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Roscoe
07-11-2008, 11:42 AM
I am running music from my laptop into a sound desk, then to be amplified.

Plugged into the power (battery charging) there is a loud humming, almost feedback, sound.

Not plugged into the power, no noise at all.

Unfortunately, as is the case with all laptop batteries, it runs out of power quite quickly, so it needs power once more and the noise returns.

Obviously has something to do with the power cord and lead to the sound desk. Perhaps it makes some sort of loop?

Any ideas how I am able to rid myself of that annoying noise?

Thanks,people.:thanks

Driftwood
07-11-2008, 08:53 PM
Don't know if this will help but when I connect my PSP via USB into my desktop PC I get a very similar sound from the PC speakers.
I havent looked for a solution as it's not a problem but I would suggest you open your sound manager & experiment with ticks in boxes. Just try one at a time & remember what you've done or you may finish up worse off.

feersumendjinn
07-11-2008, 09:39 PM
I'd say you've either lost some power regulation in your charger allowing 50hz AC mains hum to get through (try a different charger, or get that one tested with an oscilloscope (and repaired?)); or you've developed a "ground loop hum" from the charger circuit to the laptop to the sound desk and then the amp, perhaps this Google search will help with that (also try plugging one or two of those units into a different wall socket circuit (in another room?)).
http://www.google.co.nz/search?q=how+to+fix+a+ground+loop+hum&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

apsattv
07-11-2008, 10:00 PM
Go in your sounds settings and adjust "PC Speaker" to the lowest possible volume. Then also tick at the bottom to mute it.

jwil1
07-11-2008, 10:08 PM
Is it a high-pitched 'screeching' sound?

If it is, I had the same problem - only solution I found was to unplug the power lead when connected to the desk, which isn't an option for you :(

Occasionally I could put the system into hibernation, them start it up again and it wouldn't screech.

Roscoe
10-11-2008, 08:16 PM
Thanks for your suggestions, people.

Feersumendjinn: After looking at some of those Google searches, I went along with the ground loop theory. Although their solutions were not practical in my case, I put an isolating transformer before the laptop power which, while it has not entirely eliminated the problem, has dropped the noise to a more acceptable level.

Jwil1: You're correct. And yes, unplugging the power does work, but as you say; not an option. The batteries are not known for their lasting power!