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Old 22nd December 2003, 05:36 PM   #1
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Default Ground loop problem- laptop computer to mixer

I'm having trouble with a ground loop with a laptop computer hooked into my DJ system. Its using the unbalanced 1/8" line out on the computer (a Dell) to the 1/4" unbalanced inputs on the mixer board. Now, I only have this problem when I have the computer's power supply plugged in. It is a 3 prong line lump style adaptor. I have not tried to lift the 3rd pin yet (im at work rite now, and I dunno if I can find my cheater plugs). If I run the computer off the batteries it is fine and dandy.

I have 2 DJ cd players as well that are unbalanced and those do not have any problem. Help!
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Old 22nd December 2003, 05:41 PM   #2
SY is offline SY  United States
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Well, the sure cure is to use a transformer between the laptop and the DJ system. Galvanic isolation is a powerful thing!
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Old 22nd December 2003, 05:54 PM   #3
azira is offline azira  United States
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Yeah, I have this problem too when I use my laptop to play music on my home stereo. Even if the laptop is plugged into the same socket it'll have the problem. The laptop is so compact and the PS is on the opposite side of the laptop from the soundcard. Dell still makes the best laptops though.
Anyway, like the prev post says. Get a DI box from a music store and use the ground-lift option. Check the freq-response on the box when you buy them since you'll need it for DJ music. They will convert your 1/4" to XLR however. ~$20 each for a decent active one.
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Old 22nd December 2003, 06:36 PM   #4
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I used to buy isolation transformers from these guys:

http://www.rcicustom.com/index2.htm

They were decent transformers for not a lot of money. I think the part number was something like 60L60. They donít list them on the web site, but if you call them they can likely help.

If your in MD near DC Chuck Levinís Music is a good place to buy DI boxes, and there is also Markertek,

www.markertek.com
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Old 22nd December 2003, 06:44 PM   #5
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Gain stage issues can exacerbate ground loops. I needed to insert a pad between my laptop and desktop speakers to keep from hearing the PCís bus noise when the curser moves. In my case itís a 10k stereo pot from Radio Shack stuffed into an aluminum box.
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Old 22nd December 2003, 07:09 PM   #6
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Is there anything else that's earthed connected to the same mixer? If so, can you break that earth connection without compromising electric safety?

For example, if you have a tuner with an earthed antenna cable, you can insert two small 100nF capacitors between the antenna cable and the tuner, one for the ground and one for the centre conductor.
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Old 11th February 2011, 02:23 AM   #7
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Default RF ground loops

This is the most baffling thing, and occurs quite often with camcorders when you take any audio signal from a mixer. Even when there is obviously NO ground connection from the camcorder or even the mixer, to the AC mains. Think about this-- it's NOT a classic "ground loop", yet, we are hearing the buzz when we use the power brick on the camcorder (or laptop). I will have to conclude that what we're hearing is an RF ground loop to the other device-- RF signals from the various devices, down the cord, thru the power brick and thru the house mains. Or, a simple RF path to ground, causing my camcorder (or your preamp) to recognize RF which is equally present when running on batteries, but has no ground path.

Some of this may be reduced by ferrite beads on everything-- all cables in/out of your devices. If there's no RF in your device, or the other device, the existence of a ground path does not matter.
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Old 17th February 2011, 03:51 PM   #8
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Those laptop power adapters are switching power supplies. A chip watches the input 110/220 and is constantly switching on and off to keep the DC output constant. They generate a lot of RF noise. One solution would be to buy a supplemental battery that fits in the extra bay of the laptop and gives you a lot more run time. You may also need a new main battery as these start to deteriorate after about 300 to 400 charge/discharge cycles.

Al
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Old 17th February 2011, 04:40 PM   #9
poynton is offline poynton  United Kingdom
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My son had exactly this problem on his DJ setup.
He runs 2 laptops as well as the CD decks and mixer.

It was cured by using a couple of these :-

GROUND LOOP ISOLATOR WITH GOLD PLATED CONNECTORS on eBay (end time 13-Mar-11 10:24:04 GMT)


Andy

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Old 18th February 2011, 03:04 AM   #10
cbdb is offline cbdb  Canada
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Quote:
I have not tried to lift the 3rd pin yet (im at work rite now, and I dunno if I can find my cheater plugs). If I run the computer off the batteries it is fine and dandy.
Never lift (disconnect) the ground pin!!! The person you electrocute could be yourself.

If the ground pin is the problem, replace the laptop power supply with one that doesnt need a ground pin.
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