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  • Whining/Ground Loop

    argh...I'm getting the dreaded alternator whining. I've sanded the grounding area to a bright shiny sparkle, so I'm sure there's proper contact with the car chassis. My amp is definitely grounded well as I get no whining/hissing when I'm in CD or Tuner mode. But as soon as I switch my head unit to Aux-In mode...I hear that ever so faint whine. My amp and my opus are grounded in seperate locations and grounding them at the same spot isn't logistically possible. Would a "grounding distribution block" help? Any other devices to isolate the whine and kill it?

  • #2
    Measure the resistance at the grounding points. Going by theory, you should only ground devices that have resistance differences of no more than 0.25 ohms to avoid ground loops.

    In theory a grounding distro block would eliminate that, but you said it yourself, it's not possible in your case? i'm guessing they're too far away from each other?
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    • #3
      Make sure that you didn't accidentally put a screw into an RCA cable, or something like that. You say grounding your amp + Opus isn't possible... Try to connect a wire between them as a test to kill any differences in potential. Interesting article wrote about ground loops:
      http://www.epanorama.net/documents/g...op/basics.html
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      • #4
        is everything grounded to the same points? Also try to ground your computer case or motherboard to that same point
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        • #5
          THIS got rid of my alternator whine.
          MikeH

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          • #6
            and ^^"that"^^ will also cause loss of sound quality. It's a bandage to the problem, not a solution. Best thing is to ground everything to the same point. I don't see how it can't be possible (wires can be bought fatter and longer), but if it is, the resistance explanation above makes a whole lot of sense and is probably a good rule to go by.

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            • #7
              Bobby,

              I think you may be confusing ^^THAT^^ with THIS , which DOES affect sound quality. The noise filter I referred to is connected to the DC input line to your audio amp and/or CarPC and has no affect on the audio except for filtering incoming noise from the power lines.
              MikeH

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              • #8
                thanks for the input guys. actually, I CAN use a distribution block I. I reason I couldn't ground the opus to the same place the amp is grounded is because I put the amp in a while back and basically, that area is inacessible. I mean I could totally tear up the carpet and spend about several hours messing with my seats and their adjustable rails. anyhow, thanks for the info...it'll give me some things to try out this weekedn.

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                • #9
                  Hey Mike,
                  I was going to ask you to recommend something for me. Did you put one on your PC power and one on your Amp power or how specifically did you wire them up?

                  Peter



                  Originally posted by MikeH
                  THIS got rid of my alternator whine.
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                  • #10
                    Chut,

                    Here's what cured my noise problems. It took a nose filter on the +12V line and a ground loop isolator on the RCA auido lines, as well as good grounding techniques.....
                    Attached Files
                    MikeH

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                    • #11
                      Well, thats interesting!
                      I have ordered a noise filter for the positives to the amp and pc but I didn't know of a "ground loop isolator" with RCA's. The only isolator I have gets routed between the pos's for all power leads.
                      BTW...you mentioned "programming" the PS for power off of the amp. Is that something I can do?
                      Thanks,
                      Peter
                      Stop Buying New Music CD's.
                      Hit The RIAA where it lives.

                      Indash Motorized 7", Epia Nehimiah, 512 MB, 80 GB, DVD, Wireless G, XP Pro, XM PCR, Kenwwod 5 Channel 1200 Watt Amp.

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                      • #12
                        Chut,

                        you mentioned "programming" the PS for power off of the amp. Is that something I can do?
                        No. I need to modify the source code to make this mod. Sorry.
                        MikeH

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                        • #13
                          this may help, run power on the other side of the car, isolate form the rca, power should be at least 24" away, make sure you have good rca twisted pair with a good shield then run a seprated wire from your stereo case (use one of the case screws) to the computer case and then to the amp case

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                          • #14
                            dont forget your alternator may be faulty! They usually have a small condenser or capacitor on them, to smooth out the pulses from the 3 phase internal electrics! Inside every alternator, is a 3 phase alternator, which gets redtified by 9 diodes (6 power diodes and 3 supply diodes) into DC. Sometimes when the commutator rings are dirty, worn or the brushes need changing, or the regulator has a bad connection/dry soldered joint in it, it introduces the alternator whine into the rest of the cars electrics! thats why ground loops wont cure it, its in the positive power!

                            If running the rca leads down the other side of the car away from the amp power cable, and eliminating ground loops doesnt work, try getting your alternator reconditioned.
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                            • #15
                              A few things here that seem to be inaccurate.

                              1) a bad alternator wont causs alternator whine or be very noticable. a brand sparkelin new one though, will. better condition of the componants in the alternator == bigger EMI field around the alternator. If for any reasons at all you discover that the source of noise is in the positive potential of the electric system, you should read #3 below. If your car is old, getting your alternator reconditioned or a new one wouldnt hurt anything

                              2) Routing power & RCA away from each other is useless becuase the RCAs are still near a power plane, you know, the chassis of the car. This wont cause alternator whine unless there are already issues.

                              3) filters will help on the power lines of poorly regulated head units and other equipment. A good computer powersupply should not need one, however the electrical system in a car is among the worst enviroments for senstive electronics. no amount of diodes and capacitors will get rid of noise like a good EMI filter and properly shieled componants (which your computer, if not in a metal case, wont be shieled)


                              So what does cause alternator whine? a major source of it is ground potential differences in the signal between the souce and the amplifier stages. Example is that the ground ring on the output of the Computer is at a different potential (it probably is) than the input on your head unit or Amplifier. In this case a ground loop isolator would come in handy as that grounds the source to the same plane as the amp/head unit. Or you could modify the computer motherboard/connector/cable to ground the ring (sheild) to the cars ground.


                              I had a car that was plauged with alternator whine. it was not a head unit/amp grounding problem where i needed to run wires all over so everything was grounded at the amp (which didnt work anyways).

                              The EQ that i had in my system, the ring (outer shell) of the input RCA's had broken its connection to the circuit board, causing the ground loop. re-soldering this fixed the problem.
                              how did i find it? i made a set of dummy/shorting RCA connectors (two male, two female), started at the source and worked to the amp.

                              say your sytem goes.

                              computer --1--> head unit --2-> line driver -3--> EQ --4--> Xover --5--> Amp

                              If you short each RCA cable (#1 at the source end, i.e. at the computer, not after the length of cable). When it goes away, the componant before it is the source.

                              So if it goes away when you short cable #4 , the EQ is the source of the problem.

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