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Buzzing in QSC or preamp.

Discussion in 'Amps and Cabs [BG]' started by Dan1099, Sep 7, 2005.


  1. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    I run a BBE Bmax-T into a QSC PLX-1602 in an SKB 4 space rack (not the Roto, but the standard one). Just recently, like within the past few weeks, I've noticed a very loud mechanical vibration coming out of the rack unit when i play with it sitting on top of my cab. I took the whole rack apart, put everything back in, and made sure all the screws on the rack were VERY tight. Alas, I've still got a buzz. Anyone have any ideas on what could be doing this, or how I could fix it?

    I mean, I know I could just Isolate it with a gramma pad or a thick towel or something, but I want a way to really fix whatever is buzzing, not just a "band-aid" if you know what I mean.
     
  2. Power transformer "delaminated"? The thin metal plates in between the windings are loose?

    Mechanical, not electrical buzz, right? Not to many potential suspects there... Fan with a chipped blade, so its out of balance?

    Randy
     
  3. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    Mechanical, for sure. And it's obviously from vibrations being transferred through the cab. I may just have not noticed it before, as there is a whole lot of vibrating going on in that room when I play to begin with. But this is definitely coming from the rack/components IN the rack.

    Edit: I should add, there items are all less than 6 months old, and have been gigged < 10 times.
     
  4. Quality

    Quality

    May 7, 2003
    Long Beach, CA
    Take everything out of the rack and run it separately, that way you might be able to isolate it to the component better than just having everything in the rack?
     
  5. Steve

    Steve

    Aug 10, 2001
    Myself and a few others have have issues with the air ducts and circuit boards vibrating loudly in the PLX's.....

    It's an easy enough fix.
     
  6. Not the first time I've heard this. Aparrently it's a spotty problem reported by some PLX owners but QSC hasn't been able to recreate the problem in the lab.
     
  7. Jim Ingraham

    Jim Ingraham

    Nov 14, 2002
    Shillington
    whats the fix???
     
  8. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I too have a "singing" PLX... I remember reading a thread discussing the fix, but I forgot what it is...

    So, I'll second the request for more info...

    It's odd that QSC can't duplicate the problem...maybe they're using a Terra Labs power cable and that solves it... :eek: :bag: :D
     
  9. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    There's an air duct, made of thick fish paper, over the heat sinks. If the sides of the duct are vibrating against something, like the capacitors or whatever, wedge some weatherstripping foam or something similar into the gap between them to stop the vibration.
     
  10. Jim Ingraham

    Jim Ingraham

    Nov 14, 2002
    Shillington
    ah... thanks
     
  11. I would still recommend at least some Mopads underneath your rack case. Good for protecting your gear from constant vibration as well as taking care of the rattle.

    I have a PLX 2402 - had the same problem. Bob told me about the weatherstripping, and I did that (thanks, Bob). However, that did not completely eliminate the rattle (and I did a pretty thorough job with the weatherstripping). I put two Mopads underneath the rack case, and the problem is gone.

    In addition, I put a 3/4 inch layer of high-density foam between the 2x10 and the 2x12, and I additionally put a Gramma pad underneath the 2x12.

    BIG difference in sound and EQ...very punchy and tight at every venue.

    Just my .02 worth,
    Jay
     
  12. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    Bob...
    Sounds like something I could handle myself without much of a problem. One question though, will doing this cause me any warranty trouble in the future?
    Thanks a ton
    Dan
     
  13. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Not at all, unless you go messing around with other stuff inside. ;)
     
  14. Dan1099

    Dan1099 Dumbing My Process Down

    Aug 7, 2004
    Michigan
    Sounds good. I'll check it out this weekend. Thanks Bob.