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    Need help diagonising audio problem

    I've recently added a cd43 to my e30 vert, and to that an aftermarket 4 channel amp (jl a4300). Luke suggested the best way to hook the cd43 up to the amp was to wire rca cables to the headunit (i.e. positve to (+) for each channel and negative to common ground for all 4 channels instead of to (-) for each channel) and then run the rca's to the amp. This amp has input voltage ratings upto 8V and the cd43 puts out around 6V per channel.
    So, it's all hooked up and the result is good- except for a very high pitched tone coming out of the speakers when the headunit is on. This tone is in the background and is not volume dependent. This also happens when the engine is not running- so that's not it...
    I ran my audio and power cables down different sides of the car, so I don't suspect interference that way, but I ran cheap-o rca cables... could that be it? I even tried a different amp with the same result, so that is ruled out..
    Anyone guess what the problem is and what a solution would be? Thanks..

    #2
    Assuming everything is hooked up properly...
    Unplug the RCAs. If the sound disappears, you've probably discovered your problem. The only other suspect could be your gain is set too high.

    I have no idea what the hell you were trying to describe regarding how you hooked your stereo up. RCAs don't use a ground, they are unbalanced...

    I might be reading into it wrong, but I'm way confused.
    I retired my E30 for now...
    E46 323i
    David Schultz

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      #3
      Originally posted by DSchultz325e View Post

      I have no idea what the hell you were trying to describe regarding how you hooked your stereo up. RCAs don't use a ground, they are unbalanced...

      I might be reading into it wrong, but I'm way confused.
      Lol------- yeah, I know. What I did was cut one end off an rca cable. Took the center conductor and soldered it to the (+) speaker wire. Took the outside wire (shield) and soldered it to common (did this for all channels). I'm thinking I may just get a line output converter and try that- although I shouldn't really have to step-down the output on this head unit.

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        #4
        Eeek. I bet you have interference in what you just described you did. Doesn't sound real clean.

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          #5
          Originally posted by DSchultz325e View Post

          I have no idea what the hell you were trying to describe regarding how you hooked your stereo up. RCAs don't use a ground, they are unbalanced...

          I might be reading into it wrong, but I'm way confused.


          Originally posted by netcsk View Post
          Eeek. I bet you have interference in what you just described you did. Doesn't sound real clean.
          Guys, I have been installing aftermarket amps into BMWs for years and years doing just this.

          Generally, referencing input ground to chassis is no big deal. Most "unbalanced" (yeah right) simply use a small (picofarad range) cap to float the output of their deck above ground...not really using a true "unbalanced" signal at all.

          My suggestion is to find a test speaker and see if the deck is making that noise...because it sounds to me as it might be a faulty deck.

          Next, I would grab a test source, like a portable CD or an MP3 player and plug it into the amp, to make sure it is not causing the noise.

          Then, you will know what is causing the noise and further diagnostics can happen. We will then isolate the noise using whatever is needed.

          Luke

          Closing SOON!
          "LAST CHANCE FOR G.A.S." DEAL IS ON NOW

          Luke AT germanaudiospecialties DOT com or text 425-761-6450, or for quickest answers, call me at the shop 360-669-0398

          Thanks for 10 years of fun!

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            #6
            Originally posted by StereoInstaller1 View Post
            My suggestion is to find a test speaker and see if the deck is making that noise...because it sounds to me as it might be a faulty deck.
            Shit, I sure hope not. It's a brand new cd43- bought it off of ebay, #1 in reliability!

            No one seems to be questioning my cheapo RCA cables. Literally, they were $6.50 for two 24 foot cables that I cut in half. I think I will invest in some better ones and then try to rule things out-

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              #7
              If you install your RCAs close to any power wires, the really cheap ones may cause the noise you are getting. See if you can borrow a set from somebody and just throw it outside of the car to test.
              '96 328is
              '97 m3
              '04 zhp

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                #8
                Well, I got some additional advice, and hooked up the rca's the conventional way, with + to center pin connector, and - to outside connector instead of grounding all the outside connectors together to the chassis. Problem solved!

                I guess newer BMW headunits (aka CD43) have balanced output and the negative wire run is needed to counteract signals that cause noise- well, whatever, it worked and sounds amazing. No whine when the engine is running or high pitched background noise.

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