Simple mode addition for Prescription Electronics COB

[Mark Hammer]

A local guy asked if I could make him a clone of the PEI Clean Octave Blend, and it turned out to be a very easy build and pleasing result.  I was pleasing enough that I thought I'd make one for myself.  To be clear, it does NOT offer a "clean octave" that can be blended in.  Rather, it can blend between a clean signal and an octave fuzz.  The octave itself is fairly reminiscent of the Foxx Tone Machine.

In staring at the schematic, I saw how it reminded me of the FTM for some fairly clear reasons - namely the manner in which the octave is obtained.  It employs the standard phase-splitter, but simply combines the half-wave rectified copies of the signal.  The Foxx also does this, but includes a footswitch that can either lift OR connect one of those half-wave copies.  Connected gets you the octave up, and lifted gets you a fuzz, albeit with some added crossover distortion.

I cut a trace on the COB board, drilled two holes and wired up a toggle to make/break the connection for the diode coming off the emitter side of the phase splitter.  Worked like a charm, delivering a pleasing fuzzy at-pitch grunt that could be blended with clean signal.  A mod well worth doing.

[antonis]

I made the same mod on a Fender Blender clone and I can verify Mark's statement..

[Mark Hammer]

I'll note that, when I made a Tone Machine for myself, I would bridge the remaining diode for the "non-octave" mode, since the diode that half-wave rectifies the output of the collector will introduce elimination of a half cycle.  A SPDT toggle or stompswitch can connect the emitter diode in one position, or lift that connection and bridge the collector diode in the other position, to get a fuzz sound with both half cycles.

[pedalbob]

 Thank-you so much for all of the replies.  As always I learn something from the experts when I post a question here.  Hoping I can reciprocate somehow eventually but I am still a humble neophyte at the DIY pedals ... but I became addicted as something to do during covid ...
Thanks for the schematic too !  I had found some tagboard/vero board layouts but none were exact looking at the real thing ... this will save me a bunch of time ...
Thanks again guys !!

[Mark Hammer]

It took me some 45 years to learn how to identify such mods, Bob.  But much of that time precedes the wealth of information and resources readily available to the beginner these days.  Your progress will be MUCH faster than mine.