The recent 'Tube power amp simulation' thread got me thinking about phase splitters, output transformer-like diffamps and envelope-controlled clipping threasholds.
http://www.diystompboxes.com/smfforum/index.php?topic=110269.0
Eventually, I found a place for all this on my breadboard.
It is a work in progress, but works as expected and gives quite a nice mild-to-moderate overdrive, with the option of some fairly substantial not-too-distorted compression. Not sure that it sounds like a power amp, so I figured I would start a new thread. Will make a recording over the weekend and can provide an explanation of what is going on if it is not obvious.
(https://dl.dropboxusercontent.com/u/11996927/Dirty_Comp.png)
Looks nice.
Is there any sims? Any pics of the output wave form?
Yes, I have an LTspice sim, but not at hand - will post some oscilloscope traces when I get the chance.
It shows fairly soft clipping with predominantly odd order harmonics if the symmetry pot is maxed. As the symmetry
pot is wound back, the clipping becomes more pronounced and asymmetric and even order harmonics grow in.
cool...look forward to hearing it.. 8)
Quote from: samhay on March 13, 2015, 12:57:06 PM
The recent 'Tube power amp simulation' thread got me thinking about phase splitters, output transformer-like diffamps and envelope-controlled clipping threasholds.
I always think about these 'Tube power amps simulation' using 3 legged devices (BJTs or Mosfets) not ampops... the difficult part for me is how to dynamically control the bias point as a function of the input amplitude signal...
P.S.
Going to try and do some sims...
I'd imagine you could run the output of the envelope detector (IC1B) to one or more of the VB points instead of the junction between the diodes to accomplish a floating bias point. I think it would do much the same thing as it's doing now, but I haven't looked that far into it.
I personally think this looks pretty cool. I would put D6 in series with V+ so that it actually protects against reverse polarity rather than fighting to the death with power supply, and leaving the circuit unprotected after it loses. I can't imagine that diode drop will make much difference in a dirt box like this, but you could use a shottky to keep that minimal.
Looks nice, I always loved opamps over JFETs because they are way more predictable, Can't wait for a sound demo with all different settings :icon_lol:
Also, how about asymmetrical set of diodes for the feedback loop of the first opamp, that will sound more tube-ish, am I right?
Quote from: tca on March 13, 2015, 06:32:49 PM
I always think about these 'Tube power amps simulation' using 3 legged devices (BJTs or Mosfets) not ampops... the difficult part for me is how to dynamically control the bias point as a function of the input amplitude signal...
P.S.
Going to try and do some sims...
Perhaps the easiest way would be to use a BJT phase splitter feeding 2 MOSFETS (they are suposed to be pentode-like) with their gate bias tied to an envelope detector. I have thought about getting this to work, but it is a little fiddly as you can't have much swing in the bias voltage before it is either off or on, and you also need to match 2 MOSFETS...
Quote from: ashcat_lt on March 13, 2015, 07:42:38 PM
I'd imagine you could run the output of the envelope detector (IC1B) to one or more of the VB points instead of the junction between the diodes to accomplish a floating bias point. I think it would do much the same thing as it's doing now, but I haven't looked that far into it.
I personally think this looks pretty cool. I would put D6 in series with V+ so that it actually protects against reverse polarity rather than fighting to the death with power supply, and leaving the circuit unprotected after it loses. I can't imagine that diode drop will make much difference in a dirt box like this, but you could use a shottky to keep that minimal.
Thanks. The issue I have with playing with the op-amp bias is that you can quite quickly run out of headroom - the envelope can swing 1-2 V below Vb in this circuit - and end up clipping the rails. This is a good approach if you are playing with a Rat, but not so much if you don't care for op-amp clipping.
The schematic is a bit of a cut and paste job. If I build it, I will use a 1N5817 in series with V+. I will update the schematic at some point to show this, and to also add an LED to monitor the envelope voltage (i.e. sag).
Quote from: sajy_ho on March 14, 2015, 03:48:41 AM
Looks nice, I always loved opamps over JFETs because they are way more predictable, Can't wait for a sound demo with all different settings :icon_lol:
Also, how about asymmetrical set of diodes for the feedback loop of the first opamp, that will sound more tube-ish, am I right?
Thanks. Designing with op-amps can certainly be a lot more predictable than with FETS, and there is usually less issue with other people trying to get it to work too. I also like the simplicity in the biasing of op-amps vs discrete transistors - you can save a lot of coupling caps using op-amps.
You could certainly add just about any combination of diodes you like to the the first op-amp, and the usual switchable options can be had. I kept it symmetrical because I was thinking about power amp distortion at the time and because I wanted the focus to be on the clipping from D3 and D4. Also, the symmetry pot lets you adjust the symmetry of the overall clipping from very asymmetric (min symmetry) to very symmetrical (max symmetry).
Quote from: samhay on March 14, 2015, 06:52:39 AMThanks. The issue I have with playing with the op-amp bias is that you can quite quickly run out of headroom - the envelope can swing 1-2 V below Vb in this circuit - and end up clipping the rails. This is a good approach if you are playing with a Rat, but not so much if you don't care for op-amp clipping.
Which almost leads me back to the comment I didn't actually post about using an lm324 here. With that many components hanging off the opamps, it could get ugly trying to use a quad opamp, but the lm324 will allow you to swing quite a bit closer to the bottom rail than the tl07x and might be just enough. I tend to think that if the signal is loud enough to slam into the rails even with the diodes in the feedback path, any opamp clipping is likely to be pretty well lost in all the other distortion coming out of it, especially if it's asymmetrical from hitting the bottom rail and not the top, but I know that many people just won't tolerate it. Higher rail voltage would obviate the issue, of course, but...
Looks very interesting, can't wait to hear it!
K. Quick question. I know you said it's not tested or verified or anything, but I'm wondering about the time constants that you've chosen in the detector circuit. Best I can tell, most of the integration there comes from the Attack pot (in series with R5) and C5. By my calcs, that will give a range of cutoffs from about 0.7 to around 30Hz. Pretty sure the 10n is too big to touch anything that passes that, just there for RF rejection etc. My question is, is that range based on some real-world numbers for actual rectifier sag, or just eyeball numbers to be tuned by ear? Is there someplace or some way of figuring the approximate time constants for typical amps? Tubes are pretty opaque to me ATM. Ironic I suppose, since they're usually a lot easier to see through than an opamp. :icon_wink:
Edit - I guess while we're on it, what about the magnitude of the sag? How far (maybe in terms of ratio or percentage of total power supply voltage) do the real amps actually droop when they really get cranking?
Quote from: samhay on March 14, 2015, 06:57:46 AM
You could certainly add just about any combination of diodes you like to the the first op-amp, and the usual switchable options can be had. I kept it symmetrical because I was thinking about power amp distortion at the time and because I wanted the focus to be on the clipping from D3 and D4. Also, the symmetry pot lets you adjust the symmetry of the overall clipping from very asymmetric (min symmetry) to very symmetrical (max symmetry).
Ohhh sorry for my stupidity, there is a symmetry control right there :icon_mrgreen:
How about running the circuit on higher voltages to get more dynamic range?
Some oscilloscope traces measured with a 200 Hz sine wave of ~ 100 mV (top) and 1V (bottom) peak-to-peak amplitude.
All measured with gain and comp at max and symmetry either max (left) or min (right).
With the comp turned at least part way, it can take at least 2V peak-to-peak before you can see any obvious clipping from the op-amps, so I don't think there is any need for a larger voltage supply and/or rail-to-rail op-amps.
'View image' for a larger version.
(https://dl.dropboxusercontent.com/u/11996927/DiSCO_OScope.png)
Quote from: ashcat_lt on March 14, 2015, 12:01:50 PM
K. Quick question. I know you said it's not tested or verified or anything, but I'm wondering about the time constants that you've chosen in the detector circuit. Best I can tell, most of the integration there comes from the Attack pot (in series with R5) and C5. By my calcs, that will give a range of cutoffs from about 0.7 to around 30Hz. Pretty sure the 10n is too big to touch anything that passes that, just there for RF rejection etc. My question is, is that range based on some real-world numbers for actual rectifier sag, or just eyeball numbers to be tuned by ear? Is there someplace or some way of figuring the approximate time constants for typical amps? Tubes are pretty opaque to me ATM. Ironic I suppose, since they're usually a lot easier to see through than an opamp. :icon_wink:
Edit - I guess while we're on it, what about the magnitude of the sag? How far (maybe in terms of ratio or percentage of total power supply voltage) do the real amps actually droop when they really get cranking?
It's tested in the sense that it is sitting on my breadboard and works as drawn.
The envelope attack and decay setting are largely set, as you said, by C5 and the attack pot + 2k2 resistor (attack) and R8 (decay). The 10n cap across the comp pot does smooth the envelope significantly too. I was thinking of using an NE5532 for IC2, so might drop the 2k2 resistor to get faster attack settings, but having tried this, I can't hear much difference. These values are not set in stone, but I wouldn't want to make R8 much bigger as this will start to cause issues with how much comp one can dial in.
It's a good question about typical amp sag behaviour. I have no idea, and just chose time constants based on slower compressors and then fiddled until it sounded ok.
With a bridge humbucker and the gain, comp and symmetry set to max, the sag can swing from 4.5V down to about 2.1V, at which point it is probably hitting the op-amp rail. I don't think this is too much of an issue (hitting the rail) as you certainly don't need any more squish at this stage. It does do some funky stuff to the clipping, giving rise to crossover-like distortion, but this doesn't sound too bad.
Quote from: samhay on March 14, 2015, 06:47:44 AM
Perhaps the easiest way would be to use a BJT phase splitter feeding 2 MOSFETS (they are suposed to be pentode-like)...
You can simply turn it into triode-like ;) using a Schade bias (by adding a resistor). This will not work, of course, for all mosfets for reasonable values of current. It depends on the characteristics of a given device.
Quote from: samhay on March 14, 2015, 06:47:44 AM
... gate bias tied to an envelope detector. I have thought about getting this to work, but it is a little fiddly as you can't have much swing in the bias voltage before it is either off or on, and you also need to match 2 MOSFETS...
Yes, setting the bias voltage is tricky but if you have a way of tackling the symmetry of the positive/negative part of the signal the matching is not needed. Setting the bias with a peak detector sounds feasible, but I always take this as a artificial way of doing it -- unelegantly way, I mean.
My approach to this puzzle has always been to build an real class AB amplifier where sag naturally occurs. Power source sag will also introduce varying bias and crossover distortion.
For mosfets this is a challenging puzzle, you need current to get the the device working in a "good distortion region" but also not to much of it because you need a class AB amp not class A. Still tinkering...
This pretty much has to produce all crossover distortion. The TS-style clipper at the front is basically the kind of distortion you get when it overlaps at the crossover region, and the other thing must be creating gaps in the crossover. Theoretically you could dial it in to where they undo each other, but where's the fun in that?
Is this where the sag is on real tube amp? I mean, does the dropping supply voltage not start to clip off the top of the waveform?
Edit - cause I thought about it a bit more and nobody has replied yet -
Correct me if I'm wrong, but what I see this thing doing when the envelope starts actually moving is basically just shifting soft-clipped waveform up and down with respect to the gap at the "zero crossings". That will probably change the harmonic content, but it won't change the dynamic range unless it manages to slam the bottom of the wave into the rail of the differential amp.
Like I said, IDK about real amps, but I always thought sag was more of a "walls closing in" type thing, maybe more like a dying battery on fuzz box.
This is a LTspice sim of the circuit with the gain and comp at max and the attack pot set to 10k. The input is 100mV at 200 Hz. I have taken the output from IC2B and the envelope detector, hence they are swinging around 4.5V.
I think you can see that there is some compression happening?
In any case, this circuit was not designed to emulate a tube power amp - we'll leave that to the other thread. This is a dirty (i.e mildly distorting) compressor and overdrive that might just sound a little bit like a power amp somewhere.
(https://dl.dropboxusercontent.com/u/11996927/DiSCO_SpiceTrace1.png)
It certainly is compressing quite nicely. I think I know where I was wrong last night, but is there any way you can zoom in on that last shot so we can see a few individual cycles when it's squished?
Samples. please?
Quote from: ashcat_lt on March 15, 2015, 11:20:49 AM
It certainly is compressing quite nicely. I think I know where I was wrong last night, but is there any way you can zoom in on that last shot so we can see a few individual cycles when it's squished?
Have updated the simulation output with the early and late waveform below - click on the picture to make it bigger, but I don't think you will see much difference.
Quote from: ggedamed on March 15, 2015, 01:45:59 PM
Samples. please?
Working on it, but struggling to find enough quiet minutes to get something set up - might have to wait until Monday, or if that doesn't work, next weekend.
Thanks. Not exactly what I expected to see, but I'm not really surprised to be wrong. :)
I find it difficult to visually extrapolate the response curve when it's applied to a sine wave because wines are already curvy. Triangle waves just kind of show you the in/out function as long as there isn't a lot of filtering going on around the non-linear portion.
I tried to record something last night but was scuppered by a little problem that only manifest it when I tried to record direct to my audio interface. I think that IC1A was oscilating as it was making an unpleasant craking sound when I played certain notes. There is nothing unusal about this stage, so I guess I just need to lay everything out again on the breadboard and perhaps take a look at the way I generate Vb. This isn't going to happen until the weekend.
In the mean time, I have updated the schematic to show a few minor tweaks I have made.
you little teaser... ;D
I am probably being a bit picky, but this is supposed to sound good without the gain turned all the way up (which does sound rather nice). At the moment, it looks like it either needs a bit more attention to breadboard layout and/or a design tweak. I don't think there is anything majorly wrong with it, but I'm away for the week, so you will have to spend the next few days squirming in anticipation.
However, if anybody wants to throw it on the breadboard and give it a try in the mean time - it's neither particularly big, nor uses any mojo parts - then that would be great.
i'm squirming... ;D
Seems the distortion I didn't like was a grounding problem with my audio interface and/or pedals rather than the circuit. It has started raining again and I guess the humidity sorted it out, as it has gone.
Here is a very quick and dirty audio sample recorded with a touch of reverb direct to the audio interface. Having listened to it, I can surmise that it probably needs some EQ* and I can probably dial back the compression a bit. I guess I should have also have recorded something with the gain turned further down too. Anyway, some of the settings sound pretty good I think, but there will be a few more tweaks before it is ready to box.
*I have flatwound strings on the guitar at the moment so everything sounds dark, but I should probably drop the value of C1 and/or make this switchable.
https://dl.dropboxusercontent.com/u/11996927/DiSCO_audio1.mp3
Sounds good man! I think the clipping is a little strange but compression is awesome. Also you're right about the dark sound, lowering the caps would be nice too.
IMO adding a three band EQ or maybe a little mid scoop will make it a killer pedal :icon_twisted:
I gave it a few tweaks last night and added some more aggressive HP filtering to the first clipping stage, which makes for a significant improvement in both tone and clipping behaviour.
I also realised that the compression doesn't work very well when the symmetry pot is at minimum as the half wave rectifier doesn't get much left to work with - I can/will fix this with a redesign of IC1B.
I have also been trying passive tone controls tacked onto the output of 1C2B - mainly SWTC and variants. Not sure I have found anything I like yet, but it is proabably going to make for a useful addition. Any suggestions?
I should have a little quiet time this evening to update the schematic and audio clip.
Schematic updated - works significantly better now with only a somewhat modest increase in parts-count.
Still haven't settled on a tone control, but the Drive / gain stage has some variable tone control built in now - essentially some pre-emphasis when the Drive pot is centred.
Recording / audio interface problem is back, so no new clips for the moment.
Nice job man, How about adding this one as tone stack:http://www.runoffgroove.com/tonemender.html
I used it in some of my builds and I love the marshall mod.
Sam - a bit OT and probablya bit dumm too - but can you explain how the comp indicator works and how you've adjusted it.
Erik
Quote from: sajy_ho on March 27, 2015, 01:56:07 AM
Nice job man, How about adding this one as tone stack:http://www.runoffgroove.com/tonemender.html
I used it in some of my builds and I love the marshall mod.
Thanks - I was thinking 1-knob and passive, so that it will still fit in a 1590B., but it's a good suggestion and would make for a more complete amp-in-a-box effect.
Quote from: lion on March 27, 2015, 06:01:26 AM
Sam - a bit OT and probablya bit dumm too - but can you explain how the comp indicator works and how you've adjusted it.
Erik
No problem. The indicator monitors the voltage of the buffered clipping threshold, so as the compression / sag increases, the voltage drops and the LED turns off.
You may be confused by the use of 2 resistors? If so, this approach is taken from the 'Tremulus Lune', but I'm sure it has been around longer than that. R14 is the current limiting resistor for the LED and R15 acts as the other half of a voltage divider to bias the LED's anode to about half way between the monitored voltage and ground. This makes the LED much more sensitive to the changes in the clipping threashold.
If you are wondering why I chose to use 2k2 resistors, then there are 2 reasons - the bright red LED I am using lights up nicely with them and I ordered more of them than I was intending, so tend to use them when I can. If you use another LED that needs more/less current then these resistors can be tweaked to taste.
I really like your idea for this. Would be interesting to do a fet/fet/fetzer based compressor for line level stuff for recording...
Quote from: samhay on March 27, 2015, 09:43:23 AM
.......so as the compression / sag increases, the voltage drops and the LED turns off.
Ahh - LED turns OFF (obviously) :icon_redface:
Thanks Sam.
Erik
Quote from: jtn191 on March 28, 2015, 02:51:27 PM
I really like your idea for this. Would be interesting to do a fet/fet/fetzer based compressor for line level stuff for recording...
Thanks.
The idea of this design is to use diodes to add non-linearity, but some of the ideas could be used elsewhere. How were you thinking of doing envelope-control of a FETzer?
Quote from: lion on March 29, 2015, 04:50:21 AM
Quote from: samhay on March 27, 2015, 09:43:23 AM
.......so as the compression / sag increases, the voltage drops and the LED turns off.
Ahh - LED turns OFF (obviously) :icon_redface:
Thanks Sam.
Erik
I guess this is only obvious if you look at the schematic - one typically sees an LED light up as a compressor compresses. However, I haven't found a good way to do this here without significantly adding to the parts count.
Quote from: samhay on March 23, 2015, 06:08:22 PM
https://dl.dropboxusercontent.com/u/11996927/DiSCO_audio1.mp3
Recording setup is behaving itself today, so make a quick direct recording while twiddling pots. The link above is now to the newer recording.
My apologies for the poor metering, but the volume pot is not very accessible on the breadboard and this was all recorded with the level set to the same place.
Quote from: samhay on March 29, 2015, 09:19:45 AM
Quote from: samhay on March 23, 2015, 06:08:22 PM
https://dl.dropboxusercontent.com/u/11996927/DiSCO_audio1.mp3
Recording setup is behaving itself today, so make a quick direct recording while twiddling pots. The link above is now to the newer recording.
My apologies for the poor metering, but the volume pot is not very accessible on the breadboard and this was all recorded with the level set to the same place.
Nice demo! I breadboarded your circuit and I'm getting some neat tone out of it, Also I tried jfets as diode pair in the feedback loop and got interesting results.
Thanks for breadboarding - it is always nice to have multiple sets of ears to audition things with.
There are still a few things I would like to tweak with the circuit and the feedback clipping in the first op-amp is one of them. I'm still trying to decide whether a tone control is necessary, but also wondering if it would be useful to have variable release times too (make it more of a real compressor). Other than that, it seems to be doing everything I set out for it to do, so will start working on a layout soon - probably vero.
Quote from: samhay on March 31, 2015, 04:37:04 AM
so will start working on a layout soon - probably vero.
Some of us would be grateful to you..!!! :icon_biggrin:
I haven't built anything on vero for quite a while, and my recent reverb build on perf has sated my desire to work with that medium for a while, so will put the layout at the top of my list (once I have settled on a final design).
Hi Sam-
Is the schematic in the first posting (version 1.2) correct?
I think that is what I have on the breadboard at the moment, so it is correct in the sense that it works. However, I have some final tweaking to do, so there may be a few changes before I build it.
5 pots, it'll have to go in a big box, that would be a nice change of pace. It sounds nice, looking forward to whatever improvements you have in mind.
Great job! I like the demo. :)
Maybe a bit early, but I took the liberty of doing a vero layout
(http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/7017792_orig.png)
Full Size version (http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/disco.png)
It's not verified, but it should match the schematic. :)
Here (http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/disco_dirty_compressor.diy) is the file for DIY Layout Creator (version 3.28.0)
So you can do any changes to the layout yourself.
But I will make changes to your upcoming tweaks aswell.
Thanks for sharing your project!
cheers
Freppo
Nice one Freppo.
I tend to leave things on the breadboard for quite a while before deciding whether to build them. In this case, I had another play with the circuit last night and added a release control, which was quite useful. I think I might refine the side chain a little too, and then have to decide whether to leave the SYMMETRY pot as-is, or make it switchable...
Anyway. It might take a while before I settle on a final version, but I will leave the current version of the schematic here for reference, and continue to undpate the schematic on the 1st page until I settle on a 'final' version.
Freppo's layout version:
(https://dl.dropboxusercontent.com/u/11996927/Dirty_Comp0.png)
Have updated the schematic in the first post to a probably-final version.
Freppo - I noticed that C4 should be 220p rather than 1n, which I have updated on the legacy schematic above too.
The latest design iteration has a slightly tweaked envelope detector with added release control and faster attack.
I have also replaced the symmetry pot - I tended to only use either extreme - with an on-off-on toggle switch that can also switch in asymmetric clipping in the first gain stage (edit - have re-oriented these in the updated schematic to emphasise even-order distortion). The 3 different clipping options are fairly subtle, but give a little more range/flexibility.
I have also added a Millennium bypass option that uses the compression indicator as the status indicator (the LED doesn't tend to go completely off under max compression). I haven't tested this, but would be surprised if it doesn't work.
For a final test, I need to put new strings on my guitar. Will put something brighter on and see whether we can get away without having a tone control.
For reference, the simulated frequency response looks like this. Different traces are simulated with the gain pot settings. Input signal is at 1dB.
(https://dl.dropboxusercontent.com/u/11996927/DiSCO_frequency.jpg)
Hi Sam-
Thanks for posting, I look forward to breadboarding V1.3 this evening.
One thing on the Compression Sag monitor- you might want to move the LED and its parallel resistor to the drain side of the MOSFET. I had problems with your arrangement in the past, and subsequently found the Millennium bypass works best with the source wired to ground.
Cheers, Russ
OK, sounds like I had better give the bypass a test - thanks.
Happy breadboarding.
Gave it a test with new much brighter strings. Still sounds ok without any need to tweak the EQ, so happy to go sans tone control.
It works as a pretty decent compressor - can do a reasonable job with chicken pickin' through to smooth sustain. There is some pumping and breathing with some settings, but this could be seen as part of the charm.
Tested the bypass with the first random 2N7000 I could find. Worked fine once I got the pinout right.
I think the 1.3 version in the first post can be considered 'final' and is likely to be the version I box up.
Hi Sam-
I've got it on the breadboard, and it has a good range from clean to crunch. I'm with you, it doesn't need a tone control. Not too much time to play with it yet, but I think its a winner, worthy of boxing up :icon_biggrin: Hmm, wonder what it'll fit in?
Russ - glad you like it.
I guess you could replace the attack and release controls with trimmers or switches, which should allow one such as yourself to squeeze it into a 1590a. I feel like spreading out a bit, so will aim for 1590b.
Can't decide wether to paint the box pink (distortion) or neon lime (compressor). Decisions decisions
Quote from: Cozybuilder on April 04, 2015, 08:47:54 AM
Can't decide wether to paint the box pink (distortion) or neon lime (compressor). Decisions decisions
perfect combination of colours for stripes, in my colour palette.
I added Big muff's tone control to this but ended up omitting it, so I have to say you're right about no need for tone control.
Right now I'm working on a PCB for this circuit and will post it as soon as possible. It deffinitly takes a place on my pedalboard.
Thank you Sam.
I made the changes to my vero layout. :)
I had to compromise alittle to keep the size 1590B friendly,
so I didn't include the millenium switching and kept the comp LED as the 1.2 version.
(http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/4652113.png?342)
Full Size version (http://parasitstudio.weebly.com/uploads/2/4/4/9/2449159/disco.png)
cheers / Freppo
I've had a chance to play with it a bit, you did a great job with this Sam! Now to paint a box for it (stripes?)
It should look a little better than this once boxed:
(http://i1362.photobucket.com/albums/r688/russrutledge/Zombie%20Chorus/DSCN2465_zpsqohveqhc.jpg)
Quote from: Cozybuilder on April 04, 2015, 08:47:54 AM
Can't decide wether to paint the box pink (distortion) or neon lime (compressor). Decisions decisions
Quote from: Cozybuilder on April 05, 2015, 02:35:57 PM
I've had a chance to play with it a bit, you did a great job with this Sam! Now to paint a box for it (stripes?)
Well pink and green stripes might look very cool, but you probably won't have room for many stripes if you are planning on building it in a matchbox.
Alternatively, if you mix pink and green, you get brown...
Glad you like it. I see we went to the same school of spaghetti monster breadboarding too.
Quote from: sajy_ho on April 04, 2015, 10:45:16 AM
I added Big muff's tone control to this but ended up omitting it, so I have to say you're right about no need for tone control.
Right now I'm working on a PCB for this circuit and will post it as soon as possible. It deffinitly takes a place on my pedalboard.
Thank you Sam.
Thanks for trying out some tone controls with it - I am generally quite nervous designing dirt boxes that don't have adjustable EQ, so it's great to see that there seems to be some agreement here.
A PCB would be great - doesn't look like a trivial build on vero.
Feel free to post it here if you feel like sharing.
Quote from: Freppo on April 04, 2015, 03:22:42 PM
I made the changes to my vero layout. :)
I had to compromise alittle to keep the size 1590B friendly,
so I didn't include the millenium switching and kept the comp LED as the 1.2 version.
cheers / Freppo
Nice job Freppo. I started laying this out on vero last week and quickly realised that it isn't a particularly easy circuit to route.
The 1.2 switching seems like a good compromise, and I would imagine most people will be happy to use 3PDTs anyway.
I built up the vero layout today. :)
It works fine, except the symmetry switch.
With the SW4 / SW5 not connected it turns out a massive square-wave fuzz and has no response to any of the controls.
Correct me if i'm wrong, but don't you still need a 10K resistor from the inverting input to the output of IC2A?
I guess now it's turning into a comparator without it when the input/output isn't jumpered by the switch.
cheers / Freppo
> Correct me if i'm wrong, but don't you still need a 10K resistor from the inverting input to the output of IC2A?
Sorry - that's correct. It looks like I forgot to add the 10k to the schematic (now updated).
It looks like you have enough room in your layout to add the resistor if you stand it up.
Wow, that 10K in the feedback loop makes a huge difference! Now the two switch positions are a lot more compatible. I thought I had miswired and was about to start troubleshooting, glad I looked at the thread first.
Okidoki. I updated the layout and added the final version to the vero-archives in my blog :)
http://parasitstudio.weebly.com/stripboard-layouts/disco-dirty-compressor-and-overdrive (http://parasitstudio.weebly.com/stripboard-layouts/disco-dirty-compressor-and-overdrive)
I had to make in one column wider, but it will still fit a 1590B if you put the layout sideways.
If it has more then 4 knobs I'll always go for a larger box anyway, but that's just my personal preference. :)
I will post some picture when/if I get around to boxing it.
Thanks again for sharing this project!
cheers / Freppo
No problem Freppo, and sorry about the schematic %^&*-up. I hope that the rest of the builds go without incident.
Side note. Freppo - I see you also did a layout for the 'Cherub'. If you built it, what do you think?
I enjoyed your Cherub Chorus alot. It sounds great.
Just another project that I never gotten around to boxing. :icon_rolleyes:
The only negative thing about the cherub (aswell as the dimension p) is that I find them are a bit noisy (hissy)
I think some hi end pre-emphasis at the front end and some roll-off at the end would reduce most of the hiss.
The pre-emphasis I have in both the Parasite Phaser and the Green Currant Tremolo helps to reduce the noise alot.
Just a thought, maybe worth experimenting with :)
Glad you liked the chorus - I have a Dimension P too, but can't remember how to drive it as I built one with too many options.
I may have got lucky with my build of the Cherub, but it is pretty quiet for a little box with a PT2399, a LFO, and a dodgy layout. My recording interface is playing nice this evening, so I dug it out and recorded a new sample: https://dl.dropboxusercontent.com/u/11996927/Cherub2.mp3
Any chance the hiss you hear is coming from the PT2399 (some are worse than others) - does it get louder with the mix knob?
In any case, it would only cost a couple or resistors and caps to add some pre- and de-emphasis, which is a good idea, so will add it to the list for a revision at some stage.
p.s. no shame in not having boxed it yet. I have mine in a blank box, and it doesn't look like I will be adding labels any time soon.
Sounds great!
Thanks Doug
Good work Sam and Freppo.
Two more to add to the list. It really does sound great too.
Rich
Yeah, you really did a great job capturing the compression and the touch-sensitive power stage distortion here.
Thanks - it was one of those ideas that worked better than I thought it would. Nice to have something that is a just a little different too.
Finally finished- thanks for one of my favorite pedals Sam! I really like this at the beginning of the chain- just a little OD sounds great with the other pedals, the compression really smoothes out the overall sound. Versatile.
(http://i1362.photobucket.com/albums/r688/russrutledge/Disco/DSCN2511_zpsifmqtplw.jpg) (http://i1362.photobucket.com/albums/r688/russrutledge/Disco/DSCN2507_zpsjkzova6t.jpg)(http://i1362.photobucket.com/albums/r688/russrutledge/Disco/DSCN2508_zpsrzr3dktj.jpg)
(http://i1362.photobucket.com/albums/r688/russrutledge/Disco/DSCN2510_zpssmc4dnkz.jpg)
Nicely done Russ.
I see why you went for 2 LEDs now - very period correct.
Just noticed another error in the ver 1.3 schematic, which I have now fixed.
SW2A (Symmetry switch) should only be shorting D3. As it was drawn, it was also taking D1 out of circuit when the switch was open - not the intendend function, so I have moved D1.
Freppo, in your layout, you will need to shift the anode of D7 (your labelling) down to the op-amp output - it will fit if you move it left 2 rows.
Russ, not sure how you wired your switch, but it will probably work better if you do it as now drawn.
Sorry guys.
This was the schematic I used, D1 is always in the circuit paralleling D2, D3 gets shorted. In your post above, the difference is that D1 will parallel the pair D2 and D3, or only D2. I can do that by switching the 2 leads to SW1A (D1 to SW1A center, and D3 to SW1A #3.) Right?
(http://i1362.photobucket.com/albums/r688/russrutledge/Disco/DSCN2495_zpsrd32jx8u.jpg)
First, I should stress that if you like the sound of it now with the gain turned up, then it might not be worth trying to 'fix' it.
The problem with the way I had drawn it is that D1 shouldn't be connected to the junction of D2 and D3 but rather between the 2k2 resistor and the op-amp output. Changing your wiring won't fix this, you need to move the D1 anode to lug 1 of the gain pot / op-amp output by breaking the connection to the D2-D3 junction.
Quote from: samhay on April 23, 2015, 08:00:52 AM
Freppo, in your layout, you will need to shift the anode of D7 (your labelling) down to the op-amp output - it will fit if you move it left 2 rows.
Russ, not sure how you wired your switch, but it will probably work better if you do it as now drawn.
Okidoki. I will fix it and update the layout :)
cheers / Freppo
I see my description was badly worded, that would short out D3. I meant move the anode of D1 to SW1-2 (the junction of op-amp out and gain). The D2-D3 junction remains intact at SW1-3. Perf usually isn't a whole lot of fun to modify, however on this build D1 is at the bottom of the row of 3 diodes with an empty hole next to it, making the change straight forward. (well, after disassembly :P )
Do you still have this on breadboard? Can you test out the way mine is currently wired to see if there is much difference in the sound? If you think its significant, I'll do it.
Thank you,
Russ
Yes - perf's shortcomings become significant when you have to make mods. Sounds like it should be about as easy as it ever is with your layout, but I will still feel bad about it if you decide to open it up.
I still have it on breadboard and will make a clip of the 2 options. Might not be for a couple of days though.
I'll probably open it anyway. Thanks for a great circuit, growing pains are part of the game.
Here is a quick clip recorded direct with gain at max and a fairly quick attack and slow recovery. SW2B is open, so the second stage (clipping to the moving ground) is symmetrical.
https://dl.dropboxusercontent.com/u/11996927/DiSCO_audio2.mp3
There are four SW2A settings recorded first with depth at minimum, then again at maximum:
1. SW2A closed - symmetrical clipping
2. SW2B open - asymmetrical clipping (latest / updated schematic)
3. SW2B open - old / incorrect schematic with D1 anode connected to the junction of D2 and D3 - i.e. 2 diodes in one direction and none in the other.
4. same as 1.
setting 3 - the wrong one - is cleanest / has the most headroom with the depth at minimum (although if you turn the gain down, the other settings can sound like this). However, with the depth at max, the clipping from the 2nd stage is pretty extreme in this 'setting ' and there is all sorts of compressor fluttering, etc.
In summary - Russ, it is probably worth opening her up. Sorry.
Sam-
Thanks for all- while I don't have the #3 condition, I'm going to change it anyway.
Hey Samhay, any idea how this might sound as an outboard compressor on drums? I've been playing around with the Engineer's Thumb and it's usable!
I have no experience with drum compression.
The Engineer's thumb is a better compressor than the DiSCO, which is primarily an overdrive. That said, the DiSCO can have a fairly quick attack and both attack and release are adjustable over a wide range, which I imagine is quite useful when compressing drums. However, the gain stage is not flat and is voiced for guitar, so it will probably need to be tweaked to play nice with drums - to do this, I would remove R2 and C2, and make C1 somewhat bigger. You may also want to get rid of the symmetry switch and replace the 1N4148s in the first gain stage with LEDs to increase the headroom.
I have a few 'proper' compressor designs in the works. What is it about the ET that isn't ideal for compressing drums?
My particular Engineer's Thumb has the "attack glitch" you hear some people talking about, only really noticeable on guitar. I mean it sounds pretty good...I would change the tapers/values of the attack/release pots. Most of the useful attack range happens in the first 25% of the turn. I don't hear much of a difference with release, though I have measured to ensure it works. I almost bought an Earthquaker Warden to try out as an outboard compressor. A "dirty" compressor would be very interesting to me in this context. Something like a Distressor or 1176. The 1176 has been cloned a lot...may as well go that route eventually.
Looked up the Warden - it's optical so might be fast enough for your needs (but then I am only wildy guessing).
I always suggest you try something on a breadboard before building it. Shouldn't take long to give the DiSCO a try, and I would be interested to hear way you think of it as a drum compressor - I like the idea of a drum overdrive too.
It also occured to me that you can run the DiSCO on higher voltage if you need more headroom - again you may have to tweak the filtering and diode choices though.
I finally got round to building this using my vero layout (below).
The combination of a switch and top mounted jacks makes for a snug fit, but the board fixes to the base happily enough.
Only changes are to the compression indicator / Millenium bypass, which I built as a daughter board. The trim pot parallel to the LED allows a nice adjustment of the LED range.
(https://dl.dropboxusercontent.com/u/11996927/DiSCO_photo3.jpg)
layout - now somewhat verified; save/view for a larger version:
(https://dl.dropboxusercontent.com/u/11996927/DiSCO_vero.png)
Nice work man, I tried to design a pcb layout for this pedal a month ago but somehow I found this circuit way more complex than I thought it would be! So I ended up with an unfinished work.
But your vero layout is awesome and I probably go with it.
Thanks for your sweet sounding circuit man.
Thanks.
The vero layout was a bit more difficult than I was expecting too - it's a bigger circuit than it looks.
It's a credit to Freppo that he could knock up a vero layout so quickly, and the only reason I didn't use his was that I wanted to try to tidy the wiring up as much as possible by putting wires as close to pots, etc. as I could.
Great looking pedal Sam 8)
I'm very happy with mine, its a superb circuit design.
Thanks Russ. Thought I was going to need your cut-offs at one point when I was trying to get the back on, but it all seems to fit ok with a bit or re-arrangement.
I hadn't played with the circuit for a while and I still like it post-build, which must be a good sign.
The symmetry switch seems to work better than expected too, and I'm glad I went to the trouble of including it. The 3 settings all have quite different character, with the asymmetric clipping being somewhat brighter, which makes for a strange sort of tone control. The volume drop when R5 is shorted is only marginally noticeable, which is a relief too.
Got around to re-posting images, etc...
https://samdump.wordpress.com/welcome/projects/disco-disco-2/ [edit - link fixed]
(https://samdump.files.wordpress.com/2018/03/dirty_comp0.png?w=1800)
(https://samdump.files.wordpress.com/2018/03/disco_vero.png?w=1800)
audio: https://www.dropbox.com/s/iyfklmfyr2v6auc/DiSCO_audio1.mp3?dl=0
Quote from: samhay on March 08, 2018, 11:54:08 AM
https://wordpress.com/page/samdump.wordpress.com/130
That blank Sam :(
https://samdump.wordpress.com/welcome/projects/disco-disco-2/ (https://samdump.wordpress.com/welcome/projects/disco-disco-2/)
Quote from: 287m on March 08, 2018, 04:55:37 PM
Quote from: samhay on March 08, 2018, 11:54:08 AM
https://wordpress.com/page/samdump.wordpress.com/130
That blank Sam :(
https://samdump.wordpress.com/welcome/projects/disco-disco-2/ (https://samdump.wordpress.com/welcome/projects/disco-disco-2/)
Thanks - link fixed.
In any case, there isn't anything there that isn't in the above posts.