On Wed, 05 Jan 2005 23:46:28 +0000 (GMT), "Dave Plowman (News)"
wrote:

In article ,
wrote:

Much more likely to be poor decoupling in the PS / computer and
appearing directly on the audio output.

However, surely the PS would be a switch mode type, so producing no
audible hum?

Most recent ones probably are. But, judging by the weight and heat
they produce, older power supplies may well be linear.

It's an interesting problem...

The only explanation I can think of is that the return connection in
the PC to Amp lead is not continuous, than you wouldn't need much
coupling through the PS to generate lots of noise, but it may well be
O.K.with the PC operating on batteries.

Bill