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How to get rid of hum noise ?

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Member level 2
Sep 17, 2001
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Hello :)

I bouth the PC video card with composite TV out. Of course now I want to watch films on TV, so I connected video-output and sound-card output to TV trough SCART cable connection.

It all works well, video is great, but all the time there is disturbing hum noise at the back of the audio signal. My brother for example connected his computer to TV the same way I did and it works perfect for him.

At my friends house I tried to connect his PC with Hi-Fi stereo amplifier and he too have the same problem with hum noise, but at his place that noise is so disturbing you can't listen to anything.

I heard that could be the problem with ground potential mismatch, but I don't think that's the case in my problem. My cable (about 5m) is well shielded. At first I didn't connect audio ground and video ground to the shield of the cable, which is connected to the ground of TV and PC of course, so I thought there is some kind of ground problem. Then I connected all three grounds together and there were NO differences. I still get this anoying hum noise in the audio signal.

What should I do ??? Is it possible that could be sound-card giving me the grey hair ?

Thank you for all your help in advance.


ground noise

Hi Rostfrei,
the simplest solution is to break the existing gnd loop (some of your connected devices have more gnd return paths,and could be due also by the antenna amplifier power supply, that is normally fed thru the antenna cable), by inserting a 1:1 600ohm audio xformer in the audio path. (two required for stereo program).
Such xformer are easily available from component supplier.
(not choose of course the superpro models)
Hope help


Hello zurben

What do you mean by breaking the ground loop? What does antenna amplifier got to do with SCART input on the TV set ?

Should I "break" the audio line the similar way they "break" the video line on this page:

Waiting for your reply.


Your TV will not carry a ground at all. Everything is isolated. It is possible that when yoiu are connecting your sound card to your tv you are vertualy grounding the none live side of the chassis with an earth loop.(signal side) . This can cause mains hum and can realy be a problem to cure.

Plug the TV in next to the computer and use a very short audio lead with ONE SIGNAL SOUND EARTH up to the scart plug or no earth connection at all, is the noise reduced The video Line carries the ground for all signals is it OK. If not you will have to isolate the computer TV by as said 2 isolating 1 to 1 transformmers or use a GROUND LIFT BOX.

Hello barrybear

What is GROUND LIFT BOX ? :eek:


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