I also played around with this really original fuzz/filter. He reminded me a bit of Big Muff on some psychedelics in some settings and I enjoyed that about him at times.
But what I didn't like about it were the oscillations. So I got into modding and playing around with it. I finally managed to remove them by connecting the 220R from the Zobel network to a real ground (not a virtual one as in the original schematic). Oscillations finally appear to a lesser extent only with the volume on the guitar at minimum and the tone control on the guitar at minimum, that's not bad (In the previous modification in the original scheme, I replaced the 220R with 10k in the Zobel network and this also reduced the oscillation, but it did not disappear).
I also tried setting the zero offset of the opamp with the potentiometer and its effect on the sound. Around 50% it seemed to add a clean sound to the distorted one, it did something but it wasn't as pronounced as I expected.
It's a really sensitive high-gain circuit and filter at the same time, so if the components are not well placed, it can cause problems.
And I also remembered: I put a 1k resistor to ground on the output. For a "room volume setting", it's really too loud
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