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Old 20th December 2009, 02:03 PM   #1
chingyg is offline chingyg  South Africa
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Default Ground loop breaking resistor

I have a DIY self powder speaker that I wished to use with my computer. Both of the grounds of the computer and the speaker are earthed, which introduces a ground loop. Sometimes the current in the loop can cause the shield of the interconnect cable to go really hot. and it introduces humming.

To solve the problem I added a 10R resistor in series with the interconnecting cable's ground line. It appears to solve the problem.

Is this an acceptable way to help with ground loop? is it safe to do this?

thanks
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Old 20th December 2009, 05:58 PM   #2
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Yes to both.
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Old 20th December 2009, 06:18 PM   #3
chingyg is offline chingyg  South Africa
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Thanks a lot
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Old 20th December 2009, 09:42 PM   #4
tomchr is offline tomchr  United States
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I'm surprised the current in the ground loop is enough to heat up the cable. Are the two connected to the same ground? And is this ground actually grounded?

~Tom
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Old 21st December 2009, 09:02 AM   #5
akis is offline akis  United Kingdom
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Yes, wire getting hot is worrying.
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Old 21st December 2009, 10:19 AM   #6
wwenze is offline wwenze  Singapore
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How many amperes is required to heat up a wire

The grounds of the computer and the amp are at very different levels, I suspect bad design.
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Old 21st December 2009, 11:03 AM   #7
Shaun is offline Shaun  South Africa
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chingyg

I would not continue using the equipment this way, even with a 10R resistor.

BTW, where in SA are you? Perhaps some locals can help you out.
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Old 21st December 2009, 12:25 PM   #8
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Quote:
Originally Posted by wwenze View Post
How many amperes is required to heat up a wire
Depends on the wire diameter and the ambient temperature. But it only takes few volts to achieve many amperes, because wires usually have low impedance.


Quote:
Originally Posted by chingyg View Post
Both of the grounds of the computer and the speaker are earthed
Quote:
Originally Posted by wwenze View Post
The grounds of the computer and the amp are at very different levels, I suspect bad design.
If both grounds are earthed, there should be no different levels. Something is probably wrong with the outlets they are connected to. Different earth potentials usually turn up, when N and PE share the same wire until the outlet. If that is the case, you should have the electrical installation in your home revised by an electrician urgently.

What you can do to avoid different potentials is to connect both the computer and the amp to the same outlet with a multiple outlet strip.
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Old 21st December 2009, 03:11 PM   #9
chingyg is offline chingyg  South Africa
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Thanks for the reply guys. Well here's some updates

The amp and the computer is connected to different outlet, and I think all the outlets goes back into the switch box of the house, so that's a long loop.

The wire was not only hot, the current actually melted the tracks on my computer's front audio socket panel, but I don't think it is the loop current, I suspect that during that test, the ground for the prototype amp broke off from the supply (twist wire method) so all of the return current had to go through the interconnect cable and computer.

When I rewired the amp, the cable isn't getting heated up anymore, there was just a irritating hum noise. Now with the added 10R resistor, the hum disappeared.

and Shaun I live in George, Western Cape, so far i don't know of any local audio enthusiasts. It would help if u knew some.
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Old 21st December 2009, 03:48 PM   #10
Shaun is offline Shaun  South Africa
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Quote:
Originally Posted by chingyg View Post
I suspect that during that test, the ground for the prototype amp broke off from the supply (twist wire method) so all of the return current had to go through the interconnect cable and computer.
I think you're probably right about this; I have had a similar thing happen to me.

I don't know any DIYers in George, but you never know. If you're looking to hook up with like-minded individuals in your area it might be worth giving a shout on AVforums.co.za.
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Last edited by Shaun; 21st December 2009 at 03:49 PM. Reason: spelling
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