Arny Krueger wrote:
Nick Gorham wrote:

Dave Plowman wrote:

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. ;-)

I have seen normal mains torroids used as valve output transformers.
Thay do a adiquate job, so they must let through (in that situation
anyway) 50hz.


The transformer is the secondary or tertiary line of defense. The power
supply itself carries the major burden.

Agreed, I was just pointing out that transformers on their own did
little, and as you say a cap input PSU with cheap rectifiers may well
create move crud than gets in from he mains.

Not sure however just how many power output stages are driven from a
regulated supply, I would have expected the pre stages to be fed from a
regulated supply.

--
Nick