How to hook up a stereo amp for mono?

Discussion in 'Pro Audio' started by Adam, May 1, 2006.

  1. Adam

    Adam Guest

    Hello everyone, I have a simple problem. I have a McIntosh 2200 amp
    (200 W/ch, 400 W mono), with which I am driving a large center channel
    speaker (4 ohms). The Mac has L and R sets of outputs, each consisting
    of a "COM", 1 ohm, 2 ohms, 4 ohms, and 8 ohms. There is a switch on
    the back which allows you to toggle between MONO and STEREO output. I
    turned this to MONO, and originally hooked up some speaker wire to the
    R outputs only (4 ohm on amp to red on speaker, COM on amp to blue on
    speaker).

    Things sounded fine, but I wondered if I was getting the full 400 watts
    of power I was supposed to be getting, when the amp was functioning as
    a monoblock. After all, I had to crank up the R/MONO gain to the "3"
    position (75% of max) in order to get sound as loud from the center
    channel as from my stereo speakers...and they are being driven with 300
    W/ch. Then today, after cranking a surround sound concert DVD at high
    amplitude for about an hour, I felt the backs of the two transformers
    in the amp. The right one was hot, but the left one was cold. Now,
    I'm starting to think that the wires to the speakers are not hooked up
    right.

    Consulting an instruction manual for another Mac amp (not a 2200), I
    try hooking up one wire to the 4 ohm L output, and one wire to the 4
    ohm R output. I turn up the gains, no sound. I try reversing the L/R
    polarity on the speakers, still no sound.

    Does anyone know what I'm doing wrong? I'm pretty sure the amp works
    fine, because I listened to it extensively at the house of the guy I
    bought it from. He wasn't exactly sure how to set it up as a monoblock
    either, though.

    Thanks, Adam
     
    Adam, May 1, 2006
    #1
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  2. Why are you asking us and not McIntosh?

    By the way, an amplifier's power rating has no relation whatever to how loud
    it plays at a given setting on the control center.

    If you connect anything to two identical voltage sources, no current flows,
    because there's no potential difference.

    Pick up the phone. Call McIntosh.
     
    William Sommerwerck, May 1, 2006
    #2
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  3. Adam

    Mike Rivers Guest

    You really need to look at the manual for that amplifier or at least
    ask McIntosh. Does it say anything on the chassis about connecting a
    speaker for mono operation? There might be a diagram. Do you also get
    output from the Left speaker terminals? If so, I suspect that on this
    model, the Mono/Stereo switch just combines the inputs, and the outputs
    are independent - so you're still getting only 200W into your speaker
    from one channel.
    This is completely irrelevant. Sensitivity of speakers varies widely.
    This pretty much confirms that you're using only one channel.
    This is what's called a "bridged mono" connection. With this
    configuration, you connect a signal to one channel input. It gets split
    into two paths, one going straight through the channel, the other being
    inverted in polarity and going through the other channel. When you
    connect the speaker between the "hot" side of both channels, you are
    essentially putting both power stages in series, and the current from
    both amplifiers flows through the speaker, doubling (approximately) the
    available power.

    You can't conveniently convert an amplifer to bridging if it wasn't
    designed that way. You really need to check with McIntosh, or at least
    in a newsgroup where people know all the details of these models (and
    someone will surely have a manual). rec.audio.pro usually deals with
    things other than high grade consumer amplifiers.
     
    Mike Rivers, May 1, 2006
    #3
  4. Adam

    Adam Guest

    Sorry guys, you are right. I will call McIntosh and get a manual from
    them.


    Best regards, and sorry for the spam,

    Adam
     
    Adam, May 1, 2006
    #4
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