In article , Glenn Richards wrote:
The main reason I was asking... as I said in an earlier post, because I
work from home I've got about a dozen PCs sitting in the next room, on
the same ring main as the hi-fi. Which makes one wonder just how much
crap is getting onto the mains.

Mains is full of crap anyway. Have you ever looked at it with a scope?
Sometimes it looks nothing whatsoever like those neat sinewaves in the
textbooks, but the power supplies in any electronic equipment running from
it will transform it, rectify it, filter it and stabilise it and thereby
turn it into clean DC for the electronics itself because that's what power
supplies do. Filtering the mains will have no additional benefit.

Rod.