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QSC USA 850 problem!!!

Discussion in 'Amps and Cabs [BG]' started by pedroferreira, Sep 27, 2004.


  1. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    I'm using a Raven Labs PHA-1 driving a QSC USA 850 (bridge) to an EA Cxl 112.
    When I'm playing I notice that the sound slightly changes over time.It's like a high filter rolloff that comes and goes.It's not cyclical. It just seems "flat" and after a few moments it seems with a rolloff.
    When I play with headphones (connected to the preamp), I don't hear this effect, so I'm assuming that the problem is with the amp.
    Is this a "normal" problem?

    Is there an "easy" fix?

    Thanks in advance.


    Pedro
     
  2. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    Could this be a symptom of a bad cable (the one that goes from the pre to the amp)? :oops:
     
  3. Dont know if its the amp or not but if it is, Crown Macrotech is the way forward for separates...
     
  4. No It's not normal. Can't tell you if the amp is the problem but I thought you might want to know that QSC offers replacement and upgrade parts on almost all their amps on their website.
     
  5. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    Thank you for your answers

    I suspect that the problem is in the cable that connects the pre to the amp.
    I changed the cable today and I didn't hear that effect. But I only played a few hours.
    I have to play the next days to see if the problem persists.

    Pedro
     
  6. 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
    Let me know if the problem comes up again.
     
  7. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    Thank you for your interest.
    So far I didn't hear that effect with yhe new cable.
    I let you know if it happens again.

    Pedro Ferreira
     
  8. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    I'm afraid that the problem is still there. What could be the cause?
    How can I solve it?

    Thank you,

    Pedro
     
  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
    Bom dia, Pedro. Are there any other symptoms? How do you have the inputs and outputs of the power amp connected? Obrigado!
     
  10. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal

    Hi!
    Do you Speak Portuguese? :D

    I just notice a change in the frequency response. I don't believe it has to do with heat because it happens even when I'm playing at home at low levels.
    I'm suspecting that I'm having problems with the cables I'm using to connect the pre to the amp. I just ordered a new quality cable and see what happens.
    The problem is in that connection or in the amp. I wish it coulb be the cable :bawl:
    The pre is connected to the amp using an unbalanced cable (the pre's output is unbalanced); the amp is connected to the cab trough the binding posts output (the only output) to the speakon input of the cab, with a good, heavy gauge, power cable.

    Thank you

    Pedro
     
  11. pedroferreira

    pedroferreira

    Feb 10, 2003
    Portugal
    Could it be because I'm using it in Bridge Mode with an 8 Ohm cab???
     
  12. 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
    I know a little bit of Portuguese. My sister-in-law is from Portugal, and this past summer she and my brother and their kids went back there for a few weeks for a wedding. Her family still has a farm outside Lisbon, and they harvested and brought back some fantastic oregano. I brought some home and can't wait to try it on some food. I love good oregano.

    There isn't anything in the amp that could change the audible frequency response intermittantly, but perhaps there is some change in gain or signal level going on. That could sound like a change in low end response.

    If the input cable does not make a good connection on both the + and - input terminals of the input jack, you could get a level loss of 6 dB

    Try putting the amp in stereo mode and use one channel, then the other. If the problem is in the amp, then the odds are overwhelming that it would show up in one channel and not the other. If the problem persists regardless of which channel you use, the cause probably lies somewhere else. Let me know what you find.