[sdiy] monolithic VCO chips for FM??

[john mahoney]

> Well, the potentiometer per note approach would be a necessity if you were
to use
> those VCOs that does not work in pitch so you can tune each note on all
the other
> octaves where double or 1 volt DC increment won't get you double the
frequency.....

Yes, that will work. When Harry speaks, though, it's usually a good idea to
listen. Harry said, "Temperature stability and no long term changes with age
and vibration would make the trimpots a tough choice. Calibration of such a
system could be a nightmare."

Sure, you can tune the trimpots for each note. Without temperature
stability, it's all pointless, though! Regardless, you will still be locked
into each of the pre-tuned pitches -- a tuning knob or octave up/down switch
will be impractical without accurate, expo VCOs. A vibrato CV (FM) will have
a different affect on each note (in some cases, this is okay or even
desirable). Pitch bend will be *very* difficult to control, requiring a
different input on each note to get the same degree of pitch bend.

Since you are just starting in synth DIY, my [only slightly more
experienced] advice is to follow the traditional path before blazing your
own trail. There are many good reasons why you should use
temperature-stable, exponential response VCOs. The ASM VCO is often cited as
an excellent, proven VCO design based on readily available parts (no Curtis
chips or other unobtainium). You can get ASM PC boards from (Mr.) Laurie
Biddulph at http://www.elby-designs.com/.
--
john

P.S. I hate that Oakley trademarked "unobtainium." Bastards!