Ground loop type hum with strange reaction

Discussion in 'Home Theater Projects' started by Stephen Hopkins, Feb 19, 2005.

  1. Stephen Hopkins

    Stephen Hopkins HW Reviewer
    HW Reviewer

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    My current subwoofer is an original AV12 driver in a 5.35 cu ft enclosure tuned to around 22hz. It's powered by a PE 272W plate amp mounted externally in its own box. Cabling is a 30ft run of Canare L5-CFB w/ RCAP connectors.

    I've recently (the past week or two) developed a slight hum with sounds like what would normally be diagnosed as a ground loop hum. It can be remedied with moderate success by wiggling the input cable on the amplifier end but always comes back within 10 - 30 min (some times it takes alot more wiggling than others). The hum, however, is still present with the input cable completely removed. With the input removed I can make the hum go away by touching the amp plate near the input plug but it comes back as soon as I remove my finger. The strangest part is that I can always make the hum go away by lightly tapping on the cone of the driver.

    It sounds like an amplifier problem since the hum is present with the input cable removed, but I don't understand why tapping the cone of the driver consistently makes the hum go away?

    Anyone have any ideas? Thanks [​IMG]
     
  2. Dan Wesnor

    Dan Wesnor Second Unit

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    Sounds like something is loose in the amp. Tapping the driver sends a small electrical charge back through the amp, which may have some electrical effect, like discharging a cap.
     

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