Laptopp mains hum on Hi Fi

Anybody had issues with connecting laptops to hifi and getting very audible mains hum?

A friend has it happeninig though I haven't been over to see it myself. It's fine on battery so I'm pretty sure it's just a cheap laptop PSU with the transformer causing all the grief.

I've told him to try moving it away from everything to minimize it's effect but does anybody else have any suggestions.

 

Could just be a ground loop. I wouldn't think it is a proximity effect. A few of the laptops I've tried have had ground problems and dump HDD and fan noise down the audio cable into the amp, I haven't really found a solution to it unfortunately. Computer psu's (though particularly laptops ime) cause all sorts of nastys when connected to other things. You can get isolation setups for them, pro audio suppliers should do them but they're expensive. Sometimes can be the difference between life and death though- recording DI from a guitar amp to a computer can be a very dangerous experience- I'm not sure where the potential builds up but as soon as you touch the guitar strings it finds it's ground. I've nearly had my wrist broken once from the shock of an incorrectly wired guitar. Nasty business.

 

I have had the very same problem with my laptop. I had all sorts of noise appearing from the speakers.
It is a ground loop problem and I used one of these -

http://www.maplin.co.uk/Module.aspx?ModuleNo=33172&criteria=ground loop&doy=28m8


Put it between the line out of the laptop and the input to the amp.
It seemed to work ok, though the the frequency response of the device only extends down to 40 hz so you do lose some quality. If you are just using your laptop to play MP3s then it's not too much of a problem.

I also tried lifting the ground on the laptop 240V power supply and this worked but I don't think this is a good idea, for safety reasons, better to use one of the above devices.

 

Definately not a good idea!

 

Choochter,

That's awesome. Thanks mate.

 

Lift the grounds, its cheaper than the maplin thing which also damages the quality.

Just one quick question, what areas of exposed metal are there on your laptop? It seems surprising to me that your laptop carries a ground.

 

Actually now you mention that, do they even have grounds at the laptop? Mostly they just seem to be 2 pin power and it is only the psu that is grounded. Which could explain the strange behaviour I've seen.
Will lifting the ground actually cure noise in the signal path though? Seems what is needed there IS a ground rather than lifting one further down the line.