[sdiy] Module Messing with my PSU (i think)

[Harry Bissell Jr]

Are you looking with an oscilloscope ???

Often, if the offending module is oscillating
untrasonically... that high frequency can carry
down the power supply rails and influence sensitive
points in other circuits.

One really sensitive point is the comparators in
VCO / LFO circuits. Just a little noise at this
point will change the frequency a lot.

Well designed modules will have these points sourced
from an ON-CARD voltage reference that would er...
decouple the trip points from the power supply.

I was working with an EFM VCF once... and when I would
turn the frequency of the filter all the way up...
The VCO (VCO4D) would drop in pitch.

The filter would oscillate at the really high end...
and the ramp reset comparator in the VCO was
referenced from a voltage divider on the +15V rails. 
There were
decoupling caps on the board... but they were in the
wrong place to decouple the actual point the noise is
hitting...

and all this with a decent, linear power supply.

Interested persons should seek out the quatation about
the "snowflake" from the story "The Subways of Tazoo"
by Colin Capp.

H^) harry



>   -----Original Message-----
>   From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf
> Of Benjamín Velasco
>   Sent: Thursday, March 30, 2006 7:25 PM
>   To: Synth DIY List
>   Subject: Re: [sdiy] Module Messing with my PSU (i
> think)
> 
> 
>   Hey i think i've found somethig!. After removing
> all the ics from the
> board I powered my synth, waited a few minutes and
> then connected this
> module. Without the ics theres no problem. Then i
> connected the ics of one
> of the LFOs whose rate can be controlled manually
> and i could hear somehow
> the rate in the varying pitch of my oscillators. The
> same happened with the
> other LFOs. I quite new at this stuff but im sure
> there is be a simple
> solution to this. Please help me!!
> 
>   Benjamín
> 
>