noisy mcmeat

[incal]

happy new year everybody
After 2 days of tinkering and debugging i finally made my new mcmeat to work. The only problem is that if i hit the strings hard the pedal gets very very noisy. If i'm gentle to the strings the mcmeat works great. Has anyone any ideas on this?

[Mike Burgundy]

What exactly does the noise sound like? Hiss? Crackle unrelated to the music? Distortion?
Your descreption suggests distortion, in which case there might be a wrong value resistor in a feedbackloop or something.

[incal]

it's a higly distorted sound. I have checked all resistors and capacitors again and again and they are OK

[swt]

i've had the same problem. it's probably a bad ic. change the tl074 and the problem will be solved. At least that happened in mine.

[incal]

Actually this morning i did something different.I changed the R1 from 1,5k to 120k. And guess what, i think it worked. I'm not really sure if this small change had any effect in the pedal besides reducing the noise, i didn't have time to check.Any opinions on this.

[Mike Burgundy]

that would massively decrease the signal seen by the first opamp. Unless there's something wrong in the gain structure, the pedal will now not be unity at all. If it's is close to unity gain, closely scrutinise all resistors in the audio path. There's bound to either be a series one that's waay too low, or a feedback loop one thats waay too high.
If it's NOT close to unity (too low), the circuit cannot handle the levels that it should, and then chip might be a suspect. Plugging another one in there is always a good idea.