Help debugging Thor

[spi]

Hi, I have built a Runoffgrove Thor using the tagboardeffects layout (https://tagboardeffects.blogspot.com/2013/01/runoffgroove-thor.html)

I'm getting high pitched squealing most of the time.  I've been using an audio probe to determine where the signal goes bad.   

Referring to the schematic here, http://www.runoffgroove.com/thor.html, everything sounds good until it gets to the gain pot.
With the bright switch off, Lug 3 sounds ok, but Lug 2 has the squealies.   With the bright switch on, both Lug 2 and 3 get the squealies.

So I thought the issue might be coming from Q2.  However, this is where I get confused.  If I pull out either Q3 or Q4, then the signal through the gain pot, and at the gate and drain of Q2 sound good. At Q2s drain there's a strong overdriven sound without any squeals, which is what I expect.

So now I think that the issue must be coming from the minibooster part of Q3+Q4.  I tried swapping in some other transistors in case they are bad, but none of the replacements help.  I don't think all my jfets are bad (slightly out of spec maybe but they behave like jfets).

I'm not sure what the next step to try debugging.  Anyone experience something like this before?

[bluebunny]

Lead dress?  Try shielded input and output cables?

[Vivek]

Have you tried to add some extra capacitors that reduce the high frequency gain of each stage ?

[spi]

Thanks for the responses so far.

I put this on the shelf for a while, but might try to get it going again this weekend.  I'll take a close look at the leads, as I am wondering if I got good connections between the pots and switch.