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Thread: noise investigation

  1. #1
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    noise investigation

    After wiring everything into my vehicle, there is noise which I anticipated. Right now I need to investigate where my noise is coming from. Here is what I have right now:

    2 OPUS with 8 gauge wire right from the Battery
    a ignition control wire turn on the power inverter and trigger the OPUS
    a common ground in the trunk where i grounded EVERYTHING together

    Right now I am using TV out from my carputer. The RCA goes into a AV switcher, which then go to my headunit and other LCD screens. Other components connected to the AV box includes a PS2, and a VCR.

    If I connect my computer through the AV box, I get alternator whine. If I bypass the AV box and go straight from computer to headunit it has no noise. So I am sure it is not the RCA cable that is picking up the noise.
    Also since I get no noise with just the computer and headunit, I am sure it is not my computer making the noise.

    So I guess it is my AV switcher that is causing the noise ?

    Here is how my electrical system is wired. One opus feed power to the computer, and the other OPUS feed power to the AV switcher, two video amp, and 2 Xenarc 7" LCD. They all have the same 12v source and same ground. Is there any way i could try to stop the AV switcher from picking up noise ?

    Another thing I tried is to put a ground loop isolator between my AV switcher and headunit and that didn't help either.

    Anyone know what my problem is ? Any solution ? Could it be a bad AV switcher ?

  2. #2
    Constant Bitrate CHUPACABRA's Avatar
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    Well the only way you get elecrical noise is through the RCA's or them being cheap and unsheilded.you must have some of the RCAs to close to one or more power sources.
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  3. #3
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    All the RCA are monster cable which are not cheap. With the same cable all at the same location, when I plug it into the AV switcher it has noise and when I just use a connector to connect both cable together it has no noise.

    If the RCA are picking up noise, then shoudln't there still be noise whether I plug it through the AV switcher or not ? mind you that the cable are exactly where they are as I did not move them.

    That's why I believe it's not the RCA.

    edit: I just used a ground loop isolator in between the computer and AV switcher, all noise are gone. What does this mean ? Does it mean it's the cable from my computer to AV switcher picking up noise ? bad ground ? or what ? I am trying to fix the problem thus not having to use a ground loop isolator.

  4. #4
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    Can you try using one Opus for the PC and AV (this might mean not using any screens or other components) to eliminate the possibility that the Opus' are causing it. Ground loops are a pain to track down.

    Did you also try and put the ground loop isolator between your PC and your AV?

  5. #5
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    Ground loop may not be the issue here. What you need to look for is.


    1. Your audi cables should be at least 10" away from your power cable.

    2. VIDEO AND USB CABLES GENERATE A LOT OF NOISE!!! Watch out. If you run them next to your audio cables it could be a problem.

    3. Try to disconect your components one by one to find out where the problem is coming from.

  6. #6
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    I don't think it is the OPUS. At first I only used one OPUS for the computer and the car's power for other video components. It created the same noise with the AV box and none without it.

    I moved the AV box front the front of the vehicle to the trunk with all new wiring to the OPUS. Same noise with the AV box and none with it.

    One funny one is that when I plug in other source such as VCR and PS2 into the AV box it doesn't have alternator whine. There is only alternator whine when I switch it to computer. However if I bypass the AV box and go from AV box straight to headunit there is no noise AT ALL.

    I got a noise filter from radio shack and hooked it up to the AV box, no change.

    Right now I have a ground loop isolator between the computer and AV box, which eliminated ALL the noise.

    What might cause the problem? Is it my computer actaully making noise? But there are no noise from compute to headunit. I am really confused here. I have tried everything I read on the forum such as grounding the case, psu, motherboard, sound card,,etc etc etc etc and still no use.

  7. #7
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    People have a pretty poor misconception about noise radiating into RCA cables and in the greater majority of the cases it just doesn't happen. It especially doesn't happen to the point where alternator whine is prevalent at low volumes like what happens with a ground loop (which is a direct injection of noise).

    There is a mismatch between your PC and the AV unit which the ground loop isolator fixed but tracking down the true source of this can sometimes be a pretty tricky task.

  8. #8
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    I've got some bad alternator noise

    Noise, on everything. I have a head unit going with 5 rca's to a 5 channel amp. i have noise on the pc, the radio or the cd. I am sure this is a ground loop. How the heck am i supposed to fix this>? Should I ground the head unit at the place the amp is grounded? I get mixed versions of what a ground loop is. Can anyone explain in laymans terms? THanks.

  9. #9
    Maximum Bitrate Bravellir's Avatar
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    Quote Originally Posted by lookinco
    After wiring everything into my vehicle, there is noise which I anticipated. Right now I need to investigate where my noise is coming from. Here is what I have right now...........
    I would try powering the av switcher with the same PSU ( because of the ground) that powers the sound source.

    check this: http://www.mp3car.com/vbulletin/show...613#post274613
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  10. #10
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    ^ Did you read the thread at all? I already mentioned that and he said he tried it and it didn't help. He also mentioned a ground loop iso between the PC and AV fixed it.

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