I built the Fat Piggy, but find the gain so over the top that the pedal just oscillates.
I'm wondering if R7 should be 68k instead of 680k. I just changed R7 and with 68k it sounds much better.
EDIT:
Also R10 could be lower. I went to 47k for R10.
The Gain-pot should also be lower, IMHO, like...