Super Mod BIG MUFF PI - the mods are all labeled. . . .Red Channel stock BIG MUFF, except that the two CLIPPING STAGES are selectable- Stock is 2way Silicon diodes, in both stages  (switches down)- center position is no clip for that stage....UP on the left is one Si and a red  LED,  UP on the right  is an LED, and Si series pair.......many different clip characteristics there.......it makes a big difference from side to side,  what  you square the signal with...............

the Green Channel by passes the tone stage of the stock muff, which (in most useful position) rolls off almost all the BASS from the signal........ bypassing  almost leaves TOO much behind, but  separate VOL and Gain allows for some adjustment, and results in a second channel (also clipped as set) of "cleaner" Bass Boost .   

HOME
The Third Stage (and final stomp switch) is an internal FEEDBACK LOOP that trickles some of the OUTPUT signal (How much is adjusted with the Pot mounted on the front for ease of Twiddle from standing position) back to the INPUT resulting in Glitchy interaction between the note you are playing, and the "tone" generated by the loop......

The feed back eye can have light flashed over it to jerk the amount of feed back quickly up (light on) and back down again, or in the right lighting, the opposite achived by covering it with your foot....if you stop feeding signal ( by removing cord from guitar) and fiddle with knobs and clip switches, (and a lighter?!?) one can "play" the OSCILLATION like a sort of FUZZED UP synth...... fun fun!

See MR. GREEN for further "refinements" to the MUFF.

Adjusting those two Trim pots effects the over all tone as well ("stock" was 10k if memory serves)