[sdiy] VCO reference voltages

[Magnus Danielson]

David,

>>> 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...

Didn't know I was such an authority...

Ehm well. Fixing the tuning pots is possible, but be aware that you want 
your +15 V (or what ever) mirrored to -15 V (see Oberheim SEM) rather 
than individually controlled. Also, it comes to no great use unless your 
sources also has stability treatment. It becomes an endless hunt for 
precision. Consider the good enought argument.

Maybe isolation of noise-makers is needed. Star-feed/ground or even 
separate supplies.

Cheers,
Magnus