[sdiy] decoupling modules from power lines?

[Dave Magnuson]

At 09:18 AM 1/10/02 +0100, Christian.Bergmiller at daimlerchrysler.com wrote:
>Hi,
>
>here is just another one joining the list...and the first message i'm
sending 
>is a question (what a shame) !
>
>I'm currently building a (small) modular synth with ASM-1 VCO's (added 
>tri/sine), polyfusion VCF (OTA design), 
>selfmade midi to vc (at89c2051) etc...
>Yesterday i discovered the VCO's had the tendency to lock (they even
modulated 
>each other - without any connection
>between them but the same power source) i fixed that by adding a tantal 
>capacitor from the V- to ground on both VCO modules
>(from V+ to ground seems to have no effect so i left them out so far)
>
>Now i'm thinking about equipping every module with a coil followed by a 
>capacitor to gound for the V+ and V- power lines.
>(tro prevent further problems so far undiscovered)
>I would try 1mH and 2,2uF, but would like to hear your suggestions bevor i 
>order a greator amount of these values from
>my favorite supplier...
>
>Hope to hear something helpful :-)
>
>Christian
>
>(and please don't mind the bad english...)
>

I use a small (100 Ohm) resistor in series, followed by .1uf and .001uF
film caps to ground on both supply lines. Even though you seemed to have
fixed the problem simply by changing the negative rail, I'd still put a cap
on the positive rail.  Who knows what your next new module will do to your
currently stable design... prepare for the worst and you're less likely to
have future problems.

If I recall correctly, you can use ferrite beads instead of the small
resistor, but I don't know what the benefits are, and the resistors have
worked fine for me so far.

Dave Magnuson

Resonant Frequency:
resfreq at hoohahrecords.com
http://www.hoohahrecords.com/resfreq/index.html