In article ,
Mike Gilmour wrote:
What constitutes 'dirty' mains anyway? What about utilities signalling
systems, mains borne baby alarms, intercom systems etc, not as
invasive as Stewarts suggestion of a neighbouring welding shop but
pollution never the less. I'm way out the in country but 'scoping my
mains showed evenly spaced spikes... tracked down to an electric fence a
third of a mile away. ;-)

A well designed mains transformer will attenuate anything outside about 50
Hz by a considerable amount - if it didn't, decent audio transformers
wouldn't be so expensive. ;-)

Here in London, the mains is anything but a pure sine wave - I'd guess
because of all the SWPS around.

--
*Don't worry; it only seems kinky the first time.*

Dave Plowman London SW 12
RIP Acorn