technology of... the octavia?

[Luke]

hello guys,
is there a 'technology of' type text on the ocavtia?  (or any octave up generating design?) I am trying to find out the 'hows' and 'whys' octavias work, and how to mod them. Anyone have any ideas where I can find more info?
THanks guys,
Luke

[R.G.]

All commercial octave up pedals that are analog based are at their heart full wave rectifiers. That is, one polarity of the incoming waveform is folded over to go the same direction as the other polarity. This is a brute force way to make something happen twice as often as it does in the incoming waveform, and it generates a lot of hash/distortion, but it does make a highly audible octave up sound.

The TychoBrahe Octavia does this by driving a transformer with the input signal, then using diodes to full wave rectify the signal, just like a power supply does. The Roger Meyer Octavia, the Fender Blender, the Foxx Tone Machine and the Green Ringer do it by electronically making an inverted signal then using diodes to rectify, replacing the Tycho transformer with transistors. The Univox SuperFuzz and its 57 clones all use a "differential transistor" cell to full wave rectify with gain.

The only analog octave up that doesn't do full wave rectification is my MOS Doubler. That one uses the second order distortion of MOSFETs to generate the octave, then cancels the non-distortion signal in a differential cell. It looks similar to the bipolar transistor FWR cell, but works differently because of the MOSFET physics.

Digital techniques can actually make a true, distortionless octave up, but then ... they're (ugh) digital.

[JohnM]

...electronically making an inverted signal...

Could you explain that a little?  Why does the inverted signal have to be created?  Why isn't it already there in the bottom half of the sine wave ready to be "folded over"?  Thanks.  -John

[Doug B.]

is there a 'technology of' type text on the ocavtia?  (or any octave up generating design?) I am trying to find out the 'hows' and 'whys' octavias work, and how to mod them. Anyone have any ideas where I can find more info?

Here's some relevant info:

 http://www.geocities.com/SunsetStrip/Studio/2987/octave.html

- Doug B.

[Luke]

Thank you, thank you, thank you guys  
This is EXACTLY the info I was after. Thanks for the link Doug, and thanks RG for the great indepth answer. I think i undersatnd the OCatvia a bit more.
Thanks again guys,
Cheers,
Luke