Limiting mains hum

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pop_disaster86

Guest
Hi

I'm a bit of a novice at this sort of stuff, so I was wondering if anyone could help me with a problem I'm having with my speakers. They are pretty basic ones that I picked up from the electronic store Maplins, but they do give surprisingly good quality. (There are 2 speakers, which are 30W power, with a 4" woofer and 3" tweeter each, and EQ built in).

Anyway, they have a Line Out jack, which I plug into the headphones socket on my laptop. However, if the laptop is also plugged into the mains (which it is most of the time), the speakers give off a really annoying humming sound, persumably being picked up from the mains supply, because when the laptop is not plugged in, they are totally silent.

Is there any way to stop this?

Thanks for any help
 
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RAY GANDERTON

Guest
Sounds like an 'earth loop'. Line level signals will not be clean from a speaker and I'm suprised these speakers have such a facility. Your pc should be connected to the 'line out' socket of your amplifier. The signal level here is normally around 1V p-p at 50k ohms. Otherwise make sure both your pc and hi-fi share the same earth connector. If your pc is battery powered then hum should not be an issue if disconnected from the mains.
 
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pop_disaster86

Guest
Yes that's correct, when the laptop is running on battery then there is no hum at all, but unfortunately I have it plugged into the mains a lot to charge, or just to save it running off battery power.

The trouble is that neither the speakers nor the laptop have an Earth connection in their plugs. I suppose there's not much I can do short of buying some better quality speakers with a better power supply?

Thanks for your help
 
K

kayojd

Guest
Go to radio shack and buy a ground loop isolator for 16.99.
Solves the problem.
 
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