[sdiy] Diagnosis Help Please

[harry]

Hi Mark....

It sounds like you are getting power supply ripple... an AC signal that is
riding on the +/- DC supplies.  This usually means that the supply is
inadequate
in some way... like

Too small (uF) filter capacitors...
Voltage too low before the regulators (the supply IS regulated... isn't it
:^)
Too much current draw is reducing the voltage to where the regulators no
longer work... etc...

The offensive frequency will usually be 60Hz or 120Hz... and will be a sort
of sawtooth wave.  Look at the supplies using a scope set to AC coupling and

crank up the scope input gain... If your supply is good you see a straight
line...
if bad you will see the ripple.

No scope... try measuring the DC supplies with your meter set to AC...

H^) harry

Mark Melvin wrote:

> Hi all-
>
> First of all, let me say that I'm still new at this
> stuff... so be patient with my ignorance.
>
> I'm almost finished with my first synth project and
> almost everything is working... and what isn't working
> I believe I can fix.
> HOWEVER, I have this annoying feature that I hadn't
> planned on incuding.  Perhaps if I describe what I am
> hearing someone could make a guess as to what is
> happening.
>
> What I am experiencing is best bescribed as "beating"
> in the VCO.  To me it seems like there is a signal
> that has bled into the VCO.  It seems to be constant.
> If I sweep the VCO over it's frequency range I will
> hear the beating (two frequencies sounding together)
> changing and then disappearing at a few given points
> across the range of the VCO.  I believe these points
> are one octave apart.
>
> This goes away completely when power the VCO alone.
> However, when I add one or more additional modules
> from my PSU the beating returns and becomes worse with
> each additional module.
>
> Any ideas about what this could be?  Thank you in
> advance for any help!
>
> -Mark
>
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