5K gain pot squeals at max

[ItZaLLgOOd]

I built a Multi-Face from ROG and all is well as long as I don't max out the 5k linear gain pot.  I also breadboarded a Big Daddy and it did the same.  The BDaddy called for a 1k so I thought that was the problem.  But the M-Face called for a 5k.  Is this a sign of a bad pot?? Maybe I need an audio pot?  Thanks

john

[petemoore]

  That circuit can have sufficient gain to cause self oscillation, N/P.
  Try gain reductions, the circuit can be tuned to a wide variety of FF's, some of the settings [esp w/high gain transistors] can easily get it to squeal.

[foxfire]

you can also try twisting the your leads around themselves to help cancel out and crosstalk. it may or may not help but, it usually doesn't ever hurt.

[ItZaLLgOOd]

I forgot to mention that I used 2 2N5088's for the transistors.  So maybe to much gain is the issue?  I'm still learning but is it less resistance less gain or the other way around?  Maybe back off the 100k feedback resistor.

[petemoore]

I forgot to mention that I used 2 2N5088's for the transistors.
  Mongo Gain for typical FF circuit.
  Q1 could be say 70-150hfe and Q2 could be same or more, those have something like 500hfe.
  So maybe to much gain is the issue? 
  Back off the gain pot and guitar volume, but yea, it'll clean up more at guitar with low gain Q's in it.
  I'm still learning but is it less resistance less gain or the other way around? 
  Maybe back off the 100k feedback resistor.
  Maybe, I'd try the other gain altering techniques first unless it's easy to parallel a resistor to the resistor there to reduce it's value, might be able to clip say a 500k pot across it?..then you could see what values about 80k and less do to adjust the sound. 100k is cool.
 

[ItZaLLgOOd]

I also added some hard clipping diodes but the squeal was present before.  The circuit sounds great as long as I don't turn the gain to the max.  If I back off about 1/16 of a turn it's fine.  The pedal will work but for the sake of learning I would like to be able to peg the gain with no ill effect.

I tried a 2n3904 in q1 with the same result.  Those are the only transistors that I have handy.  I'll order some different trannies with my next big order.

Thanks for the suggestions

john