In article , Andy Evans
wrote:
If you're *really* getting any difference ( try measuring ? ) then I'd
suggest you need to take a look at your incoming mains. It must be awful
in some unknown respect ( gross interference from industrial plant ? )

No industrial plants I know of. The differences with a mains isolation
transformer are subtle, but audible and very satisfying in fact. There's
always a danger of trying to seperate binaries such as "theory versus
practice" on this ng, and I'm simply reporting what I hear in this
instance. It may be the case that 'if you can hear a difference there's
something grossly wrong' but I somehow don't think there's anything
grossly wrong anywhere in this case.

Since you say the effect is "subtle" it may be reasonable to say that
nothing is "grossly" wrong.

However the simple fact that the extra 'isolation transformer' makes an
audible difference implies that either:

1) The amp is picking up some effect due to its own PSU not ensuring its
performance ignores any mains imperfections that are present in your case.
The 'isolating transformer' is acting to reduce this - perhaps as an
unintended side-effect of that individual unit's properties.

or

2) The 'isolation transformer' is *degrading* the mains in some way, and
altering the behaviour of the amp/PSU.

Either, way, I'd say something *is* 'wrong', but until you make some
relevant measurements and/or can be more specific it is difficult to say
much more.

Given some suitable measurements and analysis you might find a simpler
method for improving the performance - perhaps what you get now either with
or without the 'isolation transformer'. Can't say, though. Can only comment
that when I've encountered such effects I tended to track down what caused
them and was more satified with the results once this was done.

Slainte,

Jim

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