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Thread: Where is this coming from?

  1. #1
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    Question Where is this coming from?

    Hey guys,

    I noticed something today. I went and disconnected the power from my PC in the trunk and I still get alternator whine in my speakers when the engine is running. I am using very nice audio cables that are running on the opposite side as power. I cna't understand why I am getting this interferance. If I unplug the cable from the sound port on my motherboard, the interferance dissapears all together. Is there something special I should be doing to the cable? I have it wired directly to my HU's AUX-IN channel. I did notice a small (what appears to just be wire insulation) hanging off of one of the cables in the pair. I don't know what that is for. Is that an extra grounding point or something? I never heard of grounding the audio wires. And my sound is on-board, not a sound card.

    Any suggestions, ideas?

  2. #2
    Maximum Bitrate binary.h4x's Avatar
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    is your metal case grounded?
    2007 Honda Fit Sport 1.5L SOHC-VTEC

  3. #3
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    thats definitely induced noise, most likely through the RCA cables, if youve isolated the computer from the charging system and still get it. heres a neat story:

    So we did a decent system in my buddies ford mustang. an el cheapo RCA cable came with his amp kit, but he wanted a second one. so he went out and spent big bucks on a mid level monster cable. payed a boatload for it, too. So we decided its gotta be the superior cable. We installed that to his soundstage adn used teh cheapy for subbass.

    well I'll be darned if he didnt have a terrible noise problem! thought about it for awhile, then decided to try something different. we swapped the cables. cheapy ran teh stage, monster ran subbass. noise went away.

    the moral of the story is that a nice cable doesnt guarantee you freedom from induced noise. Also keep in mind, that ANY source of large draw can cause interferrence! hobby installers usually say something like run the RCA's down one side of the vehicle, and power along the other. well, if you jsut happen to run your RCA's down one side, where the car ECU is, then they lay across the fuel pump, and finally acros the power wire to a stock amp, it could be miles away from your aftermarket power amp cable, it might still pick up noise!

    Also keep in mind that its not just power that you have to worry about, GROUND can cause noise too! and that one is much more tricky to figure out. it just travels across the path of least resistance through the frame. i fyour fuel pump draws ground across where your RCA cable runs, despite it being far away from power or any other large draw of power, it could still pick up noise!

    its kind of a catch 22 based on murphy's law.

  4. #4
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    Quote Originally Posted by binary.h4x
    is your metal case grounded?

    Yeah my case is grounded to the car chasis.

  5. #5
    Maximum Bitrate binary.h4x's Avatar
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    try ungrounding the case then check for noise.
    2007 Honda Fit Sport 1.5L SOHC-VTEC

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