Question about Kenwood KDC-MP735U CD Player

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Whistling when i start my truck, a high-pitch whistle comes out of my front tweeters. i have a factory bose system and i upgraded the headunit to the kenwood kdc-mp735u and a PAC interface, c2r-gm24. the bose has a built in amp. the whistle seems to be in-tune with the rpm's, like it goes up and down with the rpm's. what is causing the problem and what is the solution?

Posted by rupert farnsworth on

  • rupert farnsworth Aug 03, 2007

    ive tried grounding it in different places, that doesnt seem to help. what is the B+ wire?



1 Answer

Louie Role

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Hi, A couple of possible cause: 1. alternator whine - installing a filter (capacitor/inductor) in series with the B+ line to all the electronics units; 2. grounding - possibly insufficient grounding considering that you gave different brands and are interconnected; check/improve grounding, It is also helpful to install a unit chassis mounted grounding to all the units going to a common ground lug; 3. audio line level input wire too close to a B+ line - move further apart or improve shielding of signal wire; 4. loose battery connection - (although unlikely) worth to check; 5. power on line (sometimes color yellow sometimes blue) - needs filtering (a possibility only but worth to check by connecting to mains B+ instead of via ignition switch. of course this will defeat ignition switch activation of unit) A reminder, pls make sure your voltages match up chances are your electronic units are 12 volts and your truck (big truck?) might be, just might be 24. It is another issue when your truck is 24 and your units are 12, If so check your 24 to 12 DC to DC converter. Hope this gives you some idea and work out for you. pls post again how things turn up. Good luck and kind regards.

Posted on Aug 03, 2007

  • Louie  Role
    Louie Role Aug 03, 2007

    Hi again,
    B+ line is the main (usually big red wire) supply of your units. Chances are it is directly connected to your battery positive pole via a fuse. Tracing/checking where this wire leads to will help you find out any loose connection. For example from your amp or stereo, this wire will pass a fuse holder, then ontowards a junction box or where all the other wires meet, then it will either go to the ignition switch of your truck or to the engine compartment, there it will go to a fusible link before finally to the positive terminal of your battery (assuming 12v).
    Off hand, experience has taught me that this kind of noise is alternator whine which can be resolve by installing an electrical/electronic filter to remove any noise in the B+ line.
    If the whine is both present in either FM or CD mode, then big chance it is B+ noise, if it is only during FM, you might as well check your antenna grounding.
    Pls post again how things are and/or if you need further information.



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