[sdiy] SBM VCO CV interference

[vitreousflux]

Hhaah I thought of that, but no....I think...

The +12V and -12V are 'pure' signals according to my scope.....

Here's something... When I tweak the pulsewidth pot, the half-wave part of
the unwanted harmonic changes phase.... weird. I see the same interference
tapped off of the 393 pin 3 directly, too.

Perhaps it's some kind of feedback thru ground? The PW pot is on the
complete other side of the circuit!

Could it still be an emi problem yet?

Rob



----- Original Message -----
From: "tomg at efm" <efm3 at mediaone.net>
To: "vitreousflux" <vitreousflux at wwnet.net>; "`Synth DIY Maillist"
<synth-diy at node12b53.a2000.nl>
Sent: Monday, April 16, 2001 9:22 PM
Subject: Re: [sdiy] SBM VCO CV interference


>
> It's truly wierd...I've just been going over the sbm on my bench
> and see nothing like what you are describing. Is your TV on?
>
> Tom
>
>
>
> > On my EFM SBM, I am getting a strange problem.
> >
> > On my input CV line which consists of 1 input and 3 tune pots (freq,
fine
> > and init freq trimmer), I am getting an odd narrow pulse-wave signal on
my
> > scope - it changes frequency along with the signal CV.
> >
> > This causes weird harmonics in the output signals (sine, tri, saw, pul)
> and
> > is most noticeable at higher frequencies.
> >
> > The pulse wave seems to actually be two signals: a full cycle narrow
> pulse,
> > and a half-cycle (positive only) at 90 degrees offset. How bizarre!
> >
> > I checked all my grounds and traced the problem back from the opamps,
but
> > have no where else to check the signal - it's the start of the
circuit! -
> I
> > am using no input on the cv (although have tried using a cv input which
> does
> > not help the problem).
> >
> >
> > Anyone else run into a similar problem on their SBM or analog synths?
> >
> >
> >
> > Rob
> >
>
>