[sdiy] Microphonics

Tim Ressel timr at circuitabbey.com
Tue Jan 23 16:25:10 CET 2018


Interesting idea. And they're only four adult male dear at harbor Freight.

--tr


On 1/22/2018 11:08 PM, Miles Stevens wrote:
> Do you have an automotive stethoscope? I would grab one of those and 
> probe around
>
> On 23 January 2018 at 09:02, Roman <modular at go2.pl 
> <mailto:modular at go2.pl>> wrote:
>
>     So that narrows it down to capacitors close to VCO core, like
>     timing cap, decoupling caps around reset circuit, or caps around
>     sub-osc divider if you have one there.
>     A photo of the board might bring some ideas also.
>
>     Roman
>
>     Dnia 22 stycznia 2018 22:44 Tim Ressel <timr at circuitabbey.com
>     <mailto:timr at circuitabbey.com>> napisał(a):
>
>         Yes, it tracks vco frequency. No switchers. Power draw is low
>         so I don't think its the big electros.
>
>         btw microphonics can go both ways. It is caused by the
>         dielectric being piezoelectric, and that can both generate and
>         absorb sound.
>
>         --tr
>
>
>         On 1/22/2018 11:31 AM, Roman wrote:
>>         Is whining somehow related to VCO frequency?
>>         Do you have any DC/DC converter?
>>         My first guess would be the largest ceramic cap you have there.
>>         Or electrolytic capacitor run over maximum ripple specs.
>>
>>         Roman
>>
>>
>>         Dnia 22 stycznia 2018 17:24 Tim Ressel <timr at circuitabbey.com
>>         <mailto:timr at circuitabbey.com>> napisał(a):
>>
>>             Got a weird one...
>>
>>             An oscillator I designed is whining. Well, some units do
>>             it. It is faint
>>             and you have to have your ear right up against the board
>>             to hear it. But
>>             an end user complained so we had to investigate. Other
>>             weirdness ensued
>>             but we got the customer taken care of.
>>
>>             My question is: how to find where the whine is coming
>>             from? I tried
>>             using a microphone but could not pick anything up. This
>>             is an ASM-1 type
>>             VCO (saw core) so there is a pulse train present. That
>>             could explain the
>>             mic not picking it up. I tried putting my finger over
>>             various components
>>             on the board with no luck. I thought about using an
>>             accelerometer but it
>>             would have to be high sensitivity and low mass to work.
>>
>>             I am at a loss.  Any thoughts?
>>
>>             --
>>             --Tim Ressel
>>             Circuit Abbey
>>             timr at circuitabbey.com <mailto:timr at circuitabbey.com>
>>
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>
>         -- 
>         --Tim Ressel
>         Circuit Abbey
>         timr at circuitabbey.com <mailto:timr at circuitabbey.com>
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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