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Subwoofer thumping continuously

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  • Subwoofer thumping continuously

    Hey there, its been a long time since I've posted on here but back when I used to mess around with amp ampage was always the most helpful place so I thought I'd give you all a go!

    I have this MJ Acoustics Reference 1 MKII subwoofer and recently its started acting up. When I turn the amp on, as usual it will take a second to come on (caps charging up or whatnot), and once the relay kicks on normally the amp is good to go. However, all of a sudden now once the relay kicks on, I hear a loud popping or thumping noise, like in-rush current but just over and over again, fast, I'd say about 3-4 times a seconds. It happens regardless of whether or not there is any input signal, and even when there is I can't hear anything but the thumping.

    I've taken the amp out and looked at it on startup to see if its the relay just clicking over and over but its a see through housing and I can see it click, make contact, and stay there. I did notice that the board is a little discolored around one of the IC's, its a TI NE5532P opamp. The filter caps don't look bulged and aren't leaking, nor are any others...

    Any ideas folks? I do have a scope if that helps, haven't used it in ages but if you've got any ideas shout at me!

  • #2
    It's called motorboating. Probably time for a recap and a check of the subwoofer PA power supply.


    • #3
      My guess is that it is cycling trying to protect itself. Power up- fault sense- try again- fault sense- try again- fault sense, rinse and repeat. I would first check for any shorted output devices in the power amp.
      "Yeah, well, you know, that's just, like, your opinion, man."