Re: Alternator whine from A/D/S/ P840 amp (archive)

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I would suggest that you first try a better ground than the factory harness. A good AWG#10 to the chassis will help. Second, make sure you go through the level setting routine religously. Essentially, turn all the P840 input levels all the way down. Put something "typically" loud in the CD player and crank up the BMW head unit all the way. Go to the front channel level controls on the P840 and gradually increase them until you juts get to the point where you get detectable distortion from the front speakers. Then turn the radio down to a comfortable level for the rest of the process. Next bring up the rear channels so that the front/rear balance is right, and finally bring up the sub levels. When this is done, you will have the minimum input sensitivity that still provides the full uptput capability of the amp. This will minimize yet you will still get all the undistorted power the system is capable of. Essentially what you are doing in the first adjustment step (with the radio turned all the way up) is the audio equivalent of calibrating accelerator cable so that you reach full throttle with the pedal floored instead of depressed partway. If you had the accellerator cable set up so that it was full throttle only halfway down, it would sure "feel" responsive, but you really would not have any more power from the engine (as you would find when you tried to floor it and it didn't go any faster than it did halfway). Same goes for the amp, you don't need to reach full output with the volume control at less than full, and you'll get lower noise and distortion if its calibrated conservatively. The amp comes out of the box adjusted a little high for the output level of the BMW radio, so its possible that there is just a bit more gain than you really need, exacerbating the whine problem.

Best regards,
Bob Hazelwood
Product Manager, Cambridge Soundworks (yeah, ex. a/d/s/)
'93 525i 5-sp. Sharked, BL/ss'd, H&R + Bilsteins
BMW CCA (Boston)

: I installed a new P840 amp last night on my 528i using the factory wiring...I get a minimal whine from the speakerswhen I rev the engine..

: What are the common things to check to get rid of the noise??? The only new wiring I put in was a lead from the battery..all other wiring is right from the factory Amp....Maybe I need to ground it better by using my own ground wire attached to the body of the car??

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