[sdiy] keeping signals seperate..avoiding noise

George Hearn georgehearn at btinternet.com
Fri Nov 14 11:18:33 CET 2008

Maybe try some R-C decoupling of the offending chip, sometimes fast digital
edges will propagate freely to other circuit parts (specially x10 gain amp).
By inserting a small resistance in the power supply to the switching IC you
can sometimes slow these edges down a bit.  Might help, might not.  George

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dan Snazelle
Sent: 14 November 2008 04:29
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] keeping signals seperate..avoiding noise

a few questions

if i have a clean source going through a buffer and then that splits into
one half going into a PLL and a divider and the other half getting boosted
by a x10
opamp stage...WHY would i be hearing the divider sounds in the background of
the clean stage?

this is very different than my lfo bleedthrough of the other night (into the
vco) but it is similarly noisy.

i have all pcbs on metal standoffs going into a metal box....could this
cause the high frequencys of the PLL signal (and octave down) to bleed into
the clean opamp? (though none of the standoffs touch traces)

maybe i should put a regulator JUST on the divider board?

i have bypass caps.
pretty good ground planes.
and seperate lines for digital and clean grnd.

what about a bunch of wires laying all over each other or being
bundled...can this cause signals to mix?

i think i really need to understand noise better.

any good books on this?


check out various dan music at:



(or for techno) http://www.myspace.com/snazelle 

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