[sdiy] "Load" on power supply changes pitch of VCO...

[Mike Beauchamp]

The first VCO I built was Thomas Henry's XR-2206 VCO
(http://mypeoplepc.com/members/scottnoanh/birthofasynth/id20.html).

I'm noticing that when I experiment and add various things, the pitch
changes. It's as though the pitch is dependent on how much current I'm
drawing from the power supply.

Is this one of those "that's analog synths for ya" type problems like
I think? Where me adding more parallel resistance (therefore less
overall resistance) between V+ and gnd (or gnd and V-) is affecting
the voltage at the wiper of the "coarse tune" and "fine tune"
potentiometers (which are wired to V+ and V- at each end), and
something that should be expected? Or is there something obvious I'm
overlooking.

For example, if I decide to add LED's to indicate certain settings
being on or off, when the LED is switched on, the pitch of the VCO
will drop audibly and require retuning. If the answer is "that's why
you don't see LED's on VCO's" or something, feel free to hit me over
the head with a large trout. But if one was to build a whole modular
system powered off of a shared powersupply, if one module varied it's
current draw, wouldn't that really bugger up things?

Anyways, thanks again in advance.

Mike