Ground loop breaking resistor

[chingyg]

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

[pacificblue]

Yes to both.

[chingyg]

Thanks a lot

[tomchr]

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

[akis]

Yes, wire getting hot is worrying.

[wwenze]

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.

[Shaun]

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.

[pacificblue]

Originally Posted by wwenze

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.

Originally Posted by chingyg

Both of the grounds of the computer and the speaker are earthed

Originally Posted by wwenze

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.

[chingyg]

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.

[Shaun]

Originally Posted by chingyg

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.