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Bridging QSC (exceeding recommendations)

Discussion in 'Amps and Cabs [BG]' started by MuzikMan, Apr 22, 2004.

  1. It was recently suggested to me that I can Bridge at 4 ohms with my QSC USA 900. To the best of my knowledge this amp is rated to handle 4 ohms per channel and 8 ohms bridged.

    Does anyone have any thoughts on this? What type of danger does pushing this type of load present? Do I run the risk of frying my amp or will it protect itself?

    This panel has been extremely helpful to me and I anxiously await your thoughts.
  2. 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
    The USA 900 is not ideal for bridged 4-ohm operation, but it may work. Keep these things in mind:

    Not all 4-ohm loads are alike; some are actually lower than 4 ohms at some frequencies and thus may be a more difficult load for the amp.

    Don't run the amp into clipping. If you see the clip LED flash, back off on the levels. And don't use heavy compression.

    An extra fan mounted in the back of the rack to blow air into the amp will help its cooling.

    It won't hurt to try it out—just do it before a gig, not during. ;)
  3. Thanks for the reply. It's good to know I may be able to bridge at 4 ohms, but since I'm running 2 cabs at 8 ohms each I think I'll probably stick to stereo operation. I was just curious. It seems like I would want to get the most power that I can with whatever setup I run.
  4. Doodaddy


    Jan 11, 2005
    West Monroe, LA
    I hate to bring up an old thread, but did you ever do this? I'm looking into purchasing this amp and I was thinking the same thing.
  5. I did it once successfully and once unsuccessfully. The second time I tried it it shut down after about a half hour. I haven't tried it again but I bet if I installed a fan behind it it would be more stable.

    Mine works great and I am totally happy with it. The 550 watts I get out of it in stereo mode works just fine. Just keep in mind it isn't guaranteed to work at 4ohms bridged.