USA 850

Moderators: Cameron Shoffner, Christian Cook, Kirk Fyvie, Martin Barbour

Mon Jun 09, 2008 11:58 am

  • I have a USA 850 which I had not used in about 3 years, prior to that I used it in stereo mode. I took it out yesterday and hooked it up in bridge mode. It still sounds good but the clip light on channel 2 is lighting up, The gain knob on Ch 2 is at zero, when I turn up the gain on Ch 1, the volume fades in and out. I want to start using this amp again in bridge mode to run one Cerwin Vega speaker(PD-18C)with a rating of 300 watt continious @ 8 ohms. Please help
    Rasta
    rastadaley
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Mon Jun 09, 2008 12:27 pm

  • Hi Rasta,

    Check here for a list of US service centers. If you can't find a service center convenient to you, please call QSC Technical Services at 1 800 QSC AUDIO for an RMA to send the amp in for factory service. Thanks!
    Bob Lee
    Technical Communications Developer
    QSC Audio Products, LLC
    Past Secretary, Audio Engineering Society
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    "If it sounds good, it is good." —Duke Ellington
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    Bob Lee
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Tue Jun 10, 2008 5:55 am

  • You has not said what you think is wrong with it, when I had stopped using the USA 850 amp, it had no problem, now that I want to use it again the clip light on Ch 2 is lighting up. I don't understand why because I am using bridge mono mode which should make Ch 2 inactive, and the gain on Ch2 is at zero. The Ch 1 gain knob also makes the volume fades in and out but does not increase the volume, I have to use the mixer to increase the volume. I don't have these problems with my PLX and PLX2.
    Rasta
    rastadaley
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Tue Jun 10, 2008 6:13 am

  • Channel two WILL be active, you are strapping the 2 amps inside the box together, does it work properly in stereo? can be some capacitors inside that did dry out or leaked can be many thing without benching the amp hard to say.
    Stephane Levesque
    Stephane
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Tue Jun 10, 2008 4:19 pm

  • The amp really should be examined by a service technician to determine what's wrong with it.
    Bob Lee
    Technical Communications Developer
    QSC Audio Products, LLC
    Past Secretary, Audio Engineering Society
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    Bob Lee
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Mon Jun 16, 2008 7:11 pm

  • I had the amp in the shop and got it back today and was reading the manual before putting it back into use. I want to operate it in bridge, running only one 8 ohm speaker (Cerwin Vega PD 18C) that is capable of 300 watts continous. The USA 850 manual say to connect only to ch 1 input for bridge operation, does that mean I should connect both channel from the mixer to channel 1 on the amp. I thought that in bridge mode both channel of the amp operates but is control by ch 1, so channel 2 should needs a signal going into it. I have a Y cable to connect both channel from the mixer to ch 1 of the amp but will wait for your response before doing it. thanks
    Rasta
    rastadaley
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Tue Jun 17, 2008 9:26 am

  • In bridged mono, the amp needs only one input, connected to Ch1 input. Note that as pushing the Stereo/Bridge switch to Bridge, it will automatically feed a required signal (from Ch1) to drive Ch2. So you should not feed any signal into Ch2 input and turn Ch2 gain control fully down. Use your mixer to combine all signals to one prior sending it to the amp’s input.
    Thanh Nguyen
    Service Development Engineer
    QSC Audio Products, LLC
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    Thanh Nguyen
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