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Help with Keepressor (PCBGM)

Started by neiltheseal, May 04, 2023, 07:57:52 AM

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Hello again, I'm back with another issue that I'm struggling with. Can anyone help please?

I recently built the Keepressor (Keely compressor from PCB Guitar Mania). (build docs

The pedal "works" but not like I had expected. I built a dyna comp which compresses like I expect it to. This Keepressor is very subtle

With an audio probe I have found something that might be an issue, although Im not sure what do do about this.

The signal seems pretty strong up to the base of q3. When I touch many of the parts after this I get signal for an instant which disappears.

D3 - the signal is fine on the cathode.
D4 - signal for a moment on the cathode
Q3 - signal fine on the base, distorted and metallic signal on collector
Q5 - signal on base for a moment, distorted and metallic, but consistent signal on collector
R20 - signal disappears
R21 - Signal fine on one end (connected to pin 3 volume), but on the ohter side same problem as above.
C12 and C13 - Signal disappears

I have checked all of the parts (twice) and they are correct. Transistors and capacitors are oriented correctly.

I had the c5 issue mentioned in the build docs but have fixe this. Once fixed the pedal now works and definitely compresses. The issue is that it is really subtle and most knobs don't audibly do that much.

The pedal sounds ok, but it's a bit of a waste of a compressor at the moment as it is barely noticable. Not like the dyna comp which is very in your face at hight settings.

VOLUME: At full volume the pedal is about unity volume.
ATTACK: turned fully CCW has a mild overdrive sound, that I quite like. Compresses slightly more CCW.
SUSTAIN: seems to work like the sensitivity on a Dyna comp, although it only compresses about 1/4 of a Dyna comp
CLIP: I have no idea what clip does, except for a mild volume boost.



I took some voltages and this seems to confirm that the problem is around q3-q5


  • E - 1.71
  • B - 1.38
  • C - 8.58


  • E - 1.82
  • B - 1.99
  • C - 7.45


  • E - 0
  • B - .07
  • C- 9.1


  • E - 8.45
  • B - 8.95
  • C - 9.07


  • E - 0
  • B - 0
  • C - 8.95


  • 1 - 1.3
  • 2 - .07
  • 3- 4.71
  • 4 - 4.71
  • 5 - 1.95
  • 6 - 0
  • 7 - 0
  • 8 - .04
  • 9 - .02
  • 10 - 0
  • 11 - 8.96
  • 12 .07
  • 13 - 0
  • 14 - 0
  • 15 - .09
  • 16 - .07


I've continued trying to find the source of the problem. I did some continuity testing around the problem area, but it seems there is continuity everywhere there should be.

Here is a picture, yellow indicates continuity (please ignore my hand written notes).

Since everything is connected, would the issue be a faulty part? It seems to me there is too much voltage around q4 and not enough around q3-5. I'm guessing there is an issue preventing the voltage from q4 from getting to q3 and q5. Does anyone know why this might be?



After all of my trouble shooting, I plugged the pedal in to see if one of my half-baked ideas would work...and the pedal worked as it should.

My half-baked idea was not the fix, I think it may have been a glob of solder I dislodged while continuity testing.

Anyway, I got it going and an quite happy with it. I might have to do a build report.