Another case of redraw = insight

[Mark Hammer]

I was looking at the BYOC site - specifically at the PDF for the "Divided Octave" - and noticed something I had never realized before when looking at existing drawings: the Mu-tron Octave Divider also has an octave up.  Moreover, one can leave out a great deal of the circuitry and have a clean + octave-up variable blend if you want, requiring only a dual op-amp and 2 transistors.

While obviously feasible by modifying virtually any octave-up fuzz, octave amount is generally either all-or-none or continent on drive level in the majority of octave-up units.  The Mutron drawing provides a clear vision of how to implement a continuously blendable clean+octave.  Nice!  I may have to whip this one up.  Not that I have anything against octave-down; I'm just curious about what a variable octave-up would sound like.

[deadastronaut]

would it only be octave up on the higher frets still though...?

[Mark Hammer]

would it only be octave up on the higher frets still though...?

Since it is the same family of circuit as the Foxx Tone Machine, Fender Blender, Superfuzz, and Green Ringer, yes.   However, what the op-amp input stage allows you to do is shape the signal fed to the phase-splitter so that the octave comes a little easier and is a little more discernible.  That's one of the things the Foxx does well with its input stage.  Part of that is also matching the levels of the two complementary signals produced by the phase-splitting so that when the number of peaks at the fundamental frequency are doubled, you hear it as an octave because those peaks have a consistent amplitude relative to each other (obviously their overall amplitude declines as the note dies out).  You may have seen trimpots on Superfuzz and Green Ringer drawings for precisely that purpose.

Apart from that, it's not the circuit so much as the properties of the string at different points along the fretboard.  Strings get stiffer, the higher up you fret.  And stiff strings get you mostly fundamental with much less harmonic content, and noticeably less pitch fluctuation (assuming you can suppress your finger vibrato instincts).  It is the doubling of the fundamental for a long-enough period, in the absence of a bunch of distracting insect noises from doubled harmonics, that makes for more explicit octaving.  One might extrapolate from this that thinner gauge strings don't get obvious octaving until somewhat higher up the fretboard than heavier gauge strings.  (That assumes one isn't doing an SRV thing and using heavier strings tuned down for more slack.  If you have any direct experience with that to either corroborate or refute, I'd be very interested.)

The original schematic for the Mu-tron Octave Divider doesn't really convey that it includes an octave-up.  Instead, it provides a "Ringer" switch to turn the octave-up on or off.  It wasn't until I recognized the circuit and started looking through the service manual that I saw a rather non-obvious mention of octave up.  While it is certainly true that all of the octave fuzzes noted here give a kind of ring-modulator sideband sound when you bend notes in a certain way, they aren't formally ring modulators as such, despite what Dan Armstrong called his octave-fuzz!