McIntosh MC 275 Commemorative power amplifier Page 2
But a funny thing happened on the way to the bank. The MC 275 sold out fast. When the limited edition was over—identified by the plaque—a non-limited edition followed. McIntosh began to take tubes seriously. Again.
Was the MC 275 Commemorative a real MC 275? It was made in the same factory with the same tooling and it used the same circuit, etc. Point-to-point wiring was replaced by three circuit boards. The transformers were, more or less, the same as those used in the original MC 275. à la carte, the original MC 275 was last seen selling for $4000 plus $500 for the tubes. The new MC 275 sells for $3500, prix fixe.
Unlike the revived MC 275, the new MC 2000 and MC 2102 were totally new amplifiers with current McIntosh styling: backlit faceplates and blue meters. They were more powerful than the MC 275, using four KT88 output tubes per channel rather than two (6550s could be substituted). And they incorporated new things that McIntosh had learned over the years from making solid-state amps.
Still, there was this link to the past. All these tube amplifiers employed the McIntosh "unity-coupled circuit," which was covered by no fewer than "six US government issued patents," according to McIntosh back in the 1960s. The patents expired long ago, but McIntosh continues to have a lock on the circuit—because, in order to implement it, you must wind your output transformers in a certain way. McIntosh has that capability.
Tubes deliver power from a high output impedance. To lower that impedance—so that tubes can drive loudspeakers—you need an output transformer for each channel. (Yes, I know there are output-transformerless (OTL) amps, but they're a special case.) Such transformers are heavy and costly, giving tube amplifiers a price disadvantage vs solid-state. Moreover, the wiring of output transformers is something of an art that is shrouded in mystery. Watch an output transformer being wound and you'll know what I mean.
In order to implement Frank McIntosh's circuit, you have to wind the transformers the way they do in Binghamton. Not the usual two, but three transformer windings are needed: two primaries (one for the plates, another for the cathodes) and a secondary. The two primaries are spun bifilar—the two strands are wound together tightly for a close, turn-by-turn coupling. This is where the "unity-coupled output circuit" gets its name. The cathode winding provides near-instantaneous local feedback. This feedback is said to reduce distortion, especially at the frequency extremes—ie, top and bottom—leading to tight bass and open treble.
Heh-heh. "Feedback correctly applied," stated Larry Fish, McIntosh's vice president (retired) of product development.
Most tube amps draw power only from the plates of the output tubes. Frank McIntosh had a different idea. In the McIntosh circuit, half the power is taken from the plates and half from the cathodes, so that power is drawn from both sides of each output tube. More bang for the buck, as it were. Frank McIntosh was of Scottish ancestry, after all. Thrift!
Maybe more reliability, too. Mac tube amps have always been notoriously reliable. McIntosh makes no claim to this effect, but I've discussed the matter with Mac people from time to time. The McIntosh circuit, in its symmetry, may be easier on output tubes than conventional circuits.
The main advantage, according to McIntosh, is that you get high power with low distortion.
Meanwhile, now that they were taking tubes seriously again, Sidney Corderman and McIntosh continued to learn new things about them. Tube chimneys—little cups around the sockets of the output tubes designed to cool the tubes naturally by convection—are a Corderman innovation. These were introduced in the MC 2000 and MC 2102, and the latest MC 275 has them as well. I can't understand why other manufacturers haven't adopted this. [The idea is catching on. Hovland's Sapphire, reviewed by Michael Fremer in March 2002, had chimneys around its output tubes, as does the T+A V10 reviewed by Mikey in May 2004.—Ed.]
There were other changes for the new MC 275. Three circuit boards have been reduced to a single board on which all components, tube sockets, and power-supply parts are mounted.
Ron Cornelius: "Some people feel that the best design is a traditional point-to-point wiring, as we used in the original MC 275. But a properly designed single board yields a superior signal/noise ratio and eliminates a lot of wires which act as little antennas.
"The new design uses ceramic tube sockets with gold-plated pins. The new MC 275 also uses DC 12V for the input tube heaters, which improves signal/noise ratio. The original MC 175 was rated at 90dB S/N ratio. Modern custom poly-caps allow greater than 100dB S/N ratio."
The new MC 275 features a removable power cord. There is now an On/Off power switch, even if it's awkwardly located (nothing Mac could have done about that). Speaker connections are by a power strip, with taps for 4, 8, or 16 ohms. You may have to re-terminate your speaker cables accordingly.
The trannies have been beefed up—both the single power transformer and the two outputs. They're much bigger than before—so big, according to Ron, that they can scarcely fit inside the transformer cans. Yet the look of the original MC 275 has been preserved. The chassis is of easily maintained stainless steel. All tube sockets are now ceramic. When you use the balanced inputs, as I did for most of my listening, the gain-level controls don't operate.
Gosh, Sam, enough with this dancing around. How did it sound?
I ran the McIntosh MDA 1000 D/A converter straight into the MC 275, using the converter's gain control. Speakers were the Opera Callas and Quad ESL-988.
I heard all the dynamic quality, all that aliveness of the original—and the original revival—plus a level of transparency that brings the MC 275 definitively into the 21st century. I heard timbral accuracy. Delicacy. Definition. The amp performed as McIntosh claimed it does: It got out of the way. And it let me hear what the MDA 1000 was capable of. A brand-new 21st-century DAC into an amp that goes back more than 50 years, if you count from the development of the McIntosh circuit.
The MC 2000 was a limited edition, a onetime event to celebrate McIntosh's 50th anniversary. The MC 2102 continues in production, with more power than the latest MC 275; and, as I said, it matches the current styling of other McIntosh products. I'm not sure which is the better-sounding amp, the MC 2102 or this latest MC 275. I've gone back and forth. The MC 2102 is more powerful, and sounds it, too. It produces the sound of a big tube amp—dynamic, dimensional, holographic.
Yet this new version of the MC 275 just does something. To my ears, it rivals the sound of single-ended triodes. It's intimate, insightful, and alive. It has a SET-like touch with transients—so clearly and cleanly articulated, with no smearing at all.
What's more, for a tube amp, the top and bottom registers are handled particularly well. The treble doesn't seem rolled-off. The bass is firm and authoritative—punchy, if you will. But, yes, the MC 275 can run out of steam during difficult, dynamic passages compared to the MC 2102.
Ron Cornelius tells me that the MC 275's rating is still 75Wpc, although this latest version is said to kick out closer to 100Wpc. The output tubes are Russian, from Seratov or St. Petersburg, and checked out in Binghamton. You can substitute 6550 output tubes for KT88s, but you can't mix and match.
Maybe you won't want to buy a "new" McIntosh MC 275. Nonetheless, do take a look and give a listen. For the price, it's at least as good as anything else I've heard, and the nostalgia is thrown in as a bonus. It's McIntosh's lowest-priced (and lowest-powered) stereo amp. It's up there with their very best current products, both tubed and solid-state. And if you need more power, you can bridge two of them into mono by flipping a switch.
In other words, the MC 275 ain't no antique.
I snagged serial number 2.