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Trying to understand ground loop in a car

  1. Jun 22, 2012 #1
    I have an mp3 player in my car and i think it is having a ground loop issue. Whenever I plug it into my cig. lighter, I could hear a whining noise. The whining noise's pitch is proportional to the engine's RPM. I'm trying to fix and understand the problem because my background is electrical
    http://img11.imageshack.us/img11/2213/drawing1tc.jpg [Broken]

    The picture above is a model of the the mp3 player and the ground loop. Is the model above accurate? Would the audio from the headphone have a whining noise that originates from the car's alternator? From my understand, the ground loop is caused by noise current flowing through Rground. Since the audio generator references the node @ Rground, the audio source picks up the noise and outputs it to the headphones.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jun 22, 2012 #2
    You could try and disconnect the alternator belt to see if the noise goes away, but I'd bet that you would still hear the noise. The wine that you are hearing is most likely from the ignition system. It could be from ignition plug wires that are starting to break down. There could be an ignition-coil capacitor that has gone south. You may need to install an ignition-coil capacitor to deal with the noise.

    Can you try another MP3 player an see if the noise goes away?
  4. Jun 22, 2012 #3
    You don't have a ground loop from the drawing. I don't believe it's ground loop problem. There only be two possible problem, first, the filtering of the 12V in the car is not good, or your mp3 does not do a good job in filtering the power supply noise.

    If you just bought the mp3, return it and get another one and try it out before thinking about fixing anything.
  5. Jun 22, 2012 #4

    jim hardy

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    Search on terms "Alternator Whine" . The noise more likely coming in on the power lead.

    any electronics made for an automobile needs to filter its input power.
    The car alternator might put out a hundred amps of rectified three phase which modulates the battery voltage. It is the responsibility of every device in the car to deal with it.
    Radio Shack used to sell inline power filter - basically an inductor-capacitor combination.

    If you're handy with tools you might be able to pillage the part from a junked car radio and mount it in a cellphone power plug, check thrift stores nearby.
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