[sdiy] Microphonics

Miles Stevens milesstevens89 at gmail.com
Tue Jan 23 08:08:08 CET 2018


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> 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> 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>
> 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>timr at circuitabbey.com
>
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> --
> --Tim Ressel
> Circuit Abbey <timr at circuitabbey.com>timr at circuitabbey.com
>
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