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"Test Driving" power amps

Discussion in 'Amps and Cabs [BG]' started by Chris Fitzgerald, Nov 26, 2002.


  1. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    I'd like to check out some power amps to drive my EA cabs to see if I might want to go in the preamp/poweramp direction for my rig. I've been using an AI Clarus to drive the cabs and am happy with the sound but the power is a bit short. My question is, how can I use the Clarus to act as a preamp when I "testdrive" poweramps? How would I make the cable connections? Line out? Effects send? I know nothing, so no answer is too basic, thanks.
     
  2. JMX

    JMX Vorsprung durch Technik

    Sep 4, 2000
    Cologne, Germany
    Line out, preamp out and (serial) FX send are virtually identical in their functionality.
    Use either line or preamp out, you can use the FX send too.
     
  3. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Thanks! How can I tell if the preamp puts out enough juice to really drive a poweramp properly? I've read so many stories on the board about people thinking their power amps they just bought are wimpy when the problem was really an "impedance mismatch" between pre and power amps. Any advice appreciated.
     
  4. lamarjones

    lamarjones Supporting Member

    Aug 27, 2002
    Raleigh, NC
    if there is an impedence mismatch, what can you get to rectify it?
     
  5. 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
    It's got nothing to do with "impedance mismatches" and everything to do with signal level.

    If the preamp can put out at least about 1.5 to 2 volts RMS, it can drive almost any pro power amp anywhere. You just have to tweak gain settings for each matchup.
     
  6. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    Any output marked "line out" should be a line level. It should be plenty. If you have the manual or can find the specs online, you should be able to find the output and compare it to the required input specs of the power amp.

    As for the other question, the easiest way to retifiy an "impedance mismatch" (really a low signal), you can stage any effect that has output gain (preferably controllable) between the pre and power amps. An EQ works well. I always suggest a compressor, as you can usually use one anyway.

    Chas
     
  7. The problem's not with an impedence mismatch. You actually want an impedence mismatch between the preamp's output and the power amp's input, with the preamp output having a lower impedence than the power amp input, but I digress...:D The question is whether the preamp can put out a high enough voltage to drive the power amp to full power. The XLR out on the Clarus has a nominal level of +4dBu so it should be easily able to drive any power amp to full power. The nominal level for the FX send isn't given in the spec but I'd be surprised if it was less than +4dBu. You should be able to drive power amps adequately with either.
     
  8. Chris Fitzgerald

    Chris Fitzgerald Student of Life Staff Member Administrator

    Oct 19, 2000
    Louisville, KY
    Thanks everyone for the helpful replies. The "impedance mismatch" misconception only goes to show ONCE AGAIN why I should stick to playing bass and not stick my nose too far into the techie stuff. :)
     
  9. lamarjones

    lamarjones Supporting Member

    Aug 27, 2002
    Raleigh, NC
    Amen!!!!

    So, if you had a low signal output, what could you get to rectify it?
     
  10. 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
    No, by all means stick your nose into the techie stuff and learn all you can! The better you understand your equipment, the easier it'll be to set up, troubleshoot, evaluate, and play. Rock on!
     
  11. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    you can stage any effect that has output gain (preferably controllable) between the pre and power amps. An EQ works well. I always suggest a compressor, as you can usually use one anyway.

    Chas