Unwanted fm through power supply

[Christian Hofmann]

On Tue, 1 Sep 1998 14:41:39 -0500
"Dan Higdon" <hdan at charybdis.com> wrote:

> From: Hcabnivek at aol.com <Hcabnivek at aol.com>
> >Help! I've just finished my new quad lfo module and in doing an initial
> hookup
> >to my rack power supply for testing I find that there is a BAD fm in my two
> >CEM3340 based VCOs.  This occures when power from the common supply is
> applied
> >to the lfos, no patch has been made.  The fm is directly related to the
> >frequency of the lfos.  The lfo is a design by Klein/Hutchins (from
> <snip>
> 
> I had this problem, and ultimately the solution was to get a beefier
> power supply.  I was using a PAiA supply (which, in fairness to
> PAiA, I think I had lightly cooked) which just didn't produce enough
> juice.  However, your supply looks to be pretty hefty, so I don't know.
> 
> The comparators in that LFO really spike the supply.  You might want to
> try adding some .1ufd caps to the LFO in addition to the larger caps.
> Also, it might work to put some very small resistors (100 ohm) in line
> with the power supplies to limit current consumption (150 ma ought
> to be plenty), but I've never tried anything like that, and it might be a
> colossally stupid idea.  :-)

Hi,
that reminds me of that nasty audio noise coming from the LFOs I had
ages ago in the Elektor Formant. Never quite got rid of it, I ended up
using an additional El Cheapo PSU just for the LFOs. Not extraordinarily
nice, but it worked :-)

cu
Christian