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Old 19th January 2013, 05:38 AM   #1
Zertman is offline Zertman  United States
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Default How do get rid of massive computer noise?

Hi everyone. I am trying to use my car's amplifier on my computer and getting a lot of computer noises, for instance, when I move the mouse or load up programs the noises gets really loud. When I take the analog rca input jacks from the amp, the noise is totally gone. Since there is no volume on the amp, I am using 47k resistors on the analog line-level inputs of the amp. The amp is using the computer's power supply but I don't think that is the problem because I tried using a separate power supply and it still had the same noises. I have also tried moving and protecting all the wires but it didn't help. Any help on getting rid of these noises would be very much appreciated. Thanks.
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Old 19th January 2013, 07:08 AM   #2
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Its called 'common-mode noise' and is the bane of any digital system. You could try installing an amp card inside your computer - I used to have a Tripath one in mine which worked a treat. Screening wires doesn't help (the noise is conducted not radiated) but wrapping ferrite clamps around cables might.


<edit> To get any handle on how to fix it you'd need to post up schematics for how the amp's connected to the computer and any PSU, with indications of how everything's grounded/earthed.
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Last edited by abraxalito; 19th January 2013 at 07:10 AM.
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Old 19th January 2013, 09:14 PM   #3
Zertman is offline Zertman  United States
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I did some more testing. The noise does not get louder or softer with the computer's main volume or any other volume. Also if I just have headphones plugged into to the computer, the noise is not there. Its a four channel amp so I tried plugging in the headphone for the front and keeping the amp for the rear and the noise was not in the headphones but was still in all 4 channels of the amp's output.
Here is the schematic of my system:
Click the image to open in full size.

Last edited by Zertman; 19th January 2013 at 09:39 PM. Reason: Correcting picture
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Old 19th January 2013, 11:33 PM   #4
Zertman is offline Zertman  United States
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Never mind, I removed the resistors and the noises are now gone. I think it was a loose connection on the ground on the ground input of the amp. Thanks for the reply, though.
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Old 20th January 2013, 08:28 AM   #5
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Thanks for the schematic - I agree no need for the 47ks. You might be getting a CM noise problem because of the subwoofer's contribution to a loop - for the best sound make sure the sub is powered from an adjacent socket to the computer's power, keep the loop area of their cables as small as possible.
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Old 23rd January 2013, 09:48 AM   #6
RNMarsh is offline RNMarsh  United States
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When ever you put a series R in any cable line, it raises the Z of the entire cable... making it suscptible to RFI/EMI. -RNM
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Old 31st January 2013, 01:27 AM   #7
T Leung is offline T Leung  Hong Kong
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Quote:
Originally Posted by RNMarsh View Post
When ever you put a series R in any cable line, it raises the Z of the entire cable... making it suscptible to RFI/EMI. -RNM
What is the purpose of the series R? To attenuate the signal level?
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Old 31st January 2013, 02:01 AM   #8
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They (the 47ks) serve no purpose at all in this application.
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