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Thread: Engine electrical noise

  1. #1
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    Post Engine electrical noise

    I have the following problem: when the engine is running, I hear this noise coming from the speakers that changes frequency proportionaly to the engine's RPM. I know it does not have anything to do with computer interferance (Power supply, spinning/seeking HDDs, etc...), since it stops immediately when I turn off the engine while the PC is still running.
    It's not so serious, especialy when I turn the sound card's volume up, but it gets pretty annoying when I listen to some easy listening music or when I just use windows (without any music playing back).
    To send the sound to the head unit I use Sony's XA-107 source selector adapter.
    I also mentioned interferance even with the engine off, when I turn on the car's headlights (the noise does not variate though when the engine is off). The headlamps of the car are Xenon type which as far as I know have some kind of special power supply circuitry, which I suspect might cause the interferance. Also, with the headlights, the engine's diagnostic computer and the electronic odometer turns on.
    Could you suggest a cure to my problem? Some kind of filter on the aux in of the headunit?

    Thanx,
    Dimitris

  2. #2
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    That is caused by the car power system. It happens with car lighter adapters too. When the engines RPM raises so does the charge from the alternator, then to whatever powers your music. Check to make sure all your grounding is properly done. I think that should do it. I had a lighter adapter for my portable CD player and I had the same symptoms as you do. I wouldn't think the head unit would do this, I would check the source selector adapter.

    Hope this helps some
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  3. #3
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    Maveric,

    I am not using a lighter adapter. I have a line from the battery terminal straight to the PSU. The case is made out of metal and grounded. Do I have to ground the sound card's line out or is it already grounded through the motherboard?

  4. #4
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    It depends on what car you have Dimitris1976. It could be the condensor(capacitor) that is used to reduce the electrical noise created by the points in your engine. There is also a condensor on your alternator. The condensors leak and fail after a few years and need to be replaced. If this doesn't work (or if you have a fuel injected engine with no points) then you might have to use a noise filter on the power leads running to the computer.

  5. #5
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    The car is only three months old and it has a multipoint EFI engine. Are there any ready made noise filters or I have to build one myself? Do I need to install this filter on the lead that supplies power to the computer, or on the cable that runs from the soundcard to the headunit's aux adapter? What is this "ground loop isolator" that some people use? Is it gonna help?

    Please, help - It's driving me crazy now (the noise)!

    Dimitris

    [ 10-14-2001: Message edited by: Dimitris1976 ]

  6. #6
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    The noise filter will go on the lead that supplies power to the computer. You can buy them at car stereo shops usually. You might also need a ground loop isolator. It is a 1:1 transformer that you would connect between the soundcard and the aux in. They break the ground connection created by the shielding in the RCA cables to prevent a ground loop forming(a ground loop is where there are multiple ground connections between two devices. This often causes current to circulate through the grounding resulting in noise). Ground loop isolators are also available through some car stereo shops.

  7. #7
    Maximum Bitrate MikeHunt79's Avatar
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    i got the same problem as this when the 3.5mm jack wasn`t pjugged in the sound card properly.... i know it sounds stupid, but check that

  8. #8
    Maximum Bitrate PoBoy's Avatar
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    Ground it all again. Scratch off the paint from your car where you ground to. You need metal on metal. Check your RCA's too if the grounding doesnt work. I had a cheap/bad set of RCA's running to my amp and that caused some serious engine noise. Do you get noise when listening to the car radio too?? Do you have an amp?? if you do...check those RCA's (get better ones if they are cheap and you have a big system in your car) and try not to connect 2 together to make a longer one. That will not help your situation.

    Good luck, POBOY
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  9. #9
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    I don't have any noise at all when I listen to radio or CDs. I get the noise when I change to the aux in (no matter if the computer is turned on or not - the jack plugged in the sound card or not).I mention though that it's getting worst when I turn it on(the computer)! I was a little lazy when I installed the cables and passed both power and audio on the same side of the car. I'll change that immediately!
    Also, do you think it could be better if I didn't ground the audio cable on the aux adapter's side? This way I could eliminate these currents that run through the coaxial's shield when it is grounded on distant spots.
    Finally, how thick should these audio cables should be? I am usind cables that used to have at my home stereo without any troubles (at home), but they don't have very big diameter. Is there any speecial type/brand I should ask for?

    Dimitris

  10. #10
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    I instaled a ground loop isolator and ALL the noise is gone - just like that! (thanx, Technics) I didn't even had to run the audio cable on the other side!

    Dimitris

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