[sdiy] 2164 Expo VCO tracking

[David G. Dixon]

> David,
> that's great news!

Thanks!

> so what's the reason it worked on the breadboard?

No idea!

> Where is that filter located?

It's just a 100pF cap from the comparator output/JFET gate (same trace) to
ground.  It is essential.  100pF may be slightly too large, but 47pF is too
small and 120pF is definitely too large.  I'm going to get some inbetween
values today to try, but 100pF works.

> 18 octaves is more than you'd ever want, I think. I've never composed
> a synth part which spanned 18 octaves.

I agree.  However, the tradeoff is in good audio tracking up to or slightly
beyond the top of the audio range vs. the option for long LFO periods at the
bottom.

> Well done! :-) Now it's time to think about features on the PCB.

What sort of features?