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  • How to ground a macmini for carputer?

    Hi,

    Sorry if it sounds stupid but i was wondering on how to ground my macmini?
    I am trying to resolve the whining noise when my mac volume goes higher than 50%

    Right now what i am using
    18.5v 4a power supply
    3.3k resistor tapped to isense

    my other alternative is to have a ground loop.

    Thanks!

  • #2
    Forget grounding and get a ground loop isolator. Something like this: http://www.radioshack.com/sm-see-all...i-2062214.html (I know this particular one is out of stock).

    Comment


    • #3
      Originally posted by Jirka Jirout View Post
      Forget grounding and get a ground loop isolator. Something like this: http://www.radioshack.com/sm-see-all...i-2062214.html (I know this particular one is out of stock).
      thanks Jirka.
      appreciate the quick response.

      Comment


      • #4
        Ground Loop Isolators are really just bandaids (and still don't always fix the problem). Go after the real culprit and try grounding the system first. I can't offer any info as to where at on the minimac to attach the ground to as I don't have one, but attaching to metal on the chassis, say a screw that goes from the case to the motherboard mount or something similar should be good.

        A great guide written by a member here
        Induced noise/Ground loop trouble shooting guide.


        Good luck and Cheers

        Comment


        • #5
          I wouldn't be looking at the mini, but more the audio you have fitted in the car....!!!

          It is very unlikely the signal is bad coming out of the mini...!

          Check it by running computer speakers plugged in while in the car on the drive and if it whines then it is the mac, if it doesn't then it is the audio....!
          CLICK ME

          Smart Car due for completion beginning of march....

          Log with pictures to go online shortly after.

          Comment


          • #6
            Originally posted by www.workingcars View Post
            Check it by running computer speakers plugged in while in the car on the drive and if it whines then it is the mac, if it doesn't then it is the audio....!
            Actually I found that using my iPod did the trick when I installed mine (e.g. take the Mini out of the loop).

            Given that you custom built the cable, i'm going to go with it as the first thing to look at. Either your connections aren't solid, or in striping it for your connections you've exposed it to interference by removing the shielding (maybe from your power supply itself?).

            Another idea for isolation is to run an extension cord out from the house and run the Mini off A/C. If the noise goes away, then it is your cable/power supply.

            Has this power supply been involved in your audio system prior to installing the Mac? (e.g. was it driving a previous computer or something?) You might try moving it's ground wire around a bit too to see if that helps.

            -dave
            My pathetic worklog.
            CarFrontEnd (now it's own sub-forum!!!!)

            Comment


            • #7
              If you can determine the problem is in the audio end (I agree it probably is), check the following:

              - If you're using RCA's, make sure the RCA cables aren't running next to factory wiring. If at all possible move it away.

              - At the amp(s), make sure the ground is super tight to metal, you should be able to move or wiggle the ground cable. Scrap away as much paint from the ground spot as you can and use a star washer to really bit into the metal when you tighten it. Keep the ground less than 18"s.

              - Is the amp mounted to metal? try removing it if it is and put it on wood or carpet.

              - Are you also using an after market HU? Make sure it's using the factory ground in the factory wiring harness. If it is try removing the ground from the harness and ground it to the firewall or metal brace in the dash.

              - Has the alternator been replaced? Do your light flash on bass notes? May have a battery going bad, go to an auto parts store and ask them to load test it.

              HTH,
              B.

              Comment


              • #8
                thanks mate. i will try doing this 1st. appreciate ur reply.
                cheers
                cyrus

                Originally posted by W3bMa5t3r View Post
                Ground Loop Isolators are really just bandaids (and still don't always fix the problem). Go after the real culprit and try grounding the system first. I can't offer any info as to where at on the minimac to attach the ground to as I don't have one, but attaching to metal on the chassis, say a screw that goes from the case to the motherboard mount or something similar should be good.

                A great guide written by a member here
                Induced noise/Ground loop trouble shooting guide.


                Good luck and Cheers

                Comment


                • #9
                  Originally posted by cyruslow View Post
                  thanks mate. i will try doing this 1st. appreciate ur reply.
                  cheers
                  cyrus
                  Hello bro from MCS...

                  Comment


                  • #10
                    just an update

                    installed a ground loop isolator and the noise is removed.
                    however, the sound quality of the audio drops drastically. i played the same song before and after the installation.

                    guess i have to open up the mac and get do a proper grounding.

                    Originally posted by airspeed View Post
                    Hello bro from MCS...
                    hi.

                    Comment


                    • #11
                      Ground Loop Isolator is NOT a Fix!

                      Ground Loop Isolators are never the solution, just a work around. Useually sound quality will suffer when one is used in the line levels.

                      So you haven't fixed your problem, you've only patched. You may have get into the problem pretty deeply to take of the problem. You'll need to make sure ALL your ground points are solid to the body of the vehicle but scrape the paint off and use a silver screw with a start washer to really bit into the metal.

                      There will be several grounds, the following are all possible:
                      - one for the head unit
                      - Antenna
                      - where the head unit mounts to the dash if metal (EX: Shaft radio shreads touching the shaft holds in dash or din radio cage touching din opening)
                      - Each Amp ground
                      - Amp mounting location. (Do the amps mount to wood, carpet or metal?)
                      - Ground point for MAC/PC
                      - Ground for power supply for MAC/PC
                      - MAC/PC mounting location. (Do the MAC/PC mount to wood, carpet or metal?)
                      - The same of any other equipment you add to the car, ground/mounting point.
                      - If not a new vehicle you may have to clean the connections to the positive & negative of vehicle battery, follow the cables to the point they terminate and make sure those connections are still stong and clean.
                      - The factory ground cable from you battery on the car will almost certainly NOT be on barre metal, I like to remove it, grind the paint off and remount the ground. This can't hurt if you apply some kind of grease to protect the bare paint after you remount the cable.

                      Check as you make changes to see if you have helped the problem any.

                      Now you'll need an OMH meter to check for resistance. Check the meter leads first to see what it going to be in the leads. Set the meter to OMH, should be close to 0.0, but don't touch the metal tips with your fingers while check only hold the insulated shafts. If not 0.0, the number displayed will be your zero point.

                      You'll probably need someone to assist and some long leads, maybe 20 ft., you'll want to touch one end on the batteryterminal ground and each of the ground locations we discussed above to ensure you get your 0.0 poiint or at least VERY close to it. If you find one that is significantly large this is a BIG problem and you'll need to resolve that problem. Doing this is another big process.

                      This should get you going, you may want to go to a car audio shop for all this it is QUITE involved if it's your first time...

                      Unfortunately I'll be away from my puter the next couple of days i won't be able to reply so quickly.

                      HTH,
                      B.

                      Originally posted by cyruslow View Post
                      just an update

                      installed a ground loop isolator and the noise is removed.
                      however, the sound quality of the audio drops drastically. i played the same song before and after the installation.

                      guess i have to open up the mac and get do a proper grounding.



                      hi.

                      Comment

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