McIntosh Labs MC75 Mono Amplifiers
by Mark Blackmore | March 7, 2017
© www.theaudiobeat.comWhen I learned I'd be reviewing the McIntosh MC75 monoblocks, my first thoughts were, What's a fanboy of single-ended triode amps need with 75 watts of push-pull power? My speakers don't need all that! My last amplifier purchase was a beautiful Yamamoto A-08 that uses two vintage 45 output tubes to produce a whopping 2 watts on a good day. Yet, there I was, staring at another beautiful amp with retro styling, polished stainless-steel deck -- and enough power to get me into trouble quickly. For the last decade I've traveled down the low-watt/high-sensitivity road, listening to triodes with an occasional dabble into low-powered class-D chip amps, so the McIntosh MC75s would be something entirely different. Would they entice me to veer off the SET path?
The MC75 was originally sold from 1961 to 1970, and that amp is a very close cousin to the new version under review. Input tubes have changed slightly over the years and modern speaker binding posts have replaced the terminal strips of the original. This new amp uses a 12AX7 as a phase splitter, then two 12AT7s as the driver tubes for the pair of KT88s, with all of the tubes branded "McIntosh." If you feel the need to try different tubes with the MC75, there are a number of new alternatives available as well as any number of new-old-stock choices. I didn't swap any tubes during the review as I felt the average owner would keep everything stock, but there are an awful lot of possibilities and prices are reasonable, so have fun.
Measuring 16.5" x 8.5" x 8.5" and weighing 38 pounds, the MC75 is awkwardly heavy due to all of the weight in the power and output transformers on one side of the frame. For a basic mono power amp, the MC75 has quite a few features to discuss. Power is rated at 75 watts into 2-,4- or 8-ohm loads with less than 0.5% distortion and, although it's not listed, Mark Christensen of McIntosh confirmed that the output impedance is less than 0.5 ohm, which is almost in solid-state territory. We'll return to this later.
McIntosh's patented Unity Coupled Circuitry is used for improved power-supply efficiency and cooler tube temperatures. The MC75 certainly is the coolest-running tube power amp I've ever used; the tube cages were merely warm, not hot, after an entire afternoon of listening. My CD player gets warmer than the MC75. And in case something would go wrong, the MC75 is protected by the Sentry Monitor Tube Protection Circuit, which protects the amp if there is a short in the speaker wires or an output tube fails. The MC75 can be powered on by an accompanying McIntosh preamp using the Power Control Connector. Single-ended and balanced inputs are available and are selected by a small switch on the faceplate, and McIntosh has included a second set of XLR and RCA jacks labeled "In/Out" for feeding another amplifier if you want to daisy-chain amps in an elaborate system.
Between the input terminals is another switch that sets the input sensitivity to either 1.7v or 0.85v to better match the amp to a variety of preamp choices. It dawned on me that this meant one could try using a passive preamp or DAC with variable outputs with the MC75, and I wish more amps came with this feature. I used both balanced and unbalanced inputs during my audition and neither seemed to have a sonic advantage in my system.
Unpacking and setup were a breeze. Once the amps are out of their boxes, the owner must remove a pink foam insert from the tube cage that protects the tubes during shipment. McIntosh covers the tube cage with a warning label so there can't be any mishaps. This is the first time I've gotten an amp with the power tubes already in place, so if you are new to tubes, this is one tube amp that will be easy to install and use.
How does the MC75 differ from its more famous sister, the stereo MC275? Each amp is rated at 75 watts per channel and they share the same power supply. The difference is that the stereo MC275 has to power twice as many tubes in its chassis, and that power supply has to support the MC275's ability to become a monoblock with twice the power. So a pair of MC75s basically has twice the power supply of a single MC275. This translates into an overbuilt, cool-running power supply for each MC75. Another difference is how McIntosh handles balanced inputs: a 12AX7 tube for the MC275, but, due to space issues, McIntosh opted for an op-amp for the MC75. A benefit of this change is that the S/N is improved by 5dB, to 110dB, for the MC75.
From a cosmetic point of view, which is no small consideration when you're talking about McIntosh electronics, I prefer the MC75, for a few reasons. First, building on a mono chassis gave McIntosh the room to place input and output plugs side by side instead of the over-and-under arrangement of the MC275. Wire runs were neat and tidy, and I liked the short gold-plated five-way binding posts instead of the large hexagonal posts used on the stereo version. Finally, while I think the MC275 is a good-looking amp, I greatly preferred the MC75's understated natural tube glow instead of the added green LEDs under the MC275's input tubes. Feel free to disagree, but to my eyes the MC75 is the classier-looking amp.
I began my listening with the MC75s connected to a pair of Altec Valencias that are on long-term loan from a local audio buddy. As expected, the very efficient Valencias proved to be no challenge for the MC75s, and they appreciated the extra power on tap. There was a definite break-in period for the amps of at least 100 hours. At first listen, the treble was attenuated, closed in and hooded. Changes to interconnects and speaker cables didn't change the sound much, so I just let the amps settle in for the first couple of weeks. After break-in, I did swap the supplied power cords for a pair of Shunyata Zi-Tron Sigmas, and there was slightly improved lower treble, so I left them in the system for the rest of the listening period. Once broken in, the MC75s usually needed between 15 and 30 minutes of warm-up time to sound their best, so consider that if you are in a store for an audition.
The MC75s displayed an obvious sense of ease driving the efficient Valencias. It isn't revelatory to say that the Altecs could play louder with more power, but the MC75s struck me as more powerful than their rating would suggest, and that power came without edge or grit. Percussion and sudden fortes brought the "jump factor" that J. Gordon Holt described many years ago. Since it was the holiday season, I spun Tchaikovsky's The Nutcracker by the Kirov Orchestra and Valery Gergiev [Philips 289 462 114-2]. I had the volume at a healthy level, but in "The Nutcracker battles against the Army of the Mouse King" there is a gunshot that scared me and my wife and caused both cats to jump off our laps. We laughed, but I also turned it down a bit. The MC75s could play loudly with so little strain that I learned to be careful with the volume knob.
That power also brought an extra octave of bass response. Well, not really, but the MC75s did give bass notes adequate power to energize the room. "Lunar Tides" and "Higher Calling" from Glen Velez's Breathing Rhythms [SoundsTrue 1-56455-821-5] are favorite tracks of mine. The low thrum of the pandero was more powerful, and that extra power revealed some lower notes that had only been suggested with my usual low-powered SET amps. The MC75s gave the 16" woofers enough juice to make the living room jump, and notes that had gone unnoticed now became part of the rhythmic structure. Bass was full and more round than with an equivalent solid-state amplifier, but not fluffy or loose. Timpani were particularly energetic, and I recommend Hans Vonk leading the St. Louis Symphony playing Beethoven's Symphonies Nos. 5 and 7 [Arch Media AM-1004] to hear how their timpanist, the late Richard Holmes, could deliver both power and perfect timing to propel the music.
Another consistent trait that the MC75s demonstrated, regardless of which speaker I used, was superb soundstage depth. I first noticed this on Jacques Loussier Trio's The Four Seasons CD [Telarc CD-83417]. During the opening track, there are some fun studio effects at the 1:15 mark. Vincent Charbonnier's bass lick is repeated four times: close and dry, then far away with some reverb, then at medium depth and dry, and finally way back surrounded by lots of reverb. The MC75s did a great job with that huge dome of reverb, so I went to look for something with natural recorded depth instead of this studio synthesized variety. I found it in José Cura's wonderful album of Argentinian songs Anhelo [Erato 3984 23138 2]. It was recorded in the Orchestra d'Ile de France, and there is a real sense that you are seated in the first few rows of the hall with a perfect balance between direct and reflected sound. I dislike cavernous recordings that highlight the size of the venue but rob the listener of the emotion and technique of the performers. "Canción del árbol del olvido" by Alberto Ginastera presents Ernesto Bitetti on guitar and Cura's voice at my preferred distance for the vocal line. The MC75s kept his voice centered in the soundstage with a good blend of direct and reverberated sound in that large concert hall. Thankfully, the MC75s did not add body or warmth to his voice, as some more tubey-sounding amps might.
Another choice to show off the MC75s' depth would be one of the many titles from MA Recordings using only two omnidirectional microphones. My first choice has been The Lute Music of Johann Sebastian Bach Vol. 2 [MA Recordings MO54A]. Eduardo Egüez plays in a highly reverberant space and his sound can get lost in the acoustics. The MC75s certainly emphasized the reverberation and came close to swamping the direct sound, but they still managed to portray his lute with good tonality and appropriate size.
If depth was a definite strength of the MC75s, width was merely good. I found this strange because past experience led me to believe that switching from a stereo amp to monoblocks always slightly enhanced width. But the MC75s kept images squarely inside the speakers, with only an occasional studio effect venturing outside the speaker cabinets. I don't consider this much of a disappointment and just moved my speakers a bit wider than normal to compensate for the narrower soundstage. Center images stayed locked into place, and I was able to get a larger and wider soundstage, so I would encourage you to try the same when auditioning the Macs.
I knew I needed to try some speakers that were a little more challenging than the easy-to-drive Altecs. I'd heard that McIntosh tube amps loved electrostats, so I moved my pair of InnerSound Eros speakers into the living room. The Eros is biamp only, so I let the MC75s tackle the electrostatic panels, which play only above 300Hz. They are relatively efficient but pose a challenging impedance curve starting over 120 ohms at the crossover point and heading down to a bit under 2 ohms at 20kHz. This punishing low impedance has been known to cause an amp or to emit awful buzzing sounds. Since the Eros uses a pro-audio electronic crossover, I was able to try the MC75s' balanced inputs, and the sensitivity switch came in handy in achieving a good level match between the MC75s and the InnerSound solid-state amp used for bass duties.
The MC75s had absolutely no problems driving the electrostatic panels to full volume with extended treble response. Triangles and cymbals were clear and had long reverb tails when the recording allowed. Due to the MC75s' low output impedance, they will be less likely to roll off the extreme treble as the electrostat panel's impedance dives towards zero. This speaker proved to be the best partner with the MC75s, and I spent many days listening to old favorite jazz combos and classical music. Instrumental and vocal lines had good clarity without added warmth, coupled with a deep soundstage. The Eros is very precise in portraying the soundstage, and the MC75s made it easy to "see" individual performers on the stage. A non-audiophile friend stopped in for a listen and said, "Wow, those are really good speakers," but I added that I believed the MC75s' control and extended treble had a lot to do with the fine sounds we were hearing.
Did the MC75s tempt me to abandon SET amps? Not really. I'm too far down that road and too old to start over, but that doesn't mean these amps couldn't be a wise choice for you. They are powerful, quiet and flexible, and they should mate well with a wide range of speakers, as my experience with the InnerSound electrostats indicated. They run cool enough to use all summer long, and I would imagine that the KT88 output tubes will last a long, long time before needing replacement. Just be sure to have your McIntosh dealer give the amps a good, long warm-up so you hear them at their very best.
Price: $7500 per pair.
Warranty: Three years parts and labor.
McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, NY 13903-2699
Associated EquipmentAnalog: J.A. Michell Gyrodec turntable with Orbe platter and bearing; Ortofon TA110 tonearm and cable; Sumiko Blackbird, Denon DL-103R and Yamamoto YC-03S cartridges; Fosgate Signature phono stage.
Digital: Consonance Droplet 5.0 CD player, Korg DS-DAC-100 digital-to-analog converter.
Preamps: McCormack TLC-1, Yamamoto Soundcraft CA-04.
Amplifiers: InnerSound ESL, Yamamoto Soundcraft A-08 and A-09.
Speakers: Altec Lansing Valencia, InnerSound Eros.
Cables: BPT IC-SL and MIT Shotgun S1 interconnects; BPT SC-9L and InnerSound ESL speaker cables; BPT C-9 and L-9CST, Yamamoto (came with amps) and Shunyata Research Zi-Tron Sigma power cords.
Power distribution: BPT 2.0 and CPT.