Don Pearce wrote:
Eiron wrote:
Don Pearce wrote:
Eiron wrote:
Dave Plowman (News) wrote:
In article
,
philcud wrote:
Just started to get an earth loop using my laptop as source connected
to amp.
just starte
get 'cricket' type sounds when the laptop is connected to power lead.
problem goes totally when i half remove the power lead,
gets unlistenable when the power lead is removed and laptop
running on
battery.

only just started happening, any ideas?

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?


Never a problem. You don't get hum problems with battery-powered gear.

And what's the amplifier powered by?


Doesn't matter. You only connect to earth for safety.

That's not quite true. You sometimes connect to earth to eliminate hum.
I had a setup that wasn't earthed and when someone approached the microphone
it hummed; when they touched a chassis point it stopped humming.
That wasn't an earth loop but it was capacitative pickup of mains
interference as the ground of all the double-insulated kit was
floating at a hundred volts or so. Earthing the amp cured it.
Modern laptop PSUs have three core mains leads so it probably
doesn't happen on new kit.

--
Eiron.