Dual Mono with Older Amplifiers

Discussion in 'McIntosh Audio' started by welcomdmat, Sep 5, 2017.

  1. welcomdmat

    welcomdmat AK Subscriber Subscriber

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    I apologize if this should be in another area, but my thoughts have been to run dual mono with McIntosh MC2100s.

    When amps are as old as the 2100, is there/ what needs to be done to make sure the two amps are running a similar output?

    I think that makes sense -- if my amps are both from the mid 70s -- and each one is in charge of one channel -- how do I make sure that everything is equal?
     
  2. damacman

    damacman Blown and Injected Subscriber

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    Best to begin by thoroughly cleaning the Stereo/Mono switch. It's also helpful if both amps have been recently serviced and meet spec.

    To ensure equal output from each amp, just:
    - disconnect loudspeakers
    - turn Right gain controls on both amps to MAX
    - play 1kHz test tone recorded at 0dB off of a CD and increase volume on preamp to 11:00 or so
    - use DMM to measure output at each amplifier, one will be lower
    - reduce gain setting on the amp that reads higher to match voltage at the one that reads lower

    I'll typically compare results at a few different volume settings to rule out channel imbalances on the preamp. Once you're happy with the results of your efforts, reconnect the speakers and enjoy.
     
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  3. twiiii

    twiiii Super Member

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    But make sure the out put of your preamp is equal to both channels first. I would use one channel and a wye cable to drive both amps. Set the right control to the 12 : 00 position on the power amps in the mono mode and advance the volume to 2 volts of one amp, then check the other it should be very close if not identical to the first.
     
  4. jdcarlson

    jdcarlson Not Good Enough for Jazz Subscriber

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    Put a MEN220 between the MX113 and the MC2100s. By the time you go through the room knowledge procedure with the MEN220, it will solve ANY out of balance problems between channels, whether pre-amp, connectors, amp, speaker wires, or speakers.
    At my office, I have a MX118 feeding a MEN220 feeding four MC2255s (similar vintage as your gear) bi-amping Legacy Signature IIIs. Works like a charm.
    To me the MEN220 was the best investment I have made in my audio system.
    Thanks,
    Jim
     
  5. techguy0192

    techguy0192 AK Subscriber Subscriber

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    Here's a good question. Why do you need a pair of 2100s? Is your room that large and/or speakers that hard to drive? A 2100 in good working order should be capable of well over the rated 105 watts per channel.
     
  6. welcomdmat

    welcomdmat AK Subscriber Subscriber

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    Boredom. I may never do it, but I have been told my MC2100 is late production. It has seen modest work (caps replaced as needed versus some that have been overhauled).

    I have kept my eyes open for a virtually new example. Something that was an estate sale example of one nearly perfect. At first I envisioned selling the lesser of the two, but the idea of running both on stands near my speakers came about due to some of the amazing pictures available here.

    My question is as much about MC2100s as MC50s if they are not purchased together.

    I honestly couldn't live without loudness control based on my listening area. My speakers are 95db sensitivity . . .
     
  7. MurrayLives

    MurrayLives AK Subscriber Subscriber

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    Symmetry?
     
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  8. jdcarlson

    jdcarlson Not Good Enough for Jazz Subscriber

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    It is called "headroom." I have four MC2255s driving speakers in 250 sq feet. At one time I had a single MC7270 doing the same thing. The mono mode on the amps, with active crossover and bi-amping, just gives the sound a little more authority. You do not feel like the amp is going to run out of power.
    Also, you are running the amps at less than half their rated power - perhaps 1/10th of their rated power (my MC2255s - rated 250 WPC - or 500 watts in mono mode - rarely get above 0.25 on the meter - which would be 0.5 per channel - when they get to 2.5 on the meter - which would be 5 WPC - my son makes me turn the sound down).
    Also, you know you are "working" in the lowest distortion range the amp has.
    Thanks,
    Jim
     
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  9. cduarte

    cduarte AK Subscriber Subscriber

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    this is exactly why I use my mc2300 to drive my Cornwalls in the summer, it's not quite as sweet as the mc30s or mc225, but transients and cymbal crashes and of course bass is truly impressive, not that they're ever bad with the mc225 or mc30s or even the pair of mc225s run in mono. I'd like to try an active crossover myself and use the mc2300 to drive the woofers and the pair of mc225s to drive the horns individually. I think once dialed in, it would be an amazing setup.
     
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  10. motorstereo

    motorstereo the wonder of it all Subscriber

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    The main reason for me is a pair of 2100's just plain sounds better than a single 2100 on every pair of speakers I've ever used them on. It could be increased headroom or better channel separation or it could be the sound changes on them when they're strapped or it could be the pre-amp is a better match for them when there's 2 of them.
     
  11. techguy0192

    techguy0192 AK Subscriber Subscriber

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    I fully understand headroom. The question was more of a way to possible prevent him from wasting money. If he has really efficient speakers, a small room, or maybe a combination of both, there's not much need for a pair of 2100s running bridged. Having owned several McIntosh amps with meters, I know what a single watt of power is capable of. Personally, I've never had one read higher than 5 watts. Program material and listening habits do have an impact. Yes, I think a pair of 2100s would look cool. It's up to the OP to decide if the extra money is worth what he might gain. In my experience, I would rather have a more powerful stereo amp than use two smaller stereo amps bridged to get the same amount of power.
     
  12. welcomdmat

    welcomdmat AK Subscriber Subscriber

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    Even if my question is completely academic, we have gotten away from it.

    If one MC2100 was built in 1969 and the other in 1975, how can the 2017 user of modest electronic knowledge use these for a two amplifier mono setup? 105 watts into stereo is the list, but these amps were built 6 years apart 40/ 45 years ago.

    They both look good. I understand that late MC2100s had large capacitors in blue instead of silver (I'm told they are original). I have one that is blue and one that is silver. I want to run some Pioneer CS-99a speakers in a 18'x24' space

    Purely academic, of course
     

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    Last edited: Sep 11, 2017
  13. techguy0192

    techguy0192 AK Subscriber Subscriber

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    Consider taking both amps to a tech to have them bench tested, and matched.
     
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