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Thread: iPhone ground loop: charger --> USB --> line out --> head unit --> ground

  1. #1
    Constant Bitrate
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    iPhone ground loop: charger --> USB --> line out --> head unit --> ground

    I just installed a new iPhone 4 setup in my jeep (otterbox based custom windshield mount for GPS, music and to shoot video from the windshield while offroading) and have a noise issue during ipod playback. I have a dock connector cable that splits out to usb (for charging) and an 1/8" line out (legit audio line out, not from the headphone jack). My charger is hardwired behind the dash and while trying to find the problem I discovered it stays powered on even when I completely disconnect the ground for the charger and it dies if I unplug USB going to the phone. So, the charging circuit is grounding through the iphone cable, back down the audio line and through the head unit, causing the noise. No matter where I ground the charger it wants to ground out through the audio line. I also tried a Griffin PowerJolt charger plugged into the cig lighter (on it's own circuit) and the setup still grounds through the audio line. Any ideas? This is only temporary while I put my carputer together but I'd still like it cleaned up!!

  2. #2
    MySQL Error soundman98's Avatar
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    have you tried to ground the power adapter to the radio?

  3. #3
    Constant Bitrate
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    It is currently grounded to the radio ground. Are you saying to ground it to the radio chassis?

  4. #4
    MySQL Error soundman98's Avatar
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    the radio ground was my first idea, but yes, it might be worth attempting to ground to the radio chassis, as that should be closer to the ground potential of the 3.5mm jack.

  5. #5
    Newbie
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    I had this problem when using my DroidX to my stereo with an aux stereo cable at the same time that I had it charging in the car. I was able to find a ground loop isolator on Amazon (http://goo.gl/nz81u) for under $5. I'm a pretty avid electronics guy, and i had considered making my own out of parts laying around the house, but I figured i'd save myself a couple hours of time for as cheap as it was.

    I got this about a week ago, and it works great.... no more noise at all. Now if i could only find a receiver with a rear aux input, so i can keep my dash looking a little less cluttered...

  6. #6
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    dependinhg on the noise, its not ground issue... could be the dc-dc converter in the chargers
    coming into the audio... its all about quality of design on the audio section of the device (input side, which is what a pc?? haha thats not made to be in a car)
    and dont frett it, get a good isolation transformers and be done

    on ebay...
    http://shop.ebay.com/i.html?_nkw=ipo....c0.m270.l1313
    -Thanks
    Mitch
    www.rush2112.net

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