Median Compressor clipping issue

[bidurgi999]

I built the Median Compressor from PedalPCB. Everything else works fine, but there’s one problem.

When I play chords or pick hard, a crackling noise occurs, as if the signal is clipping. Even when I turn down the trimmer, the noise still happens.

I set the Q2 bias to 1.85V and I’m using an OPA2134.

If I pick lightly or roll down the guitar volume to about 7, the noise disappears.
Does this confirm that it’s definitely a clipping issue?
If so, what would be the best way to fix it?

 

[micmac]

Are you going directly into the compressor with your guitar, or do you run a booster or something in front of it? Active pickups or passive? Can you record the noise so we get a better idea?

 

[bidurgi999]

I used a Gibson bridge humbucker, and there’s a Polytune tuner between the guitar and the compressor.
I’ll attach a sound file as well.
View attachment Untitled.wav

 

[micmac]

Yes, that doesn't sound good. Do you get the same when you turn the Blend knob CCW?

 

[bidurgi999]

네, 좋지 않은 것 같네요. 블렌드 노브를 반시계 방향으로 돌리면 같은 결과가 나오나요?

모든 노브는 12시 방향으로 설정되어 있으며, 블렌드 노브를 조정해도 같은 결과가 나옵니다.
다른 모든 것은 정상적으로 작동합니다. 납땜 문제일 수 있을까요?

 

[micmac]

Could be. Or maybe a broken opamp. If you socketed the opamps that's probably easiest to try. If you have some other opamp lying around, like a TL072, just try it out if replacing any of the OPAs has a positive effect.

Finding a potentially bad soldering joint is trickier. Probably best to step through the circuit with an audio probe first to find where the clipping is introduced.

 

[micmac]

You wrote that it doesn't matter what position the blend knob is in. Then I reckon the problem should be somewhere around the input or the output.

 

[bidurgi999]

Could be. Or maybe a broken opamp. If you socketed the opamps that's probably easiest to try. If you have some other opamp lying around, like a TL072, just try it out if replacing any of the OPAs has a positive effect.

Finding a potentially bad soldering joint is trickier. Probably best to step through the circuit with an audio probe first to find where the clipping is introduced.

Since the same problem occurs even after replacing the op-amp, I guess I’ll have to look for another solution.

Thank you for your kind response. Have a great day!

 

[micmac]

No problem, great day to you, too!

 

[Hirti]

I also built one recently, also biased it to 1.857V. With single coils everything is fine but with humbuckers I also get clipping (depending on how high the attack knob is set)

 

[micmac]

The same clipping that bidurgi999 documented in the attached recording? If not probably best to open a new topic if needed.

 

[Hirti]

Yes, the same clipping.

 

[micmac]

Good to know, thanks.

Yesterday evening I replaced the four OPA1678 opamps in my Median with four TL072. I wanted to see if with a simple opamp-change I could reproduce the clipping noise from the recording. I tried with two different humbucker guitars, also switched the buffer on the tuner in front on and off. I couldn't get the pedal to clip, it was fine.

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