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  • Ground loop problem.....

    I've just been hacking my system together in the last couple of days in order to have a computer for the trip to Bimmerfest next weekend. I'm almost positive the ground loop problem isn't coming from my audio system. The grounds are VERY good an all in one spot. I can disconnect the audio from my laptop (temporary) and the whine goes away. But as soon as it's connected it's there. it doesn't matter if I have the laptop running off the battery or off the AC converter. How can a ground loop come from an isolated battery powered laptop?

    Anything anyone can suggest I try? I leave for Bimmerfest in two days early in the morning. That means I only have tonight and tomorrow night to get this fixed. Please help.
    Matt Atkins
    Seattle5s | President
    '01 M5 Lemans Blue/two tone black and silver interior
    Factory nav.... for now

    Old Car (almost sold)
    '98 540i-6 blk/blk
    Dell 300m | Xenarc 7" | Road Runner | iBusCOMM | NaviVoice | Streets & Trips GPS

  • #2
    Does the whine you hear sound like alternator noise, or switch noise (Alternator noise will change pitch when the engine is rev'd)? Are you using shielded cable for your audio cables. You might try re-routing your audio cables and see if the noise changes or goes away. If your system allows, you could try a very short audio cable to connect your laptop to your amp, and see if the noise changes. A separate ground from the laptop case to the AMP case, or the battery negative terminal might also help. You could also turn the volume controlls on your laptop mixer all the way up so the noise gets pushed into the mud. These types of issues can be hard to isolate.

    Hope that helps
    Walt
    Walts DC DC ATX Power Supply

    Comment


    • #3
      Thanks for the reply Walt,

      It's Alternator whine. The RCAs are mid level monster cable, so they should be plenty shielded. I made sure to run the power wires one one side of the car and the RCAs on the other (well, actually down the middle. The only time they get close is at the amps which because of the location is unavoidable.

      The only thing in my audio system not grounded to the same point as everything else is my capicator and the factory deck (I have it plugged into the Aux input on my EQ in the trunk). I'm going to reground the capacitor tonight and disconnect the factory radio. I'd ground the capacitor to the same point as everything else, but then the ground wire would be very long and I've been told that can cause ground loops as well. I could relocate it, but that would require more time than I have. Maybe after I get back from Bimmerfest.

      I guess I'm just really confused as to why I don't hear the whine when I unplug the RCAs from the laptop (RCAs running to a headphone conversion splitter... thing) If I was getting feedback when only plugged into the AC converter, I might understand.. but even when the laptop is running off batter power I get the noise. I thought I understood ground loops... but I guess I don't really.

      bad gound loop, bad

      -Matt
      Matt Atkins
      Seattle5s | President
      '01 M5 Lemans Blue/two tone black and silver interior
      Factory nav.... for now

      Old Car (almost sold)
      '98 540i-6 blk/blk
      Dell 300m | Xenarc 7" | Road Runner | iBusCOMM | NaviVoice | Streets & Trips GPS

      Comment


      • #4
        From your description, it sounds like there is noise on the ground wire to your laptop. Most likely the audio outputs on your laptop have the outer conductor connected to the Laptop's Chassis Ground. That is easily verified with a DMM, just do a resistance check from the outer conductor to the ground. As soon as you connect your audio cables, you tie the shielded audio ground on your audio cable to the chassis ground through the laptop. The noise on the ground is now running along the outer shield in your audio cables, and introducing the noise. You might try a separate ground right from the negative battery terminal to the laptop ground. These types of problems can be a nightmare.

        One of these gadgets might help as well. Walt
        Walts DC DC ATX Power Supply

        Comment


        • #5
          Ok. so last night I disconnected the factory system from the EQ and the whine went away about 90%. I can only hear it very faintly when I rev the engine high and there is no music playing. That won't bother me, but I eventually want it all gone. I regrounded the capacitor and that didn't seem to do anyting. I'll do more troubleshooting when I get back from Bimmerfest and put in the perminant computer. If it does have to do with the laptop, I don't want to bother with it seeing as it will go away soon.

          Thanks for the help
          Matt Atkins
          Seattle5s | President
          '01 M5 Lemans Blue/two tone black and silver interior
          Factory nav.... for now

          Old Car (almost sold)
          '98 540i-6 blk/blk
          Dell 300m | Xenarc 7" | Road Runner | iBusCOMM | NaviVoice | Streets & Trips GPS

          Comment

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