https://www.diystompboxes.com/smfforum/index.php?topic=106243.0
Added more mods from Wampler’s books. Just interested in the crazy effects. Definitely can add a momentary switch to Wampler’s octave synth since it’s only one. Also there is a tremolo mod I can try but the video’s online had a lot of popping noise.

Looks like S1 is the same as Wampler’s Synth Octave hack (C4 jumped to C9, transistor booster to right before clipping diodes). The S1 goes to R16 (tone level) which might be related to the tremolo hack in Wampler’s book, that can connect to S3, that connects to C10, which is the end of the OP-Amp Gain Stage.