[linux-audio-user] Re: The famous "Jack Hum" (Can't record and desparate)

Carlo Capocasa capocasa at gmx.net
Wed Nov 15 22:44:08 EST 2006


> I'd be surprised if this would turn out to be singing capacitor.
> Every switched-mode voltage regulator needs a an inductor, and
> these are much more likely to 'sing'. Probably you have a badly 
> designed or specified regulator that fails when the load is
> below a minimum value (a classic problem with SM regulators).
> To test this, load the power supply e.g. via the USB connectors
> (a simple USB powered keyboard light could be enough). 
> If you can locate the component, and it turns out to be an
> inductor, applying a bit of epoxy glue on the winding will
> probably silence it.

This is an EXCELLENT lead. Thanks Fons.

Can you give me a hint on how to identify an inductor? My notebook case
is open right now and the whine comes from a place out of or near the
CPU. Also, the whine comes when I start Jack at low latencies; I don't
quite understand what the purpose of loading the power supply would be;
I've hooked up my Palm Zire or a USB microphone (which sounded like
crap, but did load the power supply) and experienced no additional hum
whatsoever.

Carlo



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