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QSC PLX rattles like a box of rocks

Discussion in 'Amps and Cabs [BG]' started by Soulfinger, Jan 26, 2012.

  1. Soulfinger


    Sep 20, 2004
    Houston, TX
    I have a QSC PLX 2402 and it works great. It was considered lightweight when I bought it! If I set it on my cabs, something in it rattles horribly. This was never really a problem, because I would always my rack on a crate next to my cabs at gigs, and never really used it at home. However, in my new home studio, I really need it to be on top of my cabs, and would like to actually use it. However, it rattles like mad, even at really modest volumes. It stops if I press down on the top of the amp. Any ideas on what to do?
  2. will33


    May 22, 2006
    Take the top cover off and see that no components have broke loose and are rattling around inside. Otherwise, just make sure everything is screwed back down tight, may have worked loose over the years. A strip of felt or weatherstripping around where the top cover screws on make help keep away the rattles. Or set something on top of the amp.

    If your speaker cabinets top panel is actually vibrating and rattling the amp, you need to add some crossbracing to the inside of the cabinet to stiffen it up, it shouldn't do that. Will sound better afterwards too.
  3. JimWasHere


    Sep 8, 2010
    Portland, OR
    Look for missing or loose screws on the outside first. The pressing on top and it stops part makes it sound like it may be the case. If that doesn't do it, and you feel the need to open it up, be mindful of things that hurt to touch :p You'll probably find something rather obvious if the rattle is as bad as it sounds.
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    +1. Cabs should not vibrate. In any event some of this underneath should help:
    Walmart.com: Ozark Trial Camping Pad, Blue: Camping
  5. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    That may be totally normal, as far as the PLX.............

    IIRC the PLX have a near-zero fastener type design, where the PWB has keyhole slots in it, with only one or two screwholes.

    The keyhole slots go over special standoffs that have a groove in them. The board goes over, and then slides sideways to catch in the standoff slots. One or two screws are then put in to hold it in position.

    Bottom line is that most of the board is held by sliding fasteners that MUST be a little loose to work.

    It's a good system, actually, but can rattle in situations like yours. That's not exactly what they were designed for, they were PA amps to go in racks separate from the speakers.

    Either move the amp, or possibly dab some silicone or other removable dampener material on the slotted standoffs. For silicone, you should use the type safe for electronics.....
  6. Soulfinger


    Sep 20, 2004
    Houston, TX
    Interesting thoughts on the construction of it. I know plenty of players (and I'm sure there are many more here on TB) that have used these amps on top of their cabs. There is certainly nothing wrong with my cabs, and the amp does this sitting on any of them. I'll pop open the hood and see if there's anything obvious going on, without trying to fry myself. If that doesn't do it, I may take it to the amp doctor.
  7. gregbackstrom

    gregbackstrom Supporting Member

    Feb 3, 2005
    Tacoma, Washington
    Hi Soulfinger,

    I have the same amp and the same problem -- lots of folks complained about this when these amps were new. I improved the rattling somewhat by putting some thin foam insulation around the "fishpaper" fan tunnel that directs cool air within the amp. I also lined the inside of the top cover with additional thin foam. The pressure that the foam put on these loosely-mount parts got rid of MOST of the rattles. But not all ...

    I finally mounted the amp in its own two-space rack case, and now I set it vertically beside my cabinet when I use it (which is infrequent).

    Great amp, but as Jerrold pointed out, it was designed with a lot of loose parts.

    Although this
  8. Soulfinger


    Sep 20, 2004
    Houston, TX
    Thanks for the info. I can't believe I hadn't heard about this before.

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