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MC240's & Martin Logans

bre's dad

bre's dad

I drank what?!?
Martin Logan & McIntosh question. I'm looking at getting a set of ML Aerius i (as long as the panels are good). I'm wanting to drive them with a pair of McIntosh MC240's bridged mono. Would this be sufficient or too much of a load on the amps? I'm not worried about the power aspect as much as I am the impedance as I've read these can drop below 2 ohms.
 
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According to their website "Impedance 4 Ohms, 1.7 at 20kHz Compatible with 4, 6, or 8 Ohm rated amplifiers". Could be problematic.
 
The answer is yes, the MC240 is rated for 2Ohms in mono mode.

One difference between "bridged" and parallel is that bridged doubles the voltage (gain) by inverting one channel and stacking them without any additional current capacity, parallel doubles the current by load-sharing and the voltage (gain) remains the same. Bridged is not going to help with a difficult load.

Both can be shown as doubling the power output (watts) available.

In the case of the MLs or other difficult loads, you would want parallel, which fortunately is what the MC240's MONO mode delivers. Whether that will sound good to you is another question.

With the transformer output, and adequate current capacity within the impedance range, you should be able to achieve a constant / level amplification into the load. IF the MLs respond to this well, you have a good match.

Many people like solid-state direct output for this application, because the power output is NOT linear, it increases as the impedance drops. What this does is to maintain the voltage (gain) as the impedance drops but pass as much current (within limits) as necessary to maintain this gain. Speaker excursion is like a voltmeter, the larger the voltage the further the cone (or diaphragm) moves. If the current is maintained then it will do a better job of maintaining the relationship between driver movement and signal. There is also the (often overblown) talk about damping factor, which is irrelevant once you get to a fairly low number, yet people who can't separate theory from home audio will tell you that you need a damping factor that is much higher than the speaker and wires actually have, ... another discussion.

So the answer is that yes, the MC240 in parallel (MONO) is capable and rated for a 2 Ohm speaker (on the 4 Ohm taps). Whether the Martin Logan speakers are designed to require the current-spike capabiliy of direct-coupled SS or the consistent impedance of output transformers is the more important part, and will likely only come from those who have tried the pairing.

If you already have the amp, and plan to buy the speakers I say try it and you might love the pairing. If not, well you already had the amps and they're pretty easy to sell.
 
The maximum capability of a pair of MC240 in mono parallel will be 100 wpc when connected for 2 ohm operation but will be less when the amplifiers see 4 ohms from the speakers. A single MC2255/2250 or MC7200 or MC7300 would be far better suited for the task while being significantly less expensive than a pair of MC240s in good condition, to say nothing of higher expected cost- both in dollars as well as the hassle. I like vintage tube equipment as much as anyone but this route is simply impractical, IMHO.
 
62caddy said:
The maximum capability of a pair of MC240 in mono parallel will be 100 wpc when connected for 2 ohm operation but will be less when the amplifiers see 4 ohms from the speakers. A single MC2255/2250 or MC7200 or MC7300 would be far better suited for the task while being significantly less expensive than a pair of MC240s in good condition, to say nothing of higher expected cost- both in dollars as well as the hassle. I like vintage tube equipment as much as anyone but this route is simply impractical, IMHO.
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I already have the 240's, just wondering how they would pair up with the Logans. I also have a 2105 that seems to be better suited, if I get the Logans. The seller has to come down as they would need replacement panels probably in the near future. Realistically, this may not even happen.
 
I had the original version of the Aerius speakers. I ran them on a sub 10 watt tube amp and enjoyed the result. No head banging with this setup however. It was a zero feedback class A PP amp if that makes any difference. I say try it.
Good luck,
John
 
The Aerius i's didn't happen, bad panels in both seakers. Guy wouldn't come down much off his asking price which was borderline too high to begin with. Doesn't make any sense to spend about a grand on bad speakers and then dump another grand into new panels, with a 4 month wait on them (contacted ML support before I went to look at them.) There is a set of Quest Z's I auditioned a couple of weeks ago I might go back for. They're pretty damn big though.
 
Not sure about bridged MC240s, but when I tried to get more power out of a pair of MC225s, I did indeed get more power, but much of the MC225 magic was gone..
 
Jeff you better read a MC 240's owners manual. You can wire the outputs in series or in parallel using the mono input. So thats two to thirty two ohms. Plus there is a 600 ohm output and a 70.7 volt output in stereo. and I believe in different variations in mono. Same goes for series one 275's with the octal output socket. You can even wire the 4 ohms in series to drive a center channel summing the L + R while using using the 8 0hm taps to drive the Left and right speakers in stereo. I have seen it done and done the same driving three Cornwalls for a Klipsch three channel system. If you reverse the polarity on one channel with your stereo pre-amp and then reverse the polarity on that same channel speaker output then you have L-R for the ambient signal for the center channel which Davie Obrien preferred and keep the main speakers in phase with each other. You can't do that with amps where the common is tied to ground.
 
I was unaware of that @twiiii thank you for the correction. I know it has a mono position on the switch and was only aware of the parallel connection option, guess I should blow the dust off of my manual before posting.
 
To my recollection, the idea of bridging amplifiers didn't really become a commonplace concept until chip amplifiers became a reality. With them in that mode, it became an economical way for two chip amplifiers to quadruple power output particularly in low supply voltage applications like automotive designs.

But back in the day of the MC240's original popularity, the idea of connecting amplifiers together for more power centered virtually exclusively on parallel operation for a doubling of power output. Therefore it's hardly surprising that there's no mention of bridging the channels for greater versatility/power output in the owner's manual.

I think it was only later when knowledgeable folks who understood the newly spotlighted concept of bridging amplifiers as well as the Mac design, put two and two together to realize that bridged operation was possible with the un-grounded output windings that Mac employed. Once that happened, then it started to become common knowledge. But this was well after the last 240's owner's manual ever saw a printing press.

Dave
 
Oh, and to further confuse the issue, it was manufacturers like Bogen in the 60s who regularly referred to "bridging" many of their popular PA amplifiers, when really what they were describing was parallel operation of two or more units.

Dave
 
I run a pair of MC240's in mono into ML Electro Motion ESL's @ 4ohm. Never lacking in power or volume. In fact, they sound amazing driven that way.
 
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