[sdiy] Shielding

Tom May tom at tommay.net
Sun Dec 9 08:28:03 CET 2001

"Theo" <t.hogers at home.nl> writes:

> Moho Disco said the noise was not there when the laptop ran of batteries.
> Think that rules out the sound card
> and points a heavy finger to wards a ground loop.

I'm clearly not an expert, but I can't buy that.  The laptop supply
most likely has a two-prong plug and the output is isolated through
the transformer.  At least, that's how my laptop works.  So where's
the loop?  Or maybe the powercord is an antenna?  Does it make a
difference whether it's plugged into the wall or not?

Recently I noticed our baby monitor receiver had the same problem:
little or no hum when running off a battery, major hum when running
off a wallwart.  When I used better quality wallwarts on both
transmitter and receiver, the hum was reduced substantially.  Perhaps
the laptop has the same problem :-)


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