[sdiy] two VCOs on 1 PCB - problems

Dave Leith dave.leith at gmail.com
Thu Dec 27 23:19:36 CET 2012

I built a version using my own layout of the Buchla 259 dual VCO  on a
single board (as the original was) and originally had some syncing
problems. Tried a number of solutions from separating power supply to
each VCO, extra decoupling but pretty well solved the problem by
rerouting off board wiring that was near the fc inputs. Anyway that's
what worked in my case.


On Thu, Dec 27, 2012 at 2:00 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> 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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