[lug] audio interference question

[Davide Del Vento]

>> i plugged the stereo out of my laptop into a really nice power amp / speaker combo i normally use for recording.
>>
>> when the laptop is NOT plugged in (running purely on battery), the sound is pristine... exactly what i'm looking for.
(snip)
>> here's the catch.. the minute i PLUG the laptop in to POWER IT (non battery), i get a an annoying but constant static / hum / interference sound.

> It sounds to me like you may have a ground loop problem. A ground loop
> occurs when there are multiple grounds and the current through the
> ground causes a voltage to develop between the different ground
> points. The fact that the problem disappears when you run your laptop
> on its battery is a big clue.

The other thing you didn't say, is if you have the same constant
static / hum / interference sound when the laptop is plugged into the
power, but you are using a different device to amplify the sound (or
headphones, but a better test will use the same line out, thus you
should try battery powered speakers).

If the problem goes away with the laptop plugged into the power, and
the speakers being on battery, then it's a ground loop.

I suspect that the problem will still be there. If so, it's not a
ground loop. In such a case the problem is (somewhere) in the power
supply of the laptop, not being enough "clean" for audio purposes. If
that would be the case, you might have some luck changing the power
brick, but don't take it for granted.

Bye,
;Davide