[sdiy] VCO reference voltages

[David G. Dixon]

> > Just my own experience.  Every time I've ever measured my rails, they've
> > always been within 1 mV of the last time I measured them.
> 
> Yes, but I think you might be one of the few people who understand
> it's quite useful to have a good PSU :-)

Aha!  And that means that those who don't understand the importance of
having a good PSU will never appreciate the subtle benefits of having
regulated rails on their tuning pots!  Ergo, there's no problem!

(My logical kung fu is too strong!)

> > It's just what I started out doing, and I've seen no reason to change
> it.
> 
> Gotcha. Inertia is as good a reason to do things as any :-)

It's not (all) inertia.  In most cases I'm just trying to learn by looking
at other people's circuits, and I don't necessarily know enough about it to
question some of the things I see.

For example, before I asked my question yesterday about regulating rails
(which largely arose because I was trying to gauge just how seriously I
should take Ian Fritz's admirable perfectionism to heart), I had a quick
look at quite a few VCO schematics on the web.  Nearly all of them show the
tuning pots connected directly to the rails, including the Thomas Henry
VCO-1s I built last year.  Nowhere on Scott Stites' site did he or Thomas
Henry bother to mention that this was potentially a problem or a compromise,
or suggest that one should really rather use regulated voltages for these
pots.  Ditto Ray Wilson.  And Ken Stone.  And Rene Schmitz.  And Gene Stopp
and Magnus Danielson.  And Jurgen Haible.  And, and, and...

The question really arose not because I think that this is such a big
problem, but mostly because there was no way for me to "look under the hood"
of the commercial units (Synthtech, Modcan, dotcom, et al.) to see what they
typically do, because their schematics are unavailable for scrutiny.  In
fact, if anyone here owns any of these and would care to share this info
with me, I'd be very interested to know.