Noisy P100 Debug Question

[A.J.]

Hi All;

I've had a P100 (from GGG layout) sitting on my desk for a couple of weeks - good phase sound but some bleedthrough/noise was present - I figured that this would be gone when it was boxed up, which is what happened. Good.  Except that now I've realized that positions 1 and 3 on the 4-way switch (yup, used that instead of a pot for regen or depth - I tried a couple of different set ups but ended up finding that stock was fine) are really noisy/hissy - these are the settings without any regen.  The regen positions sound fine.

I'll qualify fine - there's a certain amount of overall noise, but certainly normal - I'm going to play with adding some caps to cut this down and maybe tweak the feedback resistor at the input for more gain, then reduce the output to compensate.

I added a 150K resistor to the switch to add that in series with the regen resistor and this seemed to quiet it down and sound generally the same as the connection being open (no regen) - it gets noisier as this resistor value is increased.  Curious, and I can't quite figure out why - expecting that this isn't normal....I would expect the feedback channels to be noisier....

The circuit is stock - used TL082s and had to use 24K for the regen resistor to avoid squealing.

Any thoughts?

A.J.

[axg20202]

How are you powering it? Sorry, had to ask. As you probably know, PSUs are a common source of noise issues. Try battery power to rule this out.

[A.J.]

I've got it on a battery.

Curious - really hissy with no regen selected, quiet with it selected.  Everything seems grounded properly, checked the traces......

A.J.

[axg20202]

Is the battery new? I think the P100 is a fairly hungry circuit with all those ICs etc - maybe a weak battery could cause noise? Just thinking out loud here. Only other thing I can think of is perhaps one of your ICs is faulty. Do you have another circuit handy e.g. a disto box, that could use this IC? Swapping each IC into another working circuit could help to eliminate these

[A.J.]

Well - I swapped out the ICs - that didn't change anything - then I put 1n5 caps in parallel with both R11 and R20 - the feedback resistors at the end of the phase stages as suggested by (I think) moosapotamus in an old thread - bingo! - almost completely noise free.  I mean, I can crank my amp up and switch the pedal on and off with almost no noticeable change.  With my strat switched to pos 2 and 4 it's nearly dead silent.  Don't notice too much of a tone change, either.

I took turns with the caps in and out and found that it really only needed the one on R11 to solve the problem.

Anyway - sounds good - will stop tinkering before I bugger it up.

Oh - at higher volume there was an annoying oscillation - had to increase the regen resistor to 33K.

A.J.