Nice little mod - Madbean Karate Shop

[Mark Hammer]

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.

[jrod]

Cool idea! Thanks for sharing!!!