On Jul 10, 10:31*am, "Dave Plowman (News)"
wrote:
In article ,
* *Eiron wrote:

Earth loops occur when there are two ground paths at different
potentials. Usually the screen of the interconnecting cable and mains
earths via the mains plug. And takes the form of hum. If you are
running the laptop on batteries with the power supply disconnected
totally it can't be an earth loop.
Could the problem be that there is no earth in the system
rather than too many?

If there's no ground connection between the two using unbalanced
connection you'll not get any signal either.

--
*If a parsley farmer is sued, can they garnish his wages?

* * Dave Plowman * * * * * * * * London SW
* * * * * * * * * To e-mail, change noise into sound.

Many thanks for the replies.

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