I got a PM from a member concerning a one-off I had made for a former manager in my organization. Unfortunately, this member's inbox is full so I can't send the PM, but figured the info was useful for other folks here.
The Karate Shop project, over at the Madbean site, is a clone of the old Systech Harmonic Energizer. The HE is a kind of resonant booster, not too far removed from the old Anderton Frequency Booster, except with variable frequency and bandwidth/Q/emphasis. It was purportedly used by Frank Zappa to achieve assorted "fixed wah" sounds.
The nice thing about the KS/HE is that it has a sort of "uncommitted" op-amp gain recovery stage that can be put to good use. As shown, it uses a 50k pot in the feedback resistance path of a non-inverting gain stage, just ahead of the output. Does that pot need to be 50k? Nah. Let's make it 250k, to give us a potential max gain of 251x in that stage. If we stick a back-to-back pair of diodes in parallel with the pot, we basically have a Tube Screamer with a variable resonant boost before the clipping stage.
I wired up mine to switch between normal functioning and clipping use. A wire goes from one end of the pot (let's say the output end) to the common of a SPDT toggle. One outside lug of the toggle has a set of clipping diodes of your choice, and the other has a 68k fixed resistor. The free end of the resistor and the didoes are tied together, and you run a wire from there to the other side of the 250k pot. In the one toggle position, you have the clipping diodes, and in the other you have a 68k resistance in parallel with the pot to drop it down to a max resistance of 53k, - within 10% of the original pot value.
And there you go. The HE was useful on its own. Now we have a pedal than can double as a fixed wah PLUS overdrive. There is a 1M terminating resistor on the output. If you want to have independent control of both drive and output level, feel free to make that 1M fixed resistor a 1M audio pot. And if you use the buffered output, don't forget to stick a 1M terminating resistor on it to prevent switch-popping.
Cool idea! Thanks for sharing!!!