Unwanted fm through power supply

[Dan Higdon]

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.  :-)

----------------------------------------
hdan at charybdis.com
"Trust not the monkey, nor his clever schemes" - hdan