impedance/gain staging problem

Discussion in 'Amps and Cabs [BG]' started by Threeviews, May 25, 2005.

  1. Help me out here...

    I've just recently replaced an ailing Hartke head with an Eden D410XLT, a Crown XLS202, and an Art preamp. I'm getting some hard-to-tame overdrive and fuzz that I never experienced with the Hartke. It's a 4-ohm cab and I'm running the Crown bridged. It may be an issue of level settings on the amp...Crown states that the levels of right and left channels should (I think they even say "must") be set identically, but when I do this, I get hardly any signal at all. Uneven settings give me plenty of sound, but it's laced with the aforementioned fuzz. Is there something obvious that I am doing wrong here?

  2. Audere

    Audere Supporting Member Commercial User

    Apr 7, 2005
    South Beach, OR
    Owner: Audere Audio
    You have the 2 outputs in phase. They should be 180 degrees out of phase.
  3. Thanks for the reply, femtometric...and sorry for my ignorance here...

    but what does that mean and how can I fix it?
  4. OK...I have figured this out. Reversed polarity on one plug of a standard XLR Y-adapter, right?
  5. Generally running in bridged mode you only use 1 volume control. There's a switch to put the amp in bridge mode, the switch takes the signal from channel A, inverts the phase, and sends it to channel B. That way both channels have the same volume. Not because the volumes are adjusted "precisely".

    Also for the output, you use the 2 red binding posts to go to the speaker. NOT red and black like you do in stereo mode.

    If you feed both amp channels, get the volume set identically, and then don't switch the "bridge" switch, you will have approximately 0 output at the bridge speaker terminals, no matter how much signal you put in. If you don't get the volumes exactly identical, you will get some sort of goofy signal.

    Doublecheck your owners manual to make sure you're doing this right. Only 1 volume control should be active, the other should be ignored. And there should be a bridge switch you have to toggle on the amp somewhere, could be small/hidden so it doesn't get switched easily/accidentally.

  6. Audere

    Audere Supporting Member Commercial User

    Apr 7, 2005
    South Beach, OR
    Owner: Audere Audio
    Yes - swap one of the balanced inputs as is shown in the drawing on page 9 of your manual. Crown swapped channel 2s input.

    In general -
    Reversing the XRL input to 1 of the power amps input channels will work if you are treating the 2 channels of the power amp as independent which you are. This assumes the power amps inputs are really balanced which it should be if it takes an XLR. The Crowns spec states it has balanced inputs - so good.

    FYI - some other types of amps have switches to put the power amp in biamped mode in which case they normally look at only 1 input and internally phase invert that input to drive the 2nd channel.

    Some players feel it is critical that the speaker moves out when the string goes down, others when the string moves up. Some people do not care - most do not know.

    Depending on which channel you change the speaker direction will go one way or the other. So you can play with this if you want to experiment.