Was seatching for diy octave down sound demos and found this guy who made a really simple compressor... no I/O caps, though, but I guess that was part of the "simplest" concept...
He put some build docs In his description...
I can't wrap my mind around it, though, as most of the circuitry and jacks use ... virtual ground?
It is quite interesting though...
Seems like the attack would be instantaneous. Just needs a little makeup gain stage. Very cool.
Interesting... Needs a couple more components, but it certainly IS simple! And it works! (would not trade it for my Engineer's Thumb, but it does work!)
QuoteI can't wrap my mind around it, though, as most of the circuitry and jacks use ... virtual ground?
Just think of the ground connection between the input and output being ground.
After that the supply is non-grounded.
To me it's like balancing a broom on the end of the handle. You need to finely and manually adjust the DC bias on the MOSFET to put it in a workable zone. The sharp MOSFET characteristic provides the knee. It's kind of half-wave rectifiying but kind of worse because on one signal polarity it turns off the MOSFET more.
The long time constant of the lamp will slow things down and hides a lot of distortion.
Quote from: Rob Strand on October 17, 2020, 09:55:17 PM
QuoteI can’t wrap my mind around it, though, as most of the circuitry and jacks use ... virtual ground?
Just think of the ground connection between the input and output being ground.
After that the supply is non-grounded.
So the ground are connected via the 10k resistor?
I redrew the schem a bit to help me understand...
(https://i.postimg.cc/mtCrW4g3/image.jpg) (https://postimg.cc/mtCrW4g3)
Did I reverse anything accidentally? :icon_redface:
I’m thinking there’s a chance that the MOSFET can be replaced with a BJT, and we could add some I/O caps... maybe a resistor from MOSFET to bulb and a cap from the resistor to ground for a attack/release/decay/whatever-it’s-called control? Probably also a simple LPB-1 boost after?
I think I’m getting overexcited... :icon_lol:
QuoteSo the ground are connected via the 10k resistor?
No, the grounds connect together, then the input and output (the center pins) connect together via the 10k. The output LDR forms a divider with the 10k and reduces the output level.
Quote from: Rob Strand on October 17, 2020, 11:35:50 PM
QuoteSo the ground are connected via the 10k resistor?
No, the grounds connect together, then the input and output (the center pins) connect together via the 10k. The output LDR forms a divider with the 10k and reduces the output level
So I've been drawing schems wrong the entire time... :icon_redface:
Wait... the how does the MOSFET get triggered now since it's gate is basically tied to ground?
QuoteWait... the how does the MOSFET get triggered now since it's gate is basically tied to ground?
The audio input drives the source!!! and the gate is grounded.
The current through the lamp passes through the battery and MOSFET but that lamp drive circuit and audio circuit only touch at one point, the source. It's like two separate circuits.
The pot biases the MOSFET right at the point where the MOSFET is turning on so a small amount of audio signal pushes past that point and the lamp turns on. So the audio signal connects to the MOSFET at two points the gate and the source.
Yeah its pretty weird but you can have things like that when you have floating circuits (here the PSU) and high-impedances (here the gate and source). If you don't want to go crazy you have to separate the parts of the circuit in your mind.
So I'm guessing this pedal wouldn't work with a daisy-chained PSU? Since I/O jack ground will be connected to PSU ground because of possible other pedals?
QuoteSo I'm guessing this pedal wouldn't work with a daisy-chained PSU?
Not as is.
However, if you add some caps to give DC isolation it's possible to juggle things around so the different parts of the circuit have the same ground. Roughly like this,
100k pot drawn as 2x50k's:
(https://i.postimg.cc/5YzcgRHm/Dodgy-Comp-V2-0-2020-10-19.png) (https://postimg.cc/5YzcgRHm)
Quote from: Rob Strand on October 18, 2020, 09:08:08 PM
QuoteSo I'm guessing this pedal wouldn't work with a daisy-chained PSU?
Not as is.
However, if you add some caps to give DC isolation it's possible to juggle things around so the different parts of the circuit have the same ground. Roughly like this,
100k pot drawn as 2x50k's:
(https://i.postimg.cc/5YzcgRHm/Dodgy-Comp-V2-0-2020-10-19.png) (https://postimg.cc/5YzcgRHm)
Now that you drew it, it *finally* makes sense... thanks, Rob... :icon_biggrin:
I'll try to find a way to pull this off with a BJT... :icon_biggrin:
QuoteNow that you drew it, it *finally* makes sense... thanks, Rob... :icon_biggrin:
I'll try to find a way to pull this off with a BJT... :icon_biggrin:
With the BJT you lose the high impedance into the gate. Since you already have power you could add a buffer but the on/off threshold probably sharper with a BJT compared to a MOSFET. See how you go. The MOSFET version is "rough and ready" anyway.
Worked on it the whole day, and here's what I came up with:
(https://i.postimg.cc/y30FHjKj/IMG-3563.jpg) (https://postimg.cc/y30FHjKj)
It's a nifty little compressor (or should I say,
limiter) and squishes nicely...
Transistors can be any generic type, I used BC547s
So I'm just gonna break it down a bit... but I'm afraid I can't explain much at all... :icon_redface:
1. Input buffer - Rob suggested that there should be a buffer up front, so I did that. First I started with a Sziklai pair, but then it used 2 trannies, and it wouldn't be that simple anymore, right? So I chucked out the PNP and it works... :icon_lol:
2. Crude Envelope follower (More like signal bleeper, but oh well...) - 100k trimpot biases the transistor that the LED would be slightly on, and with one big strum, should make the LED light up to it's brightest, (limited by the CLR, of course) then go back down to a slightly on state... honestly I can't explain, but the watching the video from the start of the thread should clear some stuff up... ::)
Quote
I used a blue LED, but it's only because it was the nearest LED to my hand at the time. Other colors will also have different respones.
I also used 10k as the CLR value, but that was simply because 10k seemed to be the safest value of that LED... of course, different LEDs need different CLRs..
3. Boost - Basically the beavis colorboost with a higher input resistor because of some fizz I noticed...
(https://i.postimg.cc/kDzmhdTq/Beavis-Colorboost.gif) (https://postimg.cc/kDzmhdTq)
From the output of that 1u cap, the 10k controls the amount of compression (or depth of compression). I used 2 LDRs because I wanted a quicker and sharper response from it...
And the 100k pot is a volume pot since the boost can give lots of gain. I think around 10 o'clock would be unity signal...
Overall, I'm quite happy with this circuit, simple and works well, of course doesn't compare to a dynacomp or engineer's thumb, I recommend you break out the great and finicky breadboard that you have sitting in the corner and try it out. I wanna see if it works out for others too... also, please, suggestions and corrections are appreciated a lot.. :icon_biggrin: It's still on breadboard, after all... :icon_mrgreen:
p.s.1. When sustaining, say, a chord or low note, that was strummed hard, there is a tendency of envelope ripple. Placing the 1u cap from LED cathode to ground helped a bit, but putting a traditional RC network before the transistor doesn't really work, it upsets the balance of the envelope follower I guess...
p.s.2. I don't recommend rolling a vactrol, but placing them right beside each other with the LDR facing the LED it better, without rolling, so you can see the LED blinkity blinking, as looking at the LED makes tweaking the trimpot much easier.
p.s.3 There seems to still be some fizz in the decay of hard-strummed notes... anybody with an idea to remove this?
I haven't gone through all the details of your post yet - have to go do something.
QuoteWorked on it the whole day, and here's what I came up with:
Very keen!
QuoteThere seems to still be some fizz in the decay of hard-strummed notes... anybody with an idea to remove this?
It might be the transistor driving the LEDs. When the signal is positive a large current flows into the base because the BE junction to act like clipping diode. You might be able to put a resistor in series with the 1uF cap on the base, try 2k2. A smaller cap might also help but the resistor is better.
Made some revisions... now it's in version 1.1
(https://i.postimg.cc/K32c6c1V/IMG-3565.jpg) (https://postimg.cc/K32c6c1V)
- Corrected some wrongly written values, 5.1M -> 5.6M
- Component value changes, 470k ->220k, 10k pot -> 5k pot
- Added 2.2k resistor in series with 1u cap to reduce fizz from envfollower (Thanks Rob, fixed the problem entirely... ;D)
I still need a name for it though, any suggestions?
I think I'll just call it Optical Limiter or "OptoLim"... :icon_cool:
I made a perf layout, could you guys spot any mistakes/errors? Any perfing rules broken? :icon_lol:
I'm basing it off the v1.1 schem ^^
(https://i.postimg.cc/v4SyQmtP/Screen-Shot-2020-10-20-at-5-08-32-PM.png) (https://postimg.cc/v4SyQmtP)
Nice :)
Thank you for the layout, and the schematic!
Any plan to release a veroboard layout as well at some point?
Quote from: snk on October 20, 2020, 06:11:49 AM
Nice :)
Thank you for the layout, and the schematic!
Any plan to release a veroboard layout as well at some point?
Thanks! The layout isn't verified yet, when I get my trimpots I'll try it. never worked with vero before, but I'll give it try... :icon_mrgreen:
nifty lil comp/lim.....why 2 ldrs?
Quote from: deadastronaut on October 20, 2020, 06:42:35 AM
nifty lil comp/lim.....why 2 ldrs?
I also wanted a steeper and faster volume deduction, since they're wired in parallel, the volume will go down x2 as fast than with only 1 LDR
Also, forgot to add. Don't use ready made vactrols as they're probably too fast... :icon_lol:
The best LED's to use are the slow ones. Less ripple.
OptoLim v1.1
(https://i.postimg.cc/4Kbp2Y62/IMG-3588.jpg) (https://postimg.cc/4Kbp2Y62)
- Corrected some wrongly written values, 5.1M -> 5.6M
- Component value changes, 470k ->220k, 10k pot -> 5k pot
- Added 2.2k resistor in series with 1u cap to reduce fizz from envfollower
UNVERIFIED perf layout:
(https://i.postimg.cc/TKsBD02V/Opto-Lim-v1-1-perf.png) (https://postimg.cc/TKsBD02V)
UNVERIFIED vero layout: (my first vero, so there might be tons of mistakes... keep alert! :icon_lol:)
(https://i.postimg.cc/rKRT1xcT/Opto-Lim-v1-1-vero.png) (https://postimg.cc/rKRT1xcT)
Wow, that was fast!
Thank you, 11-90-an !
I have other projects to finish first, but this one goes on top of the "todo soon" pile :icon_mrgreen:
Is it suitable for bass instruments (I am no guitar player)?
when you say slow LEDS are best .........
write the revision number on the drawn circuit each time, so's we don't confuse. and nice work.
(https://i.postimg.cc/K32c6c1V/IMG-3565.jpg)
Quote from: snk on October 20, 2020, 10:07:56 AM
Wow, that was fast!
Thank you, 11-90-an !
I have other projects to finish first, but this one goes on top of the "todo soon" pile :icon_mrgreen:
Is it suitable for bass instruments (I am no guitar player)?
Thanks! I discovered that making layouts is fun and since today is a holiday for me, I decided to do it now. Of course, it's not verified, so build at your own risk...! :icon_mrgreen:
I don't have a bass, but I think it will do fine if your increase the all the 1uF caps to say, 2.2uF, except for the one beside the LED... but if you do you would probably have to increase the 2.2k beside the LDR (in the vero layout) to maybe 3.3k... It would do fine with the standard 1uF's...
Quote from: duck_arse on October 20, 2020, 10:20:43 AM
when you say slow LEDS are best .........
write the revision number on the drawn circuit each time, so's we don't confuse. and nice work.
(https://i.postimg.cc/K32c6c1V/IMG-3565.jpg)
Good point... forgot to do that, sorry... :icon_redface:
And thanks too.. :icon_lol:
EDIT:
Updated it, and it has quite the trash resolution, since there is a lack of light and it's nighttime already. I'll retake tomorrow morning. :icon_biggrin:
If your TRIM pot is turned all the way, you have full supply voltage through the transistor base, which will burn it.
You clearly never need more than 0.7V here, if that.
Quote from: PRR on October 20, 2020, 12:48:28 PM
If your TRIM pot is turned all the way, you have full supply voltage through the transistor base, which will burn it.
You clearly never need more than 0.7V here, if that.
Yep. I need to write more detailed instructions... :icon_redface: I'll update them later.
EDIT: layouts updated with more instructions
do you trust people taht much? PRR would want you to fit stop resistors so the burn can't happen, I'm sure. he might not care, but still.
Quote from: duck_arse on October 21, 2020, 09:32:16 AM
do you trust people taht much? PRR would want you to fit stop resistors so the burn can't happen, I'm sure. he might not care, but still.
I *actually* tried it when I was BB'ing... no magic smoke... :icon_eek:
My excuse would now be "lack of space" but I digress...
nuh-uhh, youse gots no excuse - I can see a dozen empty holes on your perf [if I'm looking the right one], you only need one resistor added. and speaking of wrong - where does the 9V connect to on the perf, just that empty pad?
Quote from: PRR on October 20, 2020, 12:48:28 PM
If your TRIM pot is turned all the way, you have full supply voltage through the transistor base, which will burn it.
You clearly never need more than 0.7V here, if that.
What's wrong with relying on some healthy control on one's actions? :D
The bias trimmer is not only dangerous, as Paul pointed out, it is also unnecessary. Replace it with a 220k or so Resistor from base to supply in plus two antiparallel silicon diodes from base to ground. That way the transistor will idle at the brink of turning on, which seems to be what you want. I personally would leave the diode that points down (cathode to ground) and the resistor to supply out completely, to get a threshold of 0.7V. The diode that points up should be there to protect the base from going too far below the emitter. In that case, also add a resistor from base to ground. 220k should work.
EDIT: Have a look at the envelope detector of the MXR Dyna comp for comparison: https://www.electrosmash.com/mxr-dyna-comp-analysis
You can get away with this static bias because you are using a BJT. BJTs have a very predictable turn on voltage of about one silicon diode drop between base and emitter. The original youtube circuit used a MOSFET. Now these things definitely need a trimmer because their turn on voltage is quite variable, so you never know if any individual MOSFET will turn on at 0.5V or at 1.9V or whatever.
Andy
QuoteThe bias trimmer is not only dangerous, as Paul pointed out, it is also unnecessary.
Naw, there is a reason of the trimpot. The transistor needs to turn "almost on", yes, but each LED has a different color, and brightness/CLR . In other words, each time you swap out an LED, the bias would have to be re-tweaked. Tried and tested. :icon_lol:
Quotewhere does the 9V connect to on the perf, just that empty pad?
Fixed that. I'm making v1.2 layout since there are much needed (like Paul's warning) and slightly needed (fizz reduction) improvements...
Why would you swap out the LED? CLR definitely needs to be adjusted to suit the LED you are using. This will control the brightness and therefore the sensitivity. Why not replace CLR with a resistor + pot in series and loose the 5k pot at the LDRs? That way you have a sensitivity control that also takes care of adapting the circuit to the LED you are using.
Andy
I tried it, and I think I know why it isn't working... (your reversed diode and resistor configuration)
The dynacomp is a feedback compressor, I'm quite sure mine's a feed-forward... (envelope is taken from orginal signal, not amplified, or something like that)
So the signal is still "smaller" that is why there is a need for a bias trimpot. It basically makes sure how much the transistor is "on", AND how bright the LED is before encountering the guitar signal (I'll call this "starting brightness"). Or, I can always make the starting buffer into a booster, right? It *would* solve my problem of it being out of phase with original signal...
I was planning to use a 9v - 680k - 100k trim - gnd network to establish a proper bias. Max voltage from that would be around 1.15v. Probably won't burn the transistor out. I can still add that inverted diode for extra protection... Anyway, I tried it and works really well. A very fine control of the "starting brightness" of the LED.
When I said "swapping the LED" I was citing an example of us DIY'ers having different LEDs, with different "on" voltages, blah blah, you get the point... :icon_lol:
I do agree with removing the 5k pot... not really useful, but useful in some ways...
The CLR-pot network would work, but with different LEDs around 10k might not make much of a difference. What do you think of letting it control the amount of guitar signal entering transistor base?
Quote from: jfrabat on October 17, 2020, 09:24:00 PM
Interesting... Needs a couple more components, but it certainly IS simple! And it works! (would not trade it for my Engineer's Thumb, but it does work!)
engineer's thumb, is that like m1 Garand thumb? where you get your thumb between the receiver and bolt while pressing in an ammo clip not forcefully enough
From some tests, I noticed that the CLR need not be changed with different LEDs (just for testing pitposes), only the bias has to be tweaked slightly with each LED...
I want to know if this applies with all LEDs... I wanted to test with superbright LEDs, but I happen to have none... :icon_redface:
And so I would want to ask, if any of you have any superbrights, could you try throwing this portion of the ckt on the breader...? :icon_redface: :icon_redface:
Schem...
(https://i.postimg.cc/ZWC47fzL/image.jpg) (https://postimg.cc/ZWC47fzL)
Basically just throw in LEDs and adjust the trimmer until LEDs are slightly lit and when guitar/instrument is strummed hard there is considerable sweep...
I'm sorry for any inconvenience/annoyance this may cause... :icon_redface:
Question for those who built this compressor...what is your opinion now.
Does it work well enough to box up?
Or is it just a novelty with glitches.
Quote from: Phend on November 14, 2020, 07:56:11 AM
Question for those who built this compressor...what is your opinion now.
Does it work well enough to box up?
Or is it just a novelty with glitches.
Erm I'm not sure anyone built is except me... it works, but I would probably want to improve it a bit more... maybe try to figure out the attack/release/decay mechanics, but for you, probably use the new envelope follower that I posted on the post just above yours, @Phend, and the same boost circuit as the latest rendition... remove the 5k limit pot and connect the - wait, maybe I should just stop blabbering and provide a schem, right? Here...
Does this work? https://imgur.com/c8lRu7T
HTH
Thank you very much 11-90-an.
Just got 3 bread boards in the mail.
Did not have any before so I just put my boxes (copied circuits) together and hoped for the best.
Now I would like to do some experimenting, so I will give your circuit a try.
I am just learning about these effects in general. I do know a little, like today it dawned on me that the guitar generates AC in a many many frequencies, the input cap and output cap remove some.
Plus the output cap stops any DC from going to the amp, that is what turned on the light bulb.
Now to get into the middle of the circuits and try to Visualize what is going on.
Thanks again
Paul