (https://postimg.cc/CBHLKtmc)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: DrAlx on May 22, 2020, 09:31:31 AM
Hmm that's could be it, I haven't tested it with an LM13600. Easy enough to eliminate the emitter follower and build it the old way.
My layout was for a PCB so I ordered an LM13700 rather than hack the board.  LM17000 solved the problem.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jubal81 on May 22, 2020, 10:59:39 AM
Any benefit to using a VCA rather than an OTA?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Kevin Mitchell on May 22, 2020, 11:21:05 AM
Any benefit to using a VCA rather than an OTA?
What?

I thought these compressors were an envelope detector controlled VCA.

-KM
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on May 22, 2020, 06:01:29 PM
> using a VCA rather than an OTA?

Is there a difference?

(An OTA is a building-block often used with other parts to make a VCA.)

(Randomly changing one to the other will force other changes throughout.)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on May 25, 2020, 03:29:06 AM
Any benefit to using a VCA rather than an OTA?

(https://i.postimg.cc/tZ9RzTT8/price.jpg) (https://postimg.cc/tZ9RzTT8)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Ben N on May 25, 2020, 06:02:32 AM
Any benefit to using a VCA rather than an OTA?

(https://i.postimg.cc/tZ9RzTT8/price.jpg) (https://postimg.cc/tZ9RzTT8)
Amen! Preach it!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Sanguinicus on June 08, 2020, 06:20:01 AM
Been wanting to build this thing for ages. Finally did. But it's got a problem.

I've built the two-knob version for now. The level knob works as expected, max is basically unity volume (is that correct?).
The problem is with Ratio. Fully counter-clockwise (or fully clockwise, i get the pot pins mixed up) it basically sounds like the bypassed signal. Turn it up slightly and it goes through a very brief staticky/scratchy transition... to basically the same thing. Now with a bit of noise in the signal and possibly kind of, sort of compressed, there's slight background noise too. The rest of the sweep does nothing to affect the signal.

Treble boost doesn't seem to work either, could be unrelated. But I'm not fussed with getting that working at the moment.

Anything obvious I should check? I've done the whole remeasuring, reflowing, etc apart from voltages. I'm using the Tagboard Effects vero layout with CA3080 (known working, used it in a previous comp). I really want to get this working.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 09, 2020, 06:42:50 AM
Anything obvious I should check? I've done the whole remeasuring, reflowing, etc apart from voltages. I'm using the Tagboard Effects vero layout with CA3080 (known working, used it in a previous comp). I really want to get this working.
Post your voltages, and a link to the layout you used.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Sanguinicus on June 09, 2020, 06:46:12 AM
Anything obvious I should check? I've done the whole remeasuring, reflowing, etc apart from voltages. I'm using the Tagboard Effects vero layout with CA3080 (known working, used it in a previous comp). I really want to get this working.
Post your voltages, and a link to the layout you used.

is there a reference of what the voltages should be? So I can check as I go.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 09, 2020, 06:54:04 AM
is there a reference of what the voltages should be? So I can check as I go.
For the layout you're using, I don't know, maybe you can contact whoever made it. People swap the opamp sections to suit their needs, and the CA3080 is another deviation from the stock circuit. There is no universal "this pin should always be X" formula. If there is a schematic to go with the layout you're using then it would be ideal if you wrote the voltages directly on it. Then we will probably be able to see at a glance what it wrong.
The voltage chart for my Iss.3 version may help: http://valvewizard.co.uk/engineersthumb3.pdf
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Sanguinicus on June 09, 2020, 07:15:12 AM
Hit this link for my voltages.

https://www.dropbox.com/s/adqnkn3yy2q888s/ET%20voltages.png?dl=0

Should have mentioned the Q also. C=4.5, B=2.5, E=4.0

All these are obviously effect engaged. No signal, just guitar plugged in. Needed to hold the dmm probes.

Vero build here:
https://tagboardeffects.blogspot.com/2012/11/engineers-thumb.html
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 09, 2020, 07:34:11 AM
Should have mentioned the Q also. C=4.5, B=2.5, E=4.0
Something funny going on with the transistor and pin-5 of the CA3080. Collector & pin-5 should be around 0.6V, not 4.5V.  Also, you said B = 2.5V, but on the diagram you posted you've written IC2 pin-1 = 3.7V? They should be the same since they're connected together.
Looks like the problem in in that area, so check your connections there. Almost looks like C & pin-5 are not connected together, or the transistor is the wrong type / wrong way around / bad.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Sanguinicus on June 09, 2020, 07:42:47 AM
Yeah I just found an error on my board. Now I fixed that but now it sounds like an overdrive. The Ratio control increases gain and volume. Level works as per normal, still no noticeable treble control.

It's a pretty sweet overdrive to be honest, But I came here for compression!

EDIT: After doing extra reading, I found that by even measuring the bias input (pin 5) of the OTA, you can fry it. So perhaps this is what happened and why it's sounding like an overdrive. Time to hunt for a new one, or a LM13700 i think.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: changes on June 12, 2020, 06:30:55 AM
Hello

I've built this LED indicator mod and works pretty good but I am interested in the opposite indication. Dark when compressing... Any help is more than welcome


> the ouput of that opamp to B of a NPN. Simple enough.

That won't work. The LED is always-on and carrying infinite current. Also fouls-up the compressor.

There's a simple linear-proportional way to add an indicator. See the BC327 PNP and 1K resistor? This flows a current proportional to over-level, and closely related to amount of gain reduction. That current is weak and already committed to tickling the LM13700. But we can take the same Base signal, to a second PNP, with a smaller resistor, and get a proportionally larger current we can dump to an LED.

(This form of "current mirror" has a small 40mV mirror-error which is totally moot for a visual indicator.)

(http://i.imgur.com/IXLn0BP.gif)

The light happens when the compressor is "doing something", which makes sense to me. If the LED is off, it is just a buffer/booster. When signal gets loud, so that the sidechain tickles the '13700 to turn-down the signal, the LED turns-on and gets brighter.

For bench-test only, you can put your volt-meter *across* that 1K resistor. Use a 2V range (auto-ranging may be confused by dynamic guitar signals). The DC voltage is zero for no- or small-signal. When signal is excessive, voltage will increase to 1V (maybe a bit more or less), fading back to zero as the note decays.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 12, 2020, 08:21:14 PM
> Dark when compressing...

Dark-emitting diode.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: changes on June 13, 2020, 05:17:13 AM
 :D :) :) :D :) :) :D

Wish there was one.


> Dark when compressing...

Dark-emitting diode.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 13, 2020, 09:05:53 PM
(https://i.postimg.cc/yg8C8CjS/Dimwhencompressing-42.gif) (https://postimg.cc/yg8C8CjS)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 15, 2020, 06:35:13 AM

I've built this LED indicator mod and works pretty good but I am interested in the opposite indication. Dark when compressing... Any help is more than welcome
This *might* work if you play with the resistor value, but LEDs don't vary their brightness in a convenient way so it might not be possible to get a useful variation in brightness with signal level. Easy enough to try though. Try 1k to 2k to start with.
(https://i.postimg.cc/dZD8td6s/fireplace.jpg) (https://postimg.cc/dZD8td6s)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: changes on June 15, 2020, 12:41:18 PM

I've built this LED indicator mod and works pretty good but I am interested in the opposite indication. Dark when compressing... Any help is more than welcome
This *might* work if you play with the resistor value, but LEDs don't vary their brightness in a convenient way so it might not be possible to get a useful variation in brightness with signal level. Easy enough to try though. Try 1k to 2k to start with.
(https://i.postimg.cc/dZD8td6s/fireplace.jpg) (https://postimg.cc/dZD8td6s)

(https://i.postimg.cc/yg8C8CjS/Dimwhencompressing-42.gif) (https://postimg.cc/yg8C8CjS)


Thanks guys

I'll try both asap and get back with the results

Cheers
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on June 16, 2020, 04:34:44 AM
I've recently had a few people message me about PCBs for the "Engineer's thumb redux" I did a couple of years ago. This was based on the ET with JFET input and the inclusion of a noise gate into the compressor. I don't have any boards left, but you can find the Gerbers and NC drill files for the board I made, along with the schematic and bill of materials in my shared Google drive folder:
https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing (https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing)
Feel free to make some more boards from these Gerbers if you like.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on June 16, 2020, 06:22:14 AM
Hi Merlin, I'm referring to your issue 4, where you use LM13700's buffer for output. Would paralleling those transistors give less noise? Like this, for example:

(https://i.postimg.cc/hhbBvzDx/lm13700.jpg) (https://postimg.cc/hhbBvzDx)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on June 16, 2020, 08:30:43 AM
Hi Merlin, I'm referring to your issue 4, where you use LM13700's buffer for output. Would paralleling those transistors give less noise? Like this, for example:
I doubt it would make the slightest difference since most of the noise comes from the OTA itself, but you can try. I'm not sure how well matched they'll be; they're on the same die but they're also Darlingtons. I don't think it will hurt anything though.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on June 16, 2020, 06:54:18 PM
If a competent designer (say, Merlin) put an emitter follower *after* a volume control, then noise should be a non-issue.

I don't see how it would help or hurt, or be worth the effort to change an existing PCB/layout.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rutgerv on July 12, 2020, 03:15:12 PM
After working my way through the wonderful pages of this thread, I feel enthusiastic about building my own ET. I have plans to build it into a guitar box that I plan to use for silent guitar recording. I designed a variable impedance buffer (just for the heck of it), some tone controls (bright switch, mid scoop, high-pass and low-pass filters + wah), and was considering a JFET based pre-amp circuit before going into either (a) my computer or (b) a stand-alone power-amp + cab simulator.

I was planning to put a compressor before the pre-amp. Because I come from designing synths I have pile of modern SSI2164 VCA's, which I use for the tone control section and wah as well. I was wondering if it would be worthwhile (in terms of THD+N performance) to redesign the ET for using this part (instead of the LM13700). What do you think?

I recall from the datasheet that 2164's have their best performance around unity gain, which means the 'OTA inside feedback-loop' design is probably no longer needed. Also, 2164's can be paralleled to achieve even better performance (if needed). One drawback: the control law of input of the 2164 is not linear (like the LM13700) but logarithmic, so the current detector+envelope circuit can't be connected directly. One way to overcome this is to use a second section of the 2164's to linearise the first section? Or would there be alternative detector+envelope approaches that put out a dB-linear control signal?

Regards,

Rutger
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jhsa on July 25, 2020, 08:28:19 PM
I finished my latest batch of changes to the gate design. I added a new peak detector, and a threshold comparator with some hysteresis. I also added separate attack and release controls for the noise gate. It's now an 8 knob monster :icon_cool:

Here is the schematic:
(https://s33.postimg.cc/r3x63rxyz/Capture.png) (https://postimg.cc/image/r3x63rxyz/)

Here are some photos of the revision C PCB:
(https://s33.postimg.cc/rhyi2tcrf/IMG_20180620_152517747.jpg) (https://postimg.cc/image/rhyi2tcrf/)
(https://s33.postimg.cc/nll66tzhn/IMG_20180620_152533863.jpg) (https://postimg.cc/image/nll66tzhn/)
(https://s33.postimg.cc/bz125vc8b/pcb.png) (https://postimg.cc/image/bz125vc8b/)


Here it is in action. Sorry for the poor audio quality, it's just my phone camera, which is adding some weird compression of its own to the sound :(
One day I'll get a proper camera and mic for this stuff.


Overall I am fairly happy with the circuit design. It's a bit more complex than I would have liked, and at 100 x 70mm will no longer fit inside a 1590B (you need a 1590BB instead), but the added flexibility to the noise gate is nice. Let me know if you would like a PCB to build yourself.
I know it's been a while since this was posted :)
Someone just pointed this version to me. I did build the original ET with all flavors and I love it, but I am probably going to give this one a try as well :) I have had a quick look at the schematic and noticed a couple things. No input or output caps. Normally pop sounds when switching are caused by DC. Caps will block DC.
Also connect pin 1 of the MAX1044 to pin 8 to increase the operating frequency to something well above the audio spectrum. If using the ICL7660 instead, which is what I have, use the 7660S and also connect pin 1 to pin 8. I believe you could then even remove TR3 and it would still be silent :)
Can't wait to give this a try.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: dbarrie on July 30, 2020, 02:43:56 AM
So I've built up merlinb's version 2 (http://valvewizard.co.uk/engineersthumb2.html) of ET with the modifications mentioned to make it suitable for bass (namely, the 220k release resistor and 2.2uF caps on the input to opamp C) on a breadboard, but as a few other people mentioned in this thread, I'm getting some awful distortion when using the compressed signal. All the voltages I've measured seem reasonably close to what others have shown is correct.

Some details about the build and what I've done so far to debug it:

The build is sitting on a breadboard right now. I've got it laid out pretty clean, with the component leads cut short and hook-up wire connecting things that need it. Obviously a breadboard is going to cause some issues, but the amount of distortion I'm hearing seems like way more than can be attributed to the stray capacitance of the breadboard! I've got the pots and jacks hooked up using additional lengths of hook-up wire. The circuit is powered by a 9V wall-wart that measures at 9.22V. I didn't have any TL072s or TL074s on hand when putting it together, so I've used 3 TL071s as the A, B, and C opamps, and an LM358 to generate the 4.5V rail. I've not connected any of the offset pins of the TL071s - they're just floating. I'm also using an LM13700.

My bass has an on-board EQ (made of 3 TL072s, bass/mid/treble). I get an output of ~100mVpp with it disabled, and ~200mVpp with it enabled and zeroed out.

When probing the circuit, I see the base of the transistor oscillating between ~4.2 and ~4.75V at 60Hz, obviously picking up some hum from the computer, monitors, power supply, etc. When playing the bass, I do see it immediately turn into a very narrow pulse and then split into two (one smaller than the other) as the signal dies down. Adjusting the attack pot changes the way this behaves, and it feels like that part is doing something that seems maybe correct, if you'll pardon my inability to describe it very well. If anyone can describe what that signal should look like, I'd love to be able to compare it to what I'm seeing.

The compression part does definitely appear to be working. When I let a note ring out, I hear it start out loud and quickly get compressed as the attack kicks in, followed by it being amplified to around the same level where it would normally start fading away. Changing the attack knob can give me a bit of a pulsing or "wooshing" effect. It just sounds really, really distorted and bad!

Is there anything obvious I should try? Is that 60Hz noise on the transistor's base the likely culprit here? What should that signal look like when not playing? Are there other points I should try probing?

I can post oscilloscope screenshots if people would find them useful!
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on July 30, 2020, 02:57:45 AM
I know it's been a while since this was posted :)
Someone just pointed this version to me. I did build the original ET with all flavors and I love it, but I am probably going to give this one a try as well :) I have had a quick look at the schematic and noticed a couple things. No input or output caps. Normally pop sounds when switching are caused by DC. Caps will block DC.
Also connect pin 1 of the MAX1044 to pin 8 to increase the operating frequency to something well above the audio spectrum. If using the ICL7660 instead, which is what I have, use the 7660S and also connect pin 1 to pin 8. I believe you could then even remove TR3 and it would still be silent :)
Can't wait to give this a try.
Let me know if you want me to share the Gerbers or NC drill file for the 8 knob redux version.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: Rob Strand on August 02, 2020, 11:02:23 PM
Quote
Let me know if you want me to share the Gerbers or NC drill file for the 8 knob redux version.
I like your London bridge PCB holder.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on August 04, 2020, 12:34:40 AM
I like your London bridge PCB holder.
https://www.amazon.com/Aven-17010-Adjustable-Circuit-Holder/dp/B00Q2TTQEE/ref=sr_1_2?dchild=1&keywords=circuit+board+holder&qid=1596515622&sr=8-2 (https://www.amazon.com/Aven-17010-Adjustable-Circuit-Holder/dp/B00Q2TTQEE/ref=sr_1_2?dchild=1&keywords=circuit+board+holder&qid=1596515622&sr=8-2)
This was bought for the purpose unlike my cable organizer which is a hat rack :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: merlinb on August 05, 2020, 02:54:42 AM
Quote
Let me know if you want me to share the Gerbers or NC drill file for the 8 knob redux version.
I like your London bridge PCB holder.
Tower bridge ;)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: 11-90-an on August 07, 2020, 07:43:12 AM

Here is the schematic:
(https://s33.postimg.cc/r3x63rxyz/Capture.png) (https://postimg.cc/image/r3x63rxyz/)


If there was a quota for questions asked per day i think i blew it by now... :icon_mrgreen:

Here goes...

Why is there no DC blocking cap in the buffer input stage? And could the JFET buffer be replaced with a BJT buffer?

And also, is there a specific reason why the 1uFs and 10uFs are ceramic here? Would there be a drastic difference with electrolytics?

Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rankot on August 08, 2020, 04:20:52 AM
Why is there no DC blocking cap in the buffer input stage? And could the JFET buffer be replaced with a BJT buffer?
Because there are caps later in signal chain which will stop DC passing further.

And also, is there a specific reason why the 1uFs and 10uFs are ceramic here? Would there be a drastic difference with electrolytics?
1u shall be polymer caps, not ceramic, as they're much better sounding compared to elco.
10u caps are in switching module, so using ceramic will have lower ESR and smaller footprint.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on August 08, 2020, 05:14:31 AM
As Ranko said, you get less losses and better HF performance by using film and multilayer ceramic caps rather than electrolytics. They've gotten a lot cheaper in the last few years so you might as well use ceramic for 10uF, and electrolytic for bigger values say 47uF upwards. Also in some circuits you want to block DC. Electrolytics don't like having zero bias across them or being reverse biased, it messes with the chemistry of the electrolyte; you don't need to worry about that with ceramics so they make better DC blocking caps for audio circuits generally.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on August 08, 2020, 02:04:16 PM
> Why is there no DC blocking cap in the buffer input stage?

What DC bias voltage is needed at this JFET's Gate?

> And could the JFET buffer be replaced with a BJT buffer?

What DC bias voltage is needed at this BJT's Base?
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on August 14, 2020, 05:36:54 PM
Let me know if you want me to share the Gerbers or NC drill file for the 8 knob redux version.

Definitely! Only thing, I am planning to make it as a rack unit, so... I guess, I won't need 7660 :) But this is something, I can handle myself. Sadly, not true for good PCB layout :)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on August 15, 2020, 07:21:01 PM
Let me know if you want me to share the Gerbers or NC drill file for the 8 knob redux version.
Definitely! Only thing, I am planning to make it as a rack unit, so... I guess, I won't need 7660 :) But this is something, I can handle myself. Sadly, not true for good PCB layout :)
Here you go:
https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing (https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 03, 2020, 06:37:27 AM
Here you go:
https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing (https://drive.google.com/drive/folders/1usNiADluT3tfycfkl7Y7Yo24fzZkVLZN?usp=sharing)

Thank's a lot! Also - brilliant work on the noise gate. This is something I am currently planning to tinker around. So far, I've came up with idea to level shift gate's control voltage from current implementation and then use it to control the THAT2180 VCA. Only problem here is, that I need a reference voltage to be set using a trimmer (VR4) on schematic. Maybe someone has better ideas? )

(https://i.postimg.cc/v1VMvP7f/NG.png) (https://postimg.cc/v1VMvP7f)
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rutgerv on September 04, 2020, 01:03:52 PM
Hi kgusarov,

Interesting indeed! I'm actually in the process of transforming the ET to work with an SSI2164 VCA. In many ways this vca is similar to the that2180. Keep in mind that the original ET uses a LM13700 with lineair control law, while the abovementioned VCA's are expotential in their response to the control signal. For gating the control law may not be so important, but for compression it is. I'm using a second VCA inside the loop of an opamp to transform the ET's lineair control signal into what the expo VCA likes to receive. Will post with progress update soon.

Rutger

Rutger
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 04, 2020, 03:29:16 PM
I'm actually in the process of transforming the ET to work with an SSI2164 VCA.

Well, AFAIK, Analog Devices mark this as obsolete, and I don't trust any other manufacturers (this is my thing of trusting official ones only). So, I'd stick with THAT.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 04, 2020, 04:09:25 PM
> Analog Devices mark this as obsolete

That's the SSM parts. Rutger is saying SSI. Same function under yet another company. I remember these parts from the 1980s. They go in and out production here and there.

Dan Parks is CEO of SSM and former Audio Products Director at Analog Devices and National Semiconductor.
https://audioxpress.com/news/sound-semiconductor-expands-ic-range-with-new-single-and-dual-vca-chips
https://www.soundonsound.com/news/sound-semiconductor-release-huge-quad-vca-data-sheet
https://en.wikipedia.org/wiki/CEM_and_SSM_chips_in_synthesizers
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 04, 2020, 04:23:57 PM
Same function under yet another company.

Still, this is my thing :) You can call me snob, but I trust TI, Analog and other big companies. I know, others do good things, but this is why I buy Samsung instead of Xiaomi :) Way of living, I guess ) Also, I buy from Mouser/Farnell due to my living place... And haven't seen small brands there...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: PRR on September 04, 2020, 04:48:36 PM
SSI is a fully kosher company with roots in this technology.

Yes, it is a >teeny< company with products that went "obsolete" (insufficient demand) at 2 or 3 other companies already.

And they only sell through a few distributors, also small shops not Mouser/Farnell. I'm sure there are places and people who just should not try to buy SSI.

Much depends on your production. For a solo guitarist with good delivery service, you can just buy a 10-pack which will be a lifetime supply. (What I did when the LM377 chip was shut-down: I bought a handful and they lasted until I left that place and quit abusing that amplifier.) If you are starting a factory and signing with Banjo-World to supply a million ETs a year, you want to avoid a small unsure supplier (or else buy them as a pet).
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 04, 2020, 04:59:22 PM
And they only sell through a few distributors, also small shops not Mouser/Farnell

This already goes to the offtopic :) But haven't found any trusty place in EU...

To stay more focused on the topic itself... I was also thinking on using JFET, but that seems easier to me so far. Since I can provide kind of reference voltage to EC+/EC- and scale the gate CV so, it will definitely be closed. When EC+ = EC- gain is 0db, which is great point for gate openning. Only problem atm for me is that I am out of ideas on how to generate stable VREF without need for a precision trimmer and millivoltmeter...
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: rutgerv on September 05, 2020, 04:27:54 AM
I usually use the Lm4040 for reference voltages.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 05, 2020, 04:33:57 AM
I usually use the Lm4040 for reference voltages.

I usually prefer LT1009 or TL431. However, it still would require a lot of tuning with high precision instruments due to high sensitivity of THAT IC. Even slight difference will cause the signal to be boosted/attenuated. On the other hand, it should be possible to use JFET still, I guess, or even put LM13700 in signal path for "coloring".
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: jonny.reckless on September 08, 2020, 03:09:25 AM
If you're using a THAT VCA I recommend one of their excellent application note designs as a starting point. I've built a couple and they are studio quality and sound fabulous on a wide variety of program material. It's important to get the power supplies, grounding and impedances right to get the best low noise low distortion performance out of those chips. In particular the control port needs to be driven with a low impedance, low noise, low distortion amplifier. You don't want any TL072s anywhere near it.

http://www.thatcorp.com/datashts/dn01A.pdf (http://www.thatcorp.com/datashts/dn01A.pdf)
http://www.thatcorp.com/datashts/dn00A.pdf (http://www.thatcorp.com/datashts/dn00A.pdf)
http://www.thatcorp.com/datashts/dn107.pdf (http://www.thatcorp.com/datashts/dn107.pdf)
http://www.thatcorp.com/datashts/THAT_4305_Datasheet.pdf (http://www.thatcorp.com/datashts/THAT_4305_Datasheet.pdf)

The engineer's thumb is a completely different beast and I fear trying to combine it with a THAT VCA you will end up with an expensive mule, i.e. neither one thing nor the other, since the CCA sidechain law is linear in the ET and exponential in the THAT for a start.  The ET is a great low cost simple compressor which excels for what it was designed.
Title: Re: THE ENGINEER'S THUMB... At last, a better compressor!
Post by: kgusarov on September 08, 2020, 03:17:50 AM
I agree, that it will be step away, but it is always nice to do some experimentation. TL072's are there due to the fact, that they ended up faster to simulate in LTSpice, than other opamps :) So, I put them in every design, since they converge so good. I was basically thinking of turning this into 2-stage thing - first gate, then compressor, otherwise it seems, that compression ratio also affects gate response.