[sdiy] Temperature stable lin-exp converter with a CA3086 or CA3046

[John Blacet]

The whole "how stable should it be" regarding VCOs is an interesting
discussion. On the one hand, you don't want absolute lock-step digital
stability in an analog oscillator, as being just a bit drifty makes them
sonically much more interesting to use. But, you don't want to be
reaching for the Fine Tune knob more than a few times a session; that
gets annoying.

The whole technology limitations of analog guarantee that absolute
stability is really unobtainable, but you can get close enough to make
nice analog VCOs. The best commercial VCOs go a bit beyond the customary
temp comp resistor approach with techniques to "mop up" residual drift.
Some synths of old, for example seem to auto tune via uP on a periodic
basis.

I wonder about a PIC based processor in a correction loop? Say, just a
nudge now and agian to make the CV to freq ratio stay "close". You could
even program in bits of subtle "misbehaviour".

Regards,
-----------------------------
John Blacet
Blacet Research
http://www.blacet.com