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  1. #1
    Forum Regular Registered Member
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    Please help me troubleshoot hum in Cam. Aud P500

    Got a "new used" Cambridge Audio P500 Power amp and it is exhibiting marked hum. Sounds like a quieter version of the hum a PA system gives off. Volume has no effect on it.

    The device is pretty simple: Left Right Input Output and speaker terminals.

    I think I ruled out screwing up the Input / Output side of things since I only need input from this thing and I also tried it with the Pre-Amp off and it had the same hum.

    I WAS a little confused since CA had the posts labelled in a way I'd never seen before: it was readable from both top and bottom, which makes good sense, since half the time you're hanging over your components -- but again, it's easy once you know how.

    And it actually sounds pretty good otherwise. That is to say, when I pump music through that segment of my system, it's quite nice setting aside the hum.

    Are these units susceptible of noise from the mains? There is rather a lot of junk on that one circuit.

    Any thoughts would be most welcomed. The seller, whom I trust, says there was no audible hum whatsoever.

    Thanks.

    TB

  2. #2
    Super Moderator Site Moderator JohnMichael's Avatar
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    Check to see if you have a ground loop problem. Plug the three prong plug into a two prong cheater plug and once you remove the ground you may remove the hum. Let us know if this helps.
    JohnMichael
    Vinyl Rega Planar 2, Incognito rewire, Deepgroove subplatter, ceramic bearing, Michell Technoweight, Rega 24V motor, TTPSU, Funk Firm Achroplat platter, Michael Lim top and bottom braces, 2 Rega feet and one RDC cone, Ortofon OM20, Moon 110LP/PSU
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  3. #3
    Forum Regular Registered Member
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    Thanks very much for your reply.

    I did a lot of diagnostic stuff, like swap out the cables etc., but what worked was simply moving the unit to another outlet. It's quiet as the grave now.

    Quote Originally Posted by JohnMichael
    Check to see if you have a ground loop problem. Plug the three prong plug into a two prong cheater plug and once you remove the ground you may remove the hum. Let us know if this helps.

  4. #4
    Super Moderator Site Moderator JohnMichael's Avatar
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    Quote Originally Posted by ThunderousBass
    Thanks very much for your reply.

    I did a lot of diagnostic stuff, like swap out the cables etc., but what worked was simply moving the unit to another outlet. It's quiet as the grave now.
    I am glad you solved the problem. A different outlet will also help with groundloop hum.
    JohnMichael
    Vinyl Rega Planar 2, Incognito rewire, Deepgroove subplatter, ceramic bearing, Michell Technoweight, Rega 24V motor, TTPSU, Funk Firm Achroplat platter, Michael Lim top and bottom braces, 2 Rega feet and one RDC cone, Ortofon OM20, Moon 110LP/PSU
    Digital
    Sony SCD-XA5400ES SACD/cd, Marantz SA 8001
    Int. Amp Krell S-300i
    Speakers
    Mobile Fidelity OML1's/Bell'O 224 stands
    Cables
    AQ Rocket 44's, Diamondback XLR's & IC's

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