[sdiy] Triangle wave octave generation (frequency doubling)

[JH.]

> I achieved something like this with a sawtooth in my modified Jen SX1000. 
> In my case I watch the rising sawtooth with a comparator, and when it 
> reaches a set level I force a reset. There's also a matching variable gain 
> amplifier to compensate for the reduction in amplitude.

With *saw* waves, it may be easier to start with the highest octave, and 
derive the lower octaves from that.
It's the old Korg trick: Create highest saw and pulse, then divide down the 
pulse with flipflops, build a staircase wave from the divided pulses, and 
then fill the steps of the staircase with the saw from the highest octave. 
That way, you get saw waves for every octave just with flipflops and 
weighted summing.

I have used it in my JH-720 VCOs, which are more or less copied from the 
Korg 700 and 800DV:

http://www.jhaible.de/jh_720_vco_core.gif

JH.