Octave

[Daisycutter]

whats makes a fuzz octave?

is an overtone separated from the main signal and boosted then or something?

[Elektrojänis]

Most octave up fuzzes work by full wave rectifying the signal. Check out the guitar effects FAQ at www.geofex.com.

[Mark Hammer]

If you feed a stable signal into a scope, you will see an upward and downward portion of the waveform, right?  The upward portion is "up" relative to some zero point in the middle.  Same thing with the downward portion.

Most forms of octave fuzzing take one side of that zero/middle, and flip it over electronically. so that instead of going, say, "down" it goes "up".  What you have now, is two "bumps" where you used to have a big bump and a furrow/trough.  Since you have two "bumps" in the space formerly taken up by one, you have doubled the frequency of bumps.

The "folding over" of a rising/falling signal that fluctuates above and below a zero point into a signal that ONLY rises above the zero point is called "rectification".  It is exactly what is involved in taking AC from the wallwart (which goes positive-negative-pos-neg-etc) and turning it into DC (which goes pos only).

Typically, the doubling of frequency in this manner is achieved by use of diodes in a way that introduces substantial distortion.  Indeed, getting a NON-fuzz octave by simple analog means is pretty hard to do (though some designs, like those RG Keen has posted, come very very close).

The rectification doesn't really care about overtones as such.  IT takes *everything* "below the middle" and makes it part of the "top".  Since the lower order harmonics are generally louder than higher ones, if the balance between the two "folded-over" signal halves is set right, a string octave will be heard.  In some respects it helps to have appropriate filtering prior to rectification, so that , once the signal is rectified, the lowest order harmonics will be easily heard amidst all the other cacophony that occurs when EVERYTHING is doubled.

[DDD]

In my opinion the FET doubler by R.G. Keen is fantastically good-sounding device, especially if overdriven heavily.

[petemoore]

I hope to be trying out the PUsh Me Pull You quite soon...I'm about to see what it sounds like with a guitar input source, has a healthy, funny buzz when I grab the input wire, going to get the guitar now...