[sdiy] 2164 Expo VCO tracking

[David G. Dixon]

> Wow, that's really good performance for an OTA-based circuit!  You've got
> a real winner here.

Thanks, Ian!  Coming from you, that means a lot.

I forgot to mention it before, but I think that increasing the cap size also
helped circuit performance, over and above increasing the 0V frequency.
Anything which makes the JFET current injection pulses smaller relative to
the ramp current has a positive impact.