[sdiy] two VCOs on 1 PCB - problems

[David G Dixon]

I fancied building two TH VCO-1s on a single board for myself several years
ago, and was firmly discouraged from doing so by several people I considered
more knowledgeable, for the very reason you are experiencing: soft-syncing
between the two VCOs.

Have you shared any opamp or comparator chips between the two VCOs?  That in
and of itself would cause soft syncing.  The two circuits need to be utterly
separate, at the very least.

If not, then have you tried installing additional decoupling caps on the
power rails very near to the comparators?


> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of neil harper
> Sent: Thursday, December 27, 2012 1:04 PM
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] two VCOs on 1 PCB - problems
> 
> hi everyone,
> seasons greetings from canada
> 
> as my christmas project, i built two Thomas Henry VCO-1's on 
> a single protoboard. so far everything seems like it's 
> working and sounds great, but I am noticing a few "quirks".
> 
> - as the tuning of each oscillator gets very close, they seem 
> to lock together.
> 
> - when the oscillators are tuned close, i believe i'm hearing 
> one of the oscillators reset (sounds like an occasional 
> 'tick' maybe once every second - goes away when i detune the 
> other oscillator).
> 
> i only have experience doing circuit boards for small digital 
> stuff, so i know this is a bit over my head as a first synth 
> project. :) i'd like to make this on a proper PCB for myself, 
> so does anybody have any tricks i can do on the PCB layout to 
> eliminate these problems? 
> 
> 
> 
> --
> //neil harper
> 
> 
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