SOLVED Keepressor (Keeley Compressor clone) barely compresses

[neiltheseal]

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 https://pcbguitarmania.com/wp-content/uploads/2021/12/Keepressor-Building-Docs-1.pdf).

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 audio 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 the disappears
Q3 - signal fine on the base, distorted and metallic signal on collector but consistent
Q5 - signal on base for a moment before disappearing, distorted and metallic, but consistent signal on collector
R20 - signal disappears after a moment
R21 - signal fine on one end (connected to pin 3 volume), but on the other 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 fixed 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 noticeable. Not like the dyna comp which is very in your face at high 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.

 

[neiltheseal]

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

Does anybody have an Idea how I might investigate this further or resolve the issue? I assume it's something to do with not enough power getting to q3 and 5.

Q1

• E - 1.71
• B - 1.38
• C - 8.58

Q2

• E - 1.82
• B - 1.99
• C - 7.45

Q3

• E - 0
• B - .07
• C- 9.1

Q4

• E - 8.45
• B - 8.95
• C - 9.07

Q5

• E - 0
• B - 0
• C - 8.95

IC

• 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

 

[neiltheseal]

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?

 

[neiltheseal]

ISSUE SOLVED

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 am quite happy with it. I might have to do a build report.

 

[ThatDude]

Hi @neiltheseal. I am building a Keepressor currently. Can you confirm that I am understanding the C5 issue correctly? I need to have the capacitor from C5 run to the emitter instead of it going into the other hole for C5? Thanks in advance.

 

[neiltheseal]

Hi @neiltheseal. I am building a Keepressor currently. Can you confirm that I am understanding the C5 issue correctly? I need to have the capacitor from C5 run to the emitter instead of it going into the other hole for C5? Thanks in advance.

Yep that's right. Basically one leg of c5 (that is connected to c6, r7 and lug 1 of clip pot) is soldered in as usual. This is on left side of my first picture. The second leg of c5 should be connected to emitter of q1 directly below it. Don't solder in the hole here as it is not connected to the emitter. Instead grab the free leg of that capacitor and solder it to the emitter of q1 manually.

This is a great compressor when it works.

 

[ThatDude]

Yep that's right. Basically one leg of c5 (that is connected to c6, r7 and lug 1 of clip pot) is soldered in as usual. This is on left side of my first picture. The second leg of c5 should be connected to emitter of q1 directly below it. Don't solder in the hole here as it is not connected to the emitter. Instead grab the free leg of that capacitor and solder it to the emitter of q1 manually.

This is a great compressor when it works.

Thanks so much for confirming! I am looking forward to hearing it.

 

[Quiddel]

Just wanted to add a possible source for mistakes, as I stumbled upon this thread troubleshooting my Keepressor. I managed to put in Q2 upside down, as it's the only transistor with the "belly down". Maybe it helps someone with the same issue. Nice project, by the way!