[sdiy] Microphonics

Ben Stuyts ben at stuyts.nl
Mon Jan 22 17:35:13 CET 2018


I’ve had bad experiences with certain ceramic caps in a measurement amplifier I once designed. Any movement / shaking of the board would find its way into the output channel. Turned out to be a multilayer ceramic cap which was particular high microphonic. It is a piezo effect so my guess is that it could go both ways. Any multilayer ceramic caps in there?

Here is an article describing it: https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2014/12/19/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-1 <https://e2e.ti.com/blogs_/archives/b/precisionhub/archive/2014/12/19/stress-induced-outbursts-microphonics-in-ceramic-capacitors-part-1>

Ben


> On 22 Jan 2018, at 17:15, Tim Ressel <timr at circuitabbey.com> wrote:
> 
> 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
> 
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