your powersupply is probably leaking... if you dont want to get a new one try moving it as far away as your other wires as possible. powersupplies start doing this when they get old and banged up

the power supply on my laptop? it is brand new. we also tried his laptop with his power supply and it did the same thing.

if you are talking about the power strip, i tried plugging the laptop directly into the wall but it still did it. any other ideas?

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try getting a power conditioner...can't guarantee it'll solve your problem tho.

one such example:
Furman Rackrider RR15 Rackmount Power Module with Lights

All RR Series conditioners protect your delicate electronic equipment by combining high voltage varistor (MOV) surge and transient suppressors. The fast-acting suppression circuit quickly responds to clamp transient voltages to safe levels.An RFI/EMI interference filter works to prevent noise from fluorescent lights, certain dimmers, radio transmitters, and similar sources of "electronic pollution" from contaminating the AC line and from there, leaking into sensitive audio, video, or computer circuits. The RR-15 is NRTL/TUV listed.

65 bucks @ zzounds.com

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The interference you heard is a 60 Hz hum, right?

The problem is almost certainly to do with different 'earth' levels in your mixer and laptop. The mixer's earth is probably pretty good, as audio equipment is set up with earth paths in mind. The laptop's power supply is probably the culprit. Have a look at it -- does the power plug have an earth pin on it? If not then bingo here's the problem, if so then it might not be connected. This isn't that uncommon.

The way to test this theory is to get a multimeter, and check the AC voltage between the laptop's earth and the mixer's earth. If you get a voltage above 1 volt or so then this is your problem.

There are two ways to get around the problem.
1) Connect your laptop's earth to the mixer's earth. Grab some wire and somehow connect it to your laptop's earth. The best way to do this is probably to get a screw that fits into a nut on your serial port, put the wire underneath this screw and screw it down tight. Then connect the other end of the wire to the mixer's earth (the one on the back that's used for turntables etc). You will probably still hear the hum, but it will be a lot fainter.

2) Use an isolation transformer. This is a 110V - 110V transformer that isolates the line voltage from earth potential. Technicians use these to stop themselves getting electrocuted.

Let me know how it goes.

Cheers,
Ben

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I am artificially intelligent.

i am assuming by earth you mean the grounded wire? the third prong. if so my laptop is grounded.....i will try and ground it to the mixer though. thanks.

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