octave

[Mikko Helin]

> Does anyone know of a site that either has schematics or block diagrams or
> something that would clue me in on how to build a device that could raise
> an analog signal a couple octaves higher?
> -mark wagy
> 

>We could also do this with a saw wave, we need comparators for the
>0,25,50 and 75% time of the saw and then a polarity switch, that
>"folds" the saw at the respective points of time. Now the signal will
>have some leaps, so we have to add some of the comparator pulse output
>voltage and voila: a tri wave with double frequency.

Simplest way (which I know) to get an octave for a saw wave is to
first use an inverting comparator which outputs (assumption is
that saw wave is +/- 5V ,10V p-p) -5V for signal above zero,
and 0V for signal below zero. Then this 0 - -5V square wave is summed
with the original saw, the result being an octave higher saw wave.
Then add another stage to go another octave up, and so on.

Another way, for sine waves, is to use the square function properties of 
the differential MOS FET pair. There's some discussion on it on Ampage 
(www.firebottle.com/ampage, look at the FX General & FX DIY parts).
You'll also find the schematics of MOS doubler at 

http://www.eden.com/~keen/md.gif

R.G. has used to read this synth-diy mailing list also, so he may 
tell us more about how his MOS doubler works.

-Mikko