[sdiy] Microphonics

Tim Ressel timr at circuitabbey.com
Wed Jan 24 14:07:49 CET 2018

Well, if you must pry..  ;-)

Being a Eurorack widget it had a separate board for the jacks and pots 
and switches. I know that the whine is downstream from the VCO core 
because if the control board is removed, the VCO section is disconnected 
from the downstream processing and the while goes away. Now here is the 
weirdness: some control boards cause the whine, some do not. Or at least 
that is what the client tells me. He sez he replaced the control board 
and fixed the problem.

--tim (scratching head) ressel

On 1/24/2018 4:54 AM, rburnett at richieburnett.co.uk wrote:
>>> The author meant “bucks” which is what dollars are often called.
> I was more concerned about this comment!!!...
>>> ...other weirdness ensued but we got the customer taken care of.  :-O
> If the integrator capacitor in the VCO is piezoelectric then it will 
> generate a force that is exerted on the PCB when it charges and 
> discharges.  This alternating force will then excite various 
> mechanical resonances in the surrounding PCB.  (The PCB will move more 
> air than the tiny capacitor alone so it will probably just sound like 
> the PCB is making the whining noise.)  Also, a mechanically flexing 
> PCB will exert a force on the capacitor resulting in electricity being 
> generated in the capacitor due to the piezoelectric effect.  So this 
> has the potential to mess up the electrical operation of your 
> precision VCO.  I would expect that the operation of the circuit will 
> begin to be influenced to some extent by the mechanical resonant modes 
> of the PCB!
> -Richie,
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--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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