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Thread: HELP: Ground Loop Culprit

  1. #1
    Constant Bitrate doublet's Avatar
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    HELP: Ground Loop Culprit

    Excuse my noobiness about car audio but I've done the searches and read the FAQs but I can't find a solution to the problem I'm having. I can't find where the ground loop is coming from. When I turned on the ignition, there is a small delay before my PC is turned on. During the delay or when I manually turn off the PC, the whining noise is most apparent. It's definitely alternator whine since it increases when I accelerate. The whining noise is greatly reduced when the PC is turned on.

    So I'm thinking the amp is creating the noise when it's not receiving any audio signal. My amp and PC are grounded at different spots, since my PC is in the front and amp is in the trunk of the car. Ground cables are relatively short. I've tried a ground loop isolator but it's no help. All connections are good.

    Does anyone have any idea on where the source may be and how I can fix this? It's driving me mad.

  2. #2
    MySQL Error soundman98's Avatar
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    short grounds really won't make too much of a difference, i would recomend trying to ground the setup in the same place, or run a ground wire back to the battery.

    i am having a very similar issue, i have a post that is probably on the same page as this thread, so look there for some other trouble shooting that you can try (i am planning on rewiring my setup in the very near future, so i have been dealing with it for now)

  3. #3
    Constant Bitrate doublet's Avatar
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    From what I understand from your other thread, I think we're actually having the opposite problem. The noise is only present when your PC is on while mine is most apparent when mine is off. I do hear a little hum when mine's on but when it's off, it can get pretty annoying. I was hoping I'm missing something minor so I wouldn't have to do all the rewiring.

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    MySQL Error soundman98's Avatar
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    have you tried grounding the shield of your rcas? this will sometimes work to get rid of noise, but in my problem, made it worse.

    my problem is that it will whine only when the factory circuits are energized- carputer on or off-- as long as i leave the key in acc(only the carputer, stereo system on) there is no whine(my main power run is on top of the factory wire loom going to the back of the car, so this could be part of the issue).

  5. #5
    Constant Bitrate doublet's Avatar
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    Can you elaborate on what you mean by grounding the shield of the RCA's?

    I believe reason why you're not getting any whine when you are in ACC only is because your alternator is not actually running. Mine is the same way -- if I don't turn my engine on (ACC only) there is no whine. But when my engine is running and my PC is off, the whine is very apparent. And then when the PC is actually on after the SDC delay, the whine is decreased dramatically.

  6. #6
    MySQL Error soundman98's Avatar
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    mine will whine only when the key is to the 'run' position(when the engine computers are getting power), it makes no difference if the engine is on or off, but if it is running, it will also get alternator whine.

    for grounding the shield of the rcas, take a small peice of wire and attach it to the outside metal part(shield) of the rca, and then attach it to the closest ground.

    i ususally do it right on the amps-- with everything running, you should be able to notice a immedeate difference, wether it works or not.

  7. #7
    Constant Bitrate doublet's Avatar
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    I will give that a try. Thanks, soundman.

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    Vendor - C&C CUSTOMS CabeSipes's Avatar
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    I am having the same issue with my alternator whine. I have rewired and regrounded every component 3 times and its still there. Having done so many cars I am getting very frustrated that I cant fix my own. I never had an issue with my previous system that had a headunit so I know the computer is the problem I just cant get it to stop. It is especially bad when I tether my phone to go online. I can hear the data stream from the computer in my subs.
    Going to try another ground tomorrow but that will be number 4 and doubt it will fix it. Im figuring its an isolation issue in my pc that is allowing induced noise into the audio out of the computer.
    Google my name if you need to know who I am.

  9. #9
    Constant Bitrate sergatiuk's Avatar
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    how do you deliver power to the PC ?
    inverter ? PSU ?

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    Vendor - C&C CUSTOMS CabeSipes's Avatar
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    M2-ATX power supply
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