Thursday 22 November 2012

Engineer's Thumb

Request, with CA3080 instead of LM13700 (but you can use the conversion daughterboard to allow you to use the LM13700 if you prefer).

Designed my Merlin Blencowe and posted on the various DIY sites, this is how he described it:

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:

Up to five times more headroom than a Dynacomp
Less noise than a Dynacomp
Same available sustain as a Dynacomp
Fewer parts than a Dynacomp
Cheaper than a Dynacomp
Feedforward side chain
Possibility for all five controls
Fits in 1590B
Millennium bypass

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)!





Posted by at 21:15
Tags: , ,

102 comments:

  1. johnk22 November 2012 at 23:52

    awesome! thanks for posting this. when i get back from our thanksgiving dinner i'll be building this one.

    ReplyDelete
  2. Kiichi23 November 2012 at 02:09

    Thanks for posting, sounds like this is a must build thing!
    Too bad I don´t have all the parts around. Next time I order I guess...

    Will be fun to compare my MXR supercomp with this and the Rothwell Love Squeze I´ll do over the weekend. I somehow have the feeling that the MXR will get its ass handed to it.

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  3. johnk23 November 2012 at 05:07

    i was actually hoping that Mark was going to post the 5 knob version instead of the two (or three) knob one.

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  4. johnk23 November 2012 at 05:13

    Hmmm, it looks like the +9V and ground are shorted to me, so i think that you meant to move the ground lead up one row.

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    1. mirosol23 November 2012 at 05:39

      Second that. But to me it seems like the ground lead should be two rows down. Taking it one row up would ground the non-inverting input of IC2, which isn't right...
      +m

      Delete
    2. johnk23 November 2012 at 05:42

      yep. you're right. it should go two rows down from where it is now.

      Delete
    3. IvIark23 November 2012 at 09:09

      Ha ha. I moved the ground connection before exporting so the wires were spread out a bit more from where it was, and have gone for the wrong supply row. Layout updated.

      And incidentally John, you have everything you need to make the 5 knob version. Replace the 1M resistor at IC3 pin 3 with a 1M pot for a Threshold pot, replace the 100R with a 50K or 100K pot (or whichever higher value works best) for an Attack pot, replace the 1M next to it with a 1M pot for a Release pot. All simple 2 lug variable resistors.

      It's all there, but it also offers the builder the option of building the smaller 1590B friendly 2 knob option if they want to.

      Delete
  5. kod2nd23 November 2012 at 14:29

    This looks very interesting. bc327 is a pnp? So im guessing 2n5087 would be an ideal replacement?

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  6. rudeez23 November 2012 at 16:06

    would the lm13700 option sound better then the ca3080 or?
    can't remember if the lm13700 actually is a double ca3080 or not..

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    1. IvIark23 November 2012 at 16:10

      Should sound the same. The LM13700 is just like 2 x CA3080s with additional independent buffer circuits too, and none of those extras would be used anyway.

      Delete
  7. mirosol25 November 2012 at 13:30

    Build it. Makes a decent overdrive, but it's not a compressor..

    There seems to be something wrong with the layout. For starters, the 220R should connect CA3080 pin 3 vref, not +9V.. I'm not sure about other stuff...
    +m

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    Replies
    1. IvIark25 November 2012 at 13:47

      I'll check it over mate

      Delete
    2. IvIark25 November 2012 at 14:04

      Yes the 220R needs to go one row lower, layout updated. Nothing else stood out

      Delete
    3. dexxyy25 November 2012 at 15:43

      having a look at the layout, there`s a shared link in the row below ic2 but nothing else is connecting in that row, why the link?

      Delete
    4. JaviCAP25 November 2012 at 15:53

      This comment has been removed by the author.

      Delete
    5. mirosol25 November 2012 at 15:58

      Yup. That makes it a compressor :) But i refuse to tag it yet.

      For some reason my attack time is close to 10 seconds, which means that playing chords with this is impossible..

      I'll eye it out...
      +m

      Delete
    6. mirosol25 November 2012 at 15:59

      Dexxyy: Because the 220R was connected to it.
      +m

      Delete
    7. IvIark25 November 2012 at 17:16

      Yes it's unnecessary mate. I do that before I start the layout properly so all the power connections for the IC are made and with one in between row also getting the power connections which is useful sometimes to allow filter caps and other components to connect to 9V or ground. In this instance the row wasn't required for anything else and so the double link could be removed. You could even lose that row completely if you wanted to to make the layout smaller.

      Delete
  8. Gc6627 November 2012 at 09:18

    Where does everyone get these strip boards that are 20 deep. Looks like tayda only goes 19 nowhere near 20+

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    1. mirosol27 November 2012 at 09:25

      I get mine from musikding and banzai (depending on how much other stuff i need for the same order) Both have the same boards and i buy them as 10x16cm pieces.
      +m

      Delete
    2. IvIark27 November 2012 at 10:27

      Rapid Electronics

      Delete
  9. kod2nd27 November 2012 at 21:44

    Is the attack time fixed?

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    1. IvIark27 November 2012 at 22:10

      It says in the notes, increase the 100R to increase the attack. Or swap it for a pot if you want that control.

      Delete
    2. mirosol27 November 2012 at 22:13

      I didn't have time to check my build yet...
      +m

      Delete
  10. mikejoyce28 November 2012 at 22:17

    any further developments on this one?

    ReplyDelete
  11. mirosol29 November 2012 at 15:05

    Yup. I went through it today. My issue was with release more than attack.

    I took wires outboard from 1M and 100R, breadboarded the wires with 1M and 20K trimmers. For me, 20K is good value for attack, and 430K is good for release. I'm still going to decrease the ratio pot for 500K log, as the 1M seems to be quite unusable.

    Layout works, but those three values should be played with...
    +m

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    Replies
    1. IvIark29 November 2012 at 17:10

      Do you think it can be verified now then mate?

      Delete
    2. Olav29 November 2012 at 17:43

      drumroll...............

      Delete
    3. mirosol29 November 2012 at 18:08

      Well :) I did tag it after i got it working the way i wanted. So i can say it's safe to build. Everyone building it should just know that those two (or three) values may need tweaking. This behaviour may have something to do with my CA3080, but only thing wrong with it was just the attack/release times to begin with.. (after that 220 found its home)

      I'm confident that the layout is ok.

      Mark, you could take the unnecessary strip away..
      +m

      Delete
  12. johnk1 December 2012 at 01:28

    i built one of these (the 5 knob version) using another vero layout with an LM13700 and it works great, so next i'm going to build Mark's layout with the CA3080 just to see if there's any difference between them.

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    1. mirosol1 December 2012 at 07:26

      Oh Please do! I'd love to get build confirmation from someone else too.
      +m

      Delete
    2. johnk1 December 2012 at 07:55

      Hi Miro,
      i'll see if i can get one built up by tomorrow. i think that i see a couple of small differences in Mark's from the one that i built, but it looks basically the same.

      i also drew up my own LM3080 version before Mark posted his, but it has four standup resistors to keep the size of the board small (mine's 21x15), and i know how he hates standup resistors. ;-)

      Delete
    3. johnk1 December 2012 at 22:12

      i just finished it and have been testing it (i built it with the 5 control knobs). it passes signal fine but it doesn't have any compression whatsoever. i'm going to disconnect all of the pots with the exception of the volume and ratio to see if it works that way.

      Delete
    4. mirosol1 December 2012 at 22:18

      Curious.. Mine had massive compression that did release in about 10 seconds. Tweaking the 100R and 1M helped... Could it be that those CA3080s are sensitive to something we don't know about?
      +m

      Delete
    5. johnk1 December 2012 at 23:07

      i don't think that it's the 3080. i built another comp that uses it and it worked perfect the very first time. i'll have to check and make sure that i didn't make any errors on the build, but i'm pretty sure that i didn't.

      Delete
    6. johnk2 December 2012 at 03:25

      okay, i removed the three extra pots and now it's just like Mark's layout above (i.e., it just has ratio and level controls). it works perfectly (and sounds very good!). either i screwed up the wiring with the additional pots, or i had a build issue somewhere else that got solved with removal of the pots. i'm going to start adding one control at a time now to see if i can make it work with all 5 of them again

      Delete
    7. johnk2 December 2012 at 05:29

      i re-added the 'release' control, and it works exacctly as it should, however, i recommend adding a 150K-200K resistor in series with lug 1 so it doesn't create a short for the 1M resistor that the 1M pot replaces when the pot's fully CCW (i.e the fastest release). next, i re-added the attack control and it works as it should too. i remove the 100r reisot from the board and soldered it in series to lug one on the attack pot since you want 100r to be the minimum anyway (fastest attack).

      next up, the threshold control.

      Delete
  13. johnk2 December 2012 at 08:15

    i tried to get the threshold control to work, but no matter how i wired it, i wasn't able to. it works perfect on my other vero layout build, and it seems super simple to install it on this one (and on the schematic here: http://www.freewebs.com/valvewizard2/engineersthumb.html , but for some reason i just can't figure out why it won't work, so i'll probably just leave it out on this one and use it as a 4 knobber.

    ReplyDelete
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    1. mirosol2 December 2012 at 11:18

      Still. Great to hear that i'm no the only one who got this layout to work correctly :) Thanks John!

      BTW.. I thought i'd build a(nother) compressor for our bassist - Any suggestions what design would be perfect for bass? This or some optical, like Forest Green?
      +m

      Delete
    2. johnk2 December 2012 at 15:17

      did you install a threshold control on your's? and if so, how did you wire it?

      out of all of them that i've built, the Keeley 4 knob and the EMMA transmorgrifier are both awesome on bass. i raised the values of the input and output coupling caps on them for use with bass. besides compression, the EMMA can actually get some nice overdriven tones out of it too. i also built a pigtronix philosoher's tone that also sounds great with bass.

      Delete
    3. mirosol2 December 2012 at 22:11

      I didn't try on any extra controls... Maybe i should, as i haven't boxed it - it is laying around on my desk :)

      Currently our bassist is using my modded build of Mr. Squishy. That's ok - not bad at all, but maybe something with more control would be even better. I have Transmorgrifier board unboxes, so i could try that...
      +m

      Delete
    4. johnk2 December 2012 at 22:19

      i like my other ET that has a threshold control 10X better since it can also be used as a clean boost, or even dial in some grit, so i ended up finding a way to add a threshold to Mark's layout. i'll post a pic of it, since adding a threshold is NOT just a matter of replacing the 1M resistor with a 1M pot. the other two controls (attack and release) ARE a matter of replacing two resistors and i prefer to have control over those parameters too.

      funny you mention it, because the Mr. Squishy is already going to be my next comp build.

      Delete
  14. johnk2 December 2012 at 23:51

    and here's how it needs to be if you want build the 5 knob version.

    http://johnkvintageguitars.homestead.com/Effects/Compressors/Modded_Marks_5knob_engineers_thumb.png

    ReplyDelete
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    1. johnk3 December 2012 at 02:08

      here's another pic to show the differences:

      http://johnkvintageguitars.homestead.com/Effects/Compressors/ET_mods_for_5_knob_version.png

      Delete
    2. mirosol3 December 2012 at 05:37

      :D Talk about mods! Great contribution! Thanks John!
      +m

      Delete
    3. johnk3 December 2012 at 06:04

      thanks. there were a couple of errors in the first post pf the mods but the link has now been corrected.

      Delete
    4. kod2nd4 December 2012 at 08:12

      Is there a layout for a 5knob LM13700 version?

      Delete
    5. kod2nd4 December 2012 at 08:22

      scrap that, i found it.

      Delete
    6. Clay3 January 2018 at 01:18

      if you want to build the 5 knob version with the ca3080 use the second layout on this link from john

      http://johnkvintageguitars.homestead.com/Effects/Compressors/ET_mods_for_5_knob_version.png

      the first link you posted does not work john- this one does function properly

      Delete
  15. johnk3 December 2012 at 07:33

    here's a pic of both my CA3080 version, and my LM13700 version. These two comps sound identical (and sound really nice!).

    http://johnkvintageguitars.homestead.com/Effects/Compressors/2-ETs-01.jpg

    ReplyDelete
    Replies
    1. mirosol3 December 2012 at 07:59

      Wow. The LM13700 version is smaller :)

      I just have to ask.. Where do you get that green stripboard?
      +m

      Delete
    2. johnk3 December 2012 at 08:27

      yes, the LM13700 version is smaller due to having 4 standup resistors. one of my local electronics shops carries the green vero. it's really high quality stuff. the trace strips are bonded to the fiberglass really well and bright silver plated copper instead of just bare copper.

      Delete
    3. Lukes0n22 February 2021 at 09:58

      Hello, i really would like to build the LM13700 version but i cant find any 5 knob version layout

      Delete
  16. hako4 December 2012 at 00:22

    thanks John, i built this today and it worked like a charm except the threshold pot;-(. now i know why.....;-)

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  17. kod2nd4 December 2012 at 08:22

    So anyone dialed in the perfect values for all 5 knob pots yet?

    ReplyDelete
  18. johnk4 December 2012 at 09:05

    the pot values posted are the correct ones.

    ReplyDelete
  19. johnk13 December 2012 at 02:57

    here's a couple pics of mine using Mark's layout with the CA3080 chip. I call it the 'bass comp' since I slightly modded it for more low end. IMO, this is a great sounding and versatile compressor.

    http://johnkvintageguitars.homestead.com/Effects/Compressors/MerlinComp2-01.jpg

    http://johnkvintageguitars.homestead.com/Effects/Compressors/MerlinComp2-02.jpg


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    1. IvIark13 December 2012 at 09:27

      Excellent stuff, thanks for the pics John. I'm about to buy myself one of those Brother labellers as a Christmas present to myself! Providing I can find a decent local source for the tape. The Brother ones seem a lot more common in the US than over here so all the tape sellers I can find on eBay seem to be in the US.

      Delete
    2. mikejoyce13 December 2012 at 13:12

      what did you change to get more low end, john?

      Delete
  20. johnk13 December 2012 at 16:15

    a larger value input coupling cap.

    ReplyDelete
  21. mikejoyce13 December 2012 at 20:45

    That's the 10n on the bottom left, correct?

    ReplyDelete
  22. Unknown8 January 2013 at 08:57

    I've had a go at building this, but so far think I've made a mistake. Here is a thread with the details and voltages:

    http://www.diystompboxes.com/smfforum/index.php?topic=100697.0

    I'm going to have a look at this tonight, so any more thoughts and advice will be well received!

    ReplyDelete
    Replies
    1. IvIark8 January 2013 at 10:29

      As Merlin mentioned, the different voltages on the IC pins and transistor is very peculiar. The base and emitter are connected to pins 1 and 2 of IC2 via a solid track so it can't even be down to a bad joint. Check the link at IC1 pin 5 though. That connects that pin to the collector and if the solder joint isn't good there, that could account for the different measurement.

      Delete
  23. Alltrax7414 January 2013 at 13:36

    From my understanding the 3 extra pots are :
    1M for threshold
    1M fot release
    100k for attack
    Linear pots I guess ?
    Thanks very much

    ReplyDelete
  24. Alessandro28 February 2013 at 01:21

    It would be any major difference between using BC327/25 or BC327/40 or BC327/16?

    ReplyDelete
  25. Alessandro28 February 2013 at 16:19

    This comment has been removed by the author.

    ReplyDelete
  26. DR.K fx junkie26 May 2013 at 18:01

    I've been struggling with this circuit for about 5 hours now, all I'm getting is an extremely fuzzy low fidelity distortion, with no compression whatsoever. Could it be a bad ca3080? Any suggestions would help. Thanks.

    ReplyDelete
    Replies
    1. johnk26 May 2013 at 18:10

      IMO, a bad CA3080 is much less likely than you having an error in your build somewhere. first check for solder bridges, misplaced part(s) or a wiring issue.

      Delete
    2. DR.K fx junkie13 June 2013 at 04:16

      As mind-blowing as it is, it was the CA3080. I finally bought another one, popped it in the socket, and now it works. I thought at first it could be the op amps, I had error checked the board several times and taken voltages, so I used some nice OPA2134s. Now, its a super transparent and hi-fi circuit. I love it.

      Delete
  27. Fede25 July 2013 at 08:45

    John, could you share the layout for the 5 knob LM13700 version? I don't live in the states and it's hard to find a CA3080 for a reasonable price. Thanks a lot to everyone sharing here.

    ReplyDelete
  28. johnk25 July 2013 at 09:30

    This comment has been removed by the author.

    ReplyDelete
    Replies
    1. Fede25 July 2013 at 11:20

      Thank you a lot!

      Delete
    2. Iago25 November 2014 at 04:10

      Wow, someone made a copy of Sabro's layout and gave no credit to the man! That's not nice at all...

      Delete
    3. mirosol25 November 2014 at 15:07

      Sigh. I thought we had this subject settled months ago... Yup. That's not the way to do things.
      +m

      Delete
    4. Iago4 March 2015 at 22:22

      LOL, I found out about that much later, just by chance...

      Delete
  29. jon q2 August 2013 at 23:58

    I built this using a 2n5087, and it 'works' but it doesn't sound like i have a lot of compression even at max and i have to turn the level up all the way for unity gain... is this normal, or a byproduct of using the 2n5087?

    ReplyDelete
    Replies
    1. jon q3 August 2013 at 00:26

      Radio Shack has some 2n3906's so i may go grab a couple and try them out. I built the 2 knob version.

      Delete
  30. Goldenmonkeycolor23 October 2013 at 08:41

    so this doesnt rely on the ca3080 as much as the dynacomps and such? should i save my nos ca3080 metal can guys for other builds?

    ReplyDelete
  31. Json13 August 2014 at 04:47

    anyone know what could be causing a fuzz signal with no compression? I have swapped the CA3080s and the op amps but no change ideas?

    ReplyDelete
    Replies
    1. mirosol13 August 2014 at 09:19

      Sounds like a short on signal path. Or possible wrong resistor value. Knife the gaps and try to probe it to see where the distortion begins.
      +m

      Delete
  32. Json14 August 2014 at 00:33

    I did not find any solder bridges I cleaned between the strips anyways, also found one resistor that was not the correct value, I swapped it out but still have the low fuzz. I do not have a oscilloscope only a multimeter so I have no way to check the signal. Any other recommendations I really want to get this pedal working so any help would be greatly appreciated.

    ReplyDelete
  33. Json14 August 2014 at 01:00

    I'm new to making pedals so I'm hiving a difficult time troubleshooting this here are the pin voltages

    IC1
    1: 8.62
    2: 8.63
    3: 8.62
    4: 9.16
    5: 8.72
    6: 8.77
    7: 9.37
    8: 8.75

    IC 2
    1: 8.15
    2: 8.61
    3: 5.71
    4: 4.15
    5: 7.98
    6: 8.63
    7: 8.63
    8: 9.37

    IC3
    1: 5.71
    2: 8.77
    3: 0.00
    4: 4.28
    5: 4.28
    6: 8.36
    7: 8.73
    8: 9.37

    ReplyDelete
  34. Json14 August 2014 at 02:46

    Found the problem had some jumpers not wired under the IC chips soldered them in and its working! However I will most likely change the values on the resistors listed.

    ReplyDelete
  35. NickLouiz29 February 2016 at 20:24

    I'm planning to built this comp using the LM13700 daughterboard and the three added knobs, but I can't decide which layout should I use...
    The original layout from Mark or the modded John's version (http://johnkvintageguitars.homestead.com/Effects/Compressors/Modded_Marks_5knob_engineers_thumb.png)?
    As far as I can see the Release and the Attack pot mod is very simple in both layouts but what about the threshold pot?
    Thanx in advance!

    ReplyDelete
    Replies
    1. NickLouiz1 March 2016 at 21:23

      Ok...nevermind guys... I just found sabrotone's verified layout with five knobs and the LM13700.
      I'm gonna use it for my built so I don't have to mess around with the daughterboard. Thank you anyways...

      Delete
  36. Unknown5 May 2016 at 12:21

    I just built the 5 knob version, and it sounds great!

    Is possible to modify this to accept sidechain input? How would you go about that?

    ReplyDelete
  37. Piotr Kuzemczak6 May 2017 at 06:03

    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 unpleasent way). Everything double-checked, been building a dozen effects successfully so far.
    How can I decrease the gain of compressed signal?

    ReplyDelete
    Replies
    1. Iago5 June 2017 at 03:26

      I had the same problem with mine. I think I was using 2x TL072CP's and got this crappy sputtery overdrive, and when I tried TL072CN's the effect got clean. So, that would be the first thing I'd try.

      Delete
  38. Clay1 January 2018 at 04:23

    is there a clean blend circuit that will work with this? if not can I throw that in as a request? if this circuit is actually that much better than the dynacomp- wouldnt it be awesome to have this as a full featured 6 knob (or even 7 knob with a tone control) compressor? I guess if the attack, threshold and release work well they would make the clean blend less nescessary than it is on the two knob comps. what do you guys think?

    ReplyDelete
    Replies
    1. Doxasound5 February 2018 at 16:59

      The Ratio is a a blend knob. If you read what he says about the compressor (red text), he mentions the ratio blends the two signals, etc.

      "The ratio control blends compressed and uncompressed signals, so its variable from zero to infinite ratio (limiting)!"

      Delete
    2. Unknown5 March 2018 at 20:13

      I have understand that the ratio control blends compressed and uncompressed signals. However, the addition of an extra blend knob has been done on the Refinery v2 by Foxpedal which is based on the engineer's thumb.
      https://foxpedal.com/products/refinery

      Here, a video in which the difference between the ratio and the blend knob affect the sound:
      https://www.youtube.com/watch?v=X7hpzOuUeJU

      Hope it helps ^^

      Delete
  39. Claudio27 June 2018 at 15:27

    can I replace the 10K form treble swicht with a pot right? It will be useful with tone knob or not?

    ReplyDelete
  40. Unknown11 September 2018 at 00:37

    Hey. Built this a while ago and its great. Only issue I have is that this thing cuts quite a bit of lows. Its ok by itself but throw a tube screamer in the mix and by by bass frequencies. I dont know a whole lot about this circuit but would changing that 10nf input cap to say 100nf or even 470nf, 1uF be sufficient to let enough lows through to use with bass and 7 string guitars?

    ReplyDelete
  41. cacopanda15 November 2019 at 13:46

    Can I run 18V on this?

    ReplyDelete
    Replies
    1. Doxasound15 November 2019 at 18:51

      Datasheet for the CA3080 say's 15v max, so I'd run 12v at most! TL072's are fine @ 15v, too.

      Delete
    2. cacopanda18 November 2019 at 18:01

      What if I were to use LM13700?

      Delete
  42. Unknown8 June 2020 at 05:40

    I've got a problem where theres only a tiny bit of compression. the sweep on the ration knob does nothing, but at the end of the sweep counter-clockwise theres a bit of static noise then it just sound like bypassed signal

    ReplyDelete
    Replies
    1. Unknown8 June 2020 at 05:49

      treble boost switch doesnt seem to have a noticeable effect either. also before the ratio control is fully ccw (that bypassed signal) is very very lightly overdriven tone.

      Delete
  43. Jun d24 January 2021 at 08:08

    Just finished my engrs thumb comp and it works great!LM 13700 ic is no problem at all even thou its fr china!

    ReplyDelete

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