philcud wrote:

The distortion is at its worst when the power supply is disconnected
from the laptop, with the laptop running purely on battery power - the
distortion sounds like an earth problem, but very, very loud, totally
overpowering any signal.

with the power supply attached it has a high pitched 'cricket' type
distortion that changes depending on what the computer is doing (ie if
i load the processor it changes).

lastly, if i 'half' remove the power lead from the laptop, such that
the laptop tells me that it is not receiving any power from the lead,
but the lead is still halfway in the socket (maybe earthing?) there is
no distortion to the signal whatsover.

the laptop is an old audiolab powered by a 'kettle' type lead (3
prong).

hopefully this helps


What an extraordinary row about earthing! I haven't bothered to read all
that branch, but I don't think that there's anything useful top be
learned apart from the fact that someone here has anger management
issues and is best avoided.

Well, how did you get on? any more evidence/ symptoms?
Have you got anything else attached to the laptop beside the amp?
(earth problem)
It does seem likely that something is pulling your 0 v around.
If you remove that something and the hum goes away then when you listen
to music (not classical) with vocals do they sound weaker than they
should? If Eeyore's diagnosis of the jack plug is correct then each
channel will play the difference between left and right and that's what
it will sound like.

you might also find that the 'something else' is connected to the mains
by a two pin plug and that reversing it solves the problem (I know that
this shouldn't happen, but I have seen it).

Let us know how it goes anyway.
Roger Thorpe