preamps and power amps

Discussion in 'Amps and Cabs [BG]' started by oreopithecus, Nov 18, 2004.

  1. oreopithecus


    Nov 18, 2004
    I have two 8 ohm cabinets (2x10 @ 160 watts; 1x15 @ 200 watts) and a head that will effectively drive either, but not both (160 watts @ 8 ohms, runs @ 4 and 8 ohms). I'm thinking about getting a used Crown power amp as opposed to a new head, since the head sounds good. The head would effectively be used only as a preamp. I looked through the archives but still have a couple of questions:

    Could a crossover be used in this set-up to biamp the two cabinets? If so, where in the chain?

    Would I use a Y cable to run the preamp line into the two channels of the power amp, or is there such a thing as a bridged input?

    As it stands, I'm thinking of simply running each cabinet off the two sides of the power amp, since there is not that much difference between their wattage ratings.
  2. IvanMike

    IvanMike Player Characters fear me... Staff Member Supporting Member

    Nov 10, 2002
    Middletown CT, USA
    1st off your head can run both cabinets at the same time as the two of them add up to a 4 ohm load, so i'm assuming you mean you just want more power.
    as long as your head has a preamp out you can use it as a preamp only (if it has a solid state power section, - tube amps don't like to be run without a load). To use a crossover you would take the preamp out of your head, run it into the input of the crossover, and then run the hi and low outs of the crossover into the power amp. if you're running full range you can use a y cord to plug into the power amp.
  3. oreopithecus


    Nov 18, 2004
    Power is definitely the issue. I don't want to underpower both cabinets to the point where I have to crank the main up past 75 percent to get good volume.

    The two cabs are only rated as 8 ohm, so I assume they wouldn't be happy running at 4 or 2 ohms.

    Not to sound like a dunce, but I assume that by running both cabs off of the existing head that I'm cutting the total possible wattage to each by 50 percent.
  4. csholtmeier


    Feb 8, 2004
    omaha, ne
    I think that you misunderstand cabinet impedance (ohms). 8 ohms means that the cab presents an 8 ohm load to your amp. That is the resistance of the cab. Higher resistance in the cab means less power will be produced by your amp.

    Now take those two 8 ohm cabs, run them in series, and now your amp will see a 4 ohm load. This means less resistance and more power from the amp.
  5. The Clap

    The Clap

    Jan 5, 2004
    Scottsdale, AZ
    Remember that, in most cases, power ratings really are limits of how much power you CAN put into the cab, not recommendations for what they SHOULD be driven with. If you've used both cabs together at a show and determined that they're not cutting it, more wattage could be your answer.

    If you haven't used them together for fear of underpowering either one, then have no fear. You can use them together with no ill effect at all, and damage should only come past the point where the speakers are distorting horribly enough for anyone to hear.
  6. oreopithecus


    Nov 18, 2004
    Thanks for the help thus far.

    Any recommendations on a specific brand or model of crossover to run between the preamp and the power amp?