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Driving a power amp ??

Discussion in 'Amps and Cabs [BG]' started by ElephantTalk, Mar 14, 2006.

  1. ElephantTalk


    Jan 20, 2005
    I'm in the market for a power amp. Stereo perhaps.
    I've never used one before. In reading about them I've seen some verbage that confuses me.

    'Both channels driven...'

    Assuming that I would run the power amp in bridged mode.

    Does this mean that I need to "Y" the output off of my pre-amp (one into each side of the power amp) in order to effectively drive the power-amp?


    Do I just run the single output from the pre into one side of the power?

  2. Rumzini


    Feb 14, 2004
    Jackson, MI
    When using my QSC power amp....

    It has seperate inputs for both channels. So I can run two seperat pres into it.


    Jut one pre into channel one input...then flip a couple of switches for the amp to run in parallel input mode and I can now run both channels independently from one another...say to power two cabs.


    I can run one pre into it in bridged mode, (after flicking same switches),...plug into the channel one input of the power amp and control the volume/gain with the channel one gain knob.

    I'm sure other amps vary as to how they operate, (switches and such).
  3. lug


    Feb 11, 2005
    League City, Tx
    My Mackie can also switch to mono mode that allows one input to be routed to both sidess.
  4. Passinwind

    Passinwind I know nothing. Commercial User

    Dec 3, 2003
    Columbia River Gorge, WA.
    Owner/Designer &Toaster Tech Passinwind Electronics
    You're talking about the standard rating method. It's relevant to quote power with both channels driven because the per-channel number would often look bigger if you only drive one.

    What you need to do to run in bridged mode varies somewhat from modle to model. What specific amp are you asking about?
  5. 4runner

    4runner WARNING!"WALL OF DOOM" does "exceed" 140 decibels!

    Feb 11, 2006
    Hackensack NJ,
    Hey ElefantTalk, Don't Let the terminology intimidate you. The phrase you mentioned, "both channels driven into 8 ohms",is a standard method of measuring a power amps thd [total harmonic distortion]", by the amplifiers manufacturer. The reason for this distinction,in terminology, is because testing an amps power limitations while driving "both channels at the same time" [ hence the term ],puts an added measure of stress on the amps "power supply circuitry",transformer, capacitors,...etc. When the amp starts to clip, they document the power output [wattage], and the percentage of thd at that moment. Some manufactures run tests on their amplifiers, one channel at a time to get more favorable results, for the purpose of publishing higher wattages, but they don't tell you that the amp was tested under ideal conditions. thats why it's always good to read, and compare the specs on any equipment that you buy; speakers, amps, pre-amps, what ever. Good luck
  6. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The FTC Amplifier Rule states that amp power measurements have to be done with "all associated channels driven." On a 2-channel amp, that means both channels have to be driven at full power into load impedances when measuring the power. As others have mentioned, this removes a possible hiding place for amps with inadequate power supplies that could provide adequate juice for one channel but not both simultaneously.

    The EIA power spec is much looser in this and other respects. It allows the manufacturer the option of testing just one channel at a time. Not all manufacturers who use EIA specs take advantage of this loophole, but … some do. ;)
  7. ElephantTalk


    Jan 20, 2005
    Thanks, all!

    Passin, I am looking at a QSC RMX version of some kind. Of course anything will peak my interests as long as I can look up info about it.

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