a couple mods to this circuit that someone may find useful.
first, on the underside of the board, solder on two wires to the two solder points for r11, leave r11 on the board. run the wire from the topside of r11 to a 560r resistor to pin 3 of a b25k pot. connect the low side of r11 to pins 1 and 2 of the pot.
now ya can scoop the midrange, or boost it, or have the stock muff tone. works freekin great. doesn’t have as much effect when the tone knob is cranked full treble, but it lets you really get on top of the tone spectrum. full up is a boosted mid, about 1:00 is stock, or you can scoop it right down to spam-suckin trailer trash tone. very useful, and really lets the stock circuit come alive.
i tried every opamp i had, and my fave was an lm358p for u1 and a tl062 for u2.
i was having a problem with “ringing” and a bit of oscillation, even with the knobs all off.
i discovered a 1n cap between pins 4 and 5 of u1 obliterated the ringing without fucking up the tone, distortion, or volume.
so if anyone has a problem like that, that’s a qnd cure.
ps, a real nice clipper for this circuit is an 1n914 in series with a pink led <they have a real high forward voltage n a LOT of compression and finally an 1n34 ge.