McIntosh Laboratory MC462 power amplifier

It hit me not long ago: I need more Mac in my life! I promptly purchased the current production version of McIntosh Laboratory's time-honored MC275 tubed amplifier, to mate to the Mac C2300 tubed preamplifier I already owned. The recently reinvigorated debate in these pages comparing solid-state and single-ended tube designs got me to thinking. One thing led to another, and voilà! McIntosh's latest solid-state stereo amplifier, the MC462 Quad Balanced ($9000), arrived, bolted to a shipping pallet and encased in two big, heavy, nested boxes. All that packaging weighs 33 lb—the amp inside weighs 115 lb. If you want to lift it onto a rack, you'll need two people, a serious handcart, and a strong, deep shelf.

Frank McIntosh and his company got off to a very strong start in 1949, in Silver Spring, Maryland, with their first product, the tubed Unity Coupled 50W1 Power Amplifier. A patent was granted that same year for the Unity Coupled circuit and transformer. In 1951, McIntosh Laboratory moved to Binghamton, New York, where they've been ever since.

A week after the MC462's arrival I saw for myself, on a guided tour of the plant, how it all comes together.1 I could feel McIntosh's conservative approach: doing the maximum, not the minimum, at all stages of design and manufacturing, to maintain a high level of quality.

What are you?
The solid-state MC462 power amplifier replaces the MC452 and is now the most powerful stereo amplifier McIntosh offers, with a specified continuous power output of 450Wpc into 2, 4, or 8 ohms, and peak output current of 75 amperes per channel. (McIntosh claims a 66% increase in dynamic headroom over the MC452, achieved by a big increase in power-supply filter capacitance.) The MC462's distortion is specified as not exceeding 0.005% at rated power output, and as no more than 0.002% in the mid-frequencies.

In the MC462, which operates in class-AB, the concept of complementary pairs is taken to an extreme. In most push-pull amps, the two phases of the signal waveform are amplified separately by two single-ended amplifiers, the outputs of which are then combined to recreate the waveform in full—and in the combining, some distortion products are cancelled out. What McIntosh has created is a push-pull amp in which each phase of the signal waveform is itself amplified by a push-pull output section: There are two complete push-pull amplifiers in each channel, their outputs combined in what McIntosh refers to as a Quad Balanced architecture.

The design element that allows McIntosh to do this has been a technical cornerstone of all their solid-state amps: a single-winding transformer called an autotransformer—or, in the trade lingo arguably coined by McIntosh, an Autoformer. Beginning in 1967 with their first transistor amp, the MC2505, McIntosh has used output-stage Autoformers to optimize impedance matching between output devices and loudspeaker loads, as well as to protect the latter from DC. Fifty-two years later, an output-stage Autoformer allows the company to combine the outputs of multiple push-pull amps in a manner that, they say, has unprecedented distortion-cancelling capabilities. (This is also how the MC462 can deliver the same 450Wpc output to its pairs of 2, 4, or 8 ohm speaker taps.)

All of this firepower ran amazingly cool—when I laid a hand on the top panel, it was barely warm. This cool running is in part achieved through what McIntosh describes as their current-generation ThermalTrak Power Transistors; the MC462's power output circuit monitors their temperature and adjusts bias accordingly. Another reason is the extensive, heavy-duty heatsinking built into the rear half of the MC462. These include a nice touch: the initials MC are formed by the sinks' vertical fins and are visible from above—as if you're standing atop a subway grille on a Manhattan street. Also visible from that vantage is evidence of McIntosh's pride in the MC462's lineage: circuit block diagrams handsomely adorn the top plate.


At 17.5" wide by 9.45" high by 22.5" deep, the MC462 occupies an impressive amount of real estate, but finding room for it wasn't as hard as I at first thought—that 22.5" depth includes the two hefty handles on the faceplate and the rear deck on which the speaker terminals are vertically arrayed, and the amp's four rubber feet are sensibly separated by only 12.5" from front to back. The black glass faceplate proudly displays two large meters backlit in McIntosh blue, each about 5.5" wide by 2.5" high. The meters' upper scale is calibrated in watts, to indicate the MC462's output: the large numbers top out at 450, and after that, in smaller numbers, come "900" and "1.8k," referring to the amp's dynamic headroom: brief bursts of wattage beyond the MC462's rated continuous output. The MC462's specified dynamic headroom is 3dB—in the real world, that's a lot. The meters' lower row of figures calibrates the amp's output in decibels, from –50 to 0.

The rest of the front panel is minimalist. There are a green-lit "Olde English" McIntosh logo and three small red LEDs: one indicates Standby status, and the other two tell you when the Power Guard circuit kicks in. There are only two control knobs: the one at left, labeled Meter, turns the meters' Lights Off if desired; the Watts setting shows you real-time meter readings, while Hold lets the needles linger on peak output levels before slowly resuming action. The other knob, Power, has positions for Off, On, and Remote, the last for connecting to a McIntosh preamp for power-up/down sequencing.

The rear end of the MC462 is straightforward. In addition to the six pairs of speaker output taps sticking straight up from the shallow rear deck are AC in, a fuse bay, and, jutting out horizontally from the rear panel, pairs of balanced and unbalanced inputs and outputs. One small switch lets you select between balanced and unbalanced operation, and with another you can enable or disable the Auto Off function, which shuts down the MC462 after it hasn't sensed an input signal for 30 minutes. I particularly liked McIntosh's patented gold-plated speaker binding posts. Each has two moving parts, which you first tighten with your fingers, then tighten a further quarter-turn with a small wrench (supplied), for a snug connection.

System and setup
Not wanting to face too many variables, and to give the MC462 enough time to break in, I spent my first days with my system unchanged, listening to my Harbeth 30.2 40th Anniversary Edition loudspeakers, which Herb Reichert reviewed in April 2018. Central upstate New York, where I live, benefits from ample clean power, but kicking that power's quality up a big notch is my AudioQuest Niagara 7000 power-line conditioner.


What first caught my ear when I cranked up the MC462 was nothing—no noise of any kind through the speakers or directly from the amp itself. Control of mechanical and circuit noise seems to be a real strength of McIntosh products—I'd had a similar experience when introducing the McIntosh MC275 amp into my rig. The two amplifiers in my reference system that had preceded the MC275, a solid-state and a single-ended tube design, each produced some level of hum, as well as noise through my speakers, that I could never eliminate. But the MC462 provided those impressive backgrounds of "black" silence deeply desired by audiophiles—they really do play a role in the appreciation of microscopic and macroscopic differences in levels of detail and dynamics of recorded music.

The music goes 'round and 'round . . .
We all have our default settings. Each February, for Stereophile's annual "Records to Die For" feature, I could happily pick Shirley Horn's Here's to Life (CD, Verve 314 511 879-2). Every time, it's the first recording I reach for when I want to hear wussup in my system.

I cued up "Return to Paradise." Hearing music from the MC462 for the first time, I thought of visual metaphors. I thought of turning the contrast setting up or down on a television, or adjusting the amount of color saturation. Zooming in and out also has its audio analogs. The audio picture—the soundstage width and depth—enlarged in all parameters, and the colors seemed deeper. I heard a kind of fleshing out of Horn's voice, her deep mezzo gaining heft and impact. The other aspect that grabbed me was the percussion in this track, which is complex and subtle, capable of revealing a system's ability to resolve minute details. I heard intricate percussion sounds that I didn't recall having heard before, and the drum kit also had more impact, with more swing.

McIntosh Laboratory, Inc.
2 Chambers Street
Binghamton, NY 13903
(607) 723-3512

Bogolu Haranath's picture

JA1 said it all ..... "It is an extraordinarily well engineered, exceptionally powerful amplifier" :-) ........

Ortofan's picture

... why do we need recordings with a resolution of any greater than about 18.5 bits?

Also, if the moral is to match the MC462's nominal output to the lowest impedance magnitude of the loudspeaker used, then which tap - 4 ohm or 2 ohm - is the better choice for a speaker that has a minimum impedance of 3 ohms, such as the B&W model used by the reviewer?
Depending upon which amplifier output tap is selected, there seems to be a trade-off between maximum power output and lowest distortion.

georgehifi's picture

Yet why review such an amp with these speakers that are easy loads, even a NAD3020 could drive them? Surely those that intend to buy this 50kg back breaker of an amp, are going to go for more substantial speaker than these?
This amp should have been reviewed with Wilson Alexia or similar to see if it perceived persona is more than just skin deep, and not a show pony.

Cheers George

PaulRS's picture

Correct me if I'm wrong, but a single-winding autoformer that McIntosh uses will not block DC. Only a transformer, such as used on most tube amplifiers will do that.

SNI's picture

@Paul IRS
You are right about that.
An autotransformer does not provide electrical isolation, as it is a single winding transformer.
Primary and secondare are connected both electrically and magnetically.
Double winding transformers are only connected magnetically.
Hence the DC isolation.
Anyways a two winding transformer is not very good at blocking DC, as the core can be saturated, and then build up heat.
Thus the primary task of a transformer is either step-up or step down or isolation, not a highpass filter
Generally the autotransformer is a step up or step down device only.
Historically the autotransformer came into HIFI because of lack of power. The Atotransformer coupled as a step-up transformer could increase the voltage swing on the secondary side. At that time most speakers were relatively high impedance, thus a higher spl was possible.
In modern times high voltage swings are no problem, as transistors have develloped, so no one uses transformers anylonger besides MacIntosh.
For what ever reason they still do, I don´t know.
No transformer is a linear component, they are pretty heavily inductive,
so using a transformer in the output, will introduce distortion of the signal.
Of course this can be reduced with NFB, but basically it is a workarround of a problem, that isn´t really there.

Alan Tomlinson's picture

"No transformer is a linear component, they are pretty heavily inductive,
so using a transformer in the output, will introduce distortion of the signal."

Well said. That said, there are a variety of distortion forms out there, and some of them are euphonic. No less an engineer than Rupert Neve has been using transformers in his recording consoles for a long time, and it's not because he didn't receive the memo about transformer-related distortion. In short, McIntosh probably has a fundamental sonic reason for favouring autoformers.


Alan Tomlinson

SNI's picture

@Alan Tomlinson
You might be right, that specific persons regard the distortion introduced by transformers as euphonic, and thus musical in some sense.
This point of view is not shared by everyone though.
I.e. if you look at very high end microphones like DPA (used for measurements by Stereophile, amongst many), Neuman, Shoeps etc. do have TL versions of their top performers. (TL = Transformer Less)
The TL versions are recommended over the transformercoupled ones, but the transformercoupled can be neccesary in studios with long and mixed cable runs.
In smaller set-ups with few mikes, the TL is recommended for its cleaner sound and better transparancy.
I´ve heard the difference, and there is no doubt, that the TL is the better choice in the purist cases.

But the choice of microphones and the choice of a lot of other recording gear, can be seen as a part of the musical expression.
An A/B stereo recording of Nirvana ore something, would probably not work in real life.
But IMO this kind of deliberate colouration should be held inside the recording studios. I don´t think it is wise to introduce stuff like that in the reproduction chain, as well as I cannot imagine that doing so will go well most of the time.
Good and sensible engineering with as few idiosyncratic elements as possible, will be best for the long haul I think.
Not that listening should be left out of devellopmentlabs, indeed not.
But the chances for good sound are present, but not in anyway garantied by good measurement results. On the other hand, I´ve not yet experienced good sound from equipment with bad measurements.
I don´t like distortion, no matter how euphonic it might be. It´s always there, and will be recognised as distortion eventually.

Best regards


jmsent's picture

No, an autoformer can't completely block dc. But when you consider the dc resistance of the autoformer winding, where the input tap is connected to the output transistors, and the other end of the winding is ground, you're probably looking at something on the order of a fraction of an Ohm. So, it's pretty likely that a dc fault condition would let very little voltage through to the speaker and pretty quickly blow an internal fuse in the amplifier. I believe that later Mac amps also have considerable additional fail safe circuitry in them that would disconnect the speakers in the event of any dc offset condition.

Bogolu Haranath's picture

There is information about transformer and auto(trans)former in Wikipedia :-) ..........

SpeakerScott's picture

The autoformer will present a very low impedance to DC. The older autoformers on McIntosh amplifiers are approximately .5H winding inductance (more on that in a bit) and less than .2 ohms DC resistance. If the amplifier sticks to one rail the autoformer will cause the primary mains fuse to blow protecting the speakers. It is an elegant solution to DC protection.

The inductance limits the autoformer from becoming a substantial part of the load for audio frequencies. As long as the high pass filtering for the amp is at a high enough frequency.

The autoformers themselves are incredibly linear, even the ones I've tested from McIntosh amplifiers from the mid 70's and earlier will pass a full power signal at less than .05% THD.

SNI's picture

200 mOhms is actually a lot in that part of an amp.

Best Regards


SpeakerScott's picture

Not really...that's still a damping factor of 40 for an 8 ohm speaker which is more than enough to minimize frequency response variation and not impact time domain performance in an audible significant way.

SNI's picture

I don´t agree.

jmsent's picture not just a function of the DCR of the autoformer. There's the feedback loop which effectively lowers the output impedance to very low values. JA has measured this in the review. The effective output impedance is on the order of .09 -.13 ohms at the 8 ohm tap...certainly more than adequate. I realize you don't like the amp, and I'm not here to defend it as I think it's overkill for a home audio system. But there's no disputing that it measures quite well in most respects. Your philosphical objections to autoformers not withstanding, what are your issues with it?

SNI's picture

My issues with autoformers is that you get high output impedance.
0,09 Ohms makes a DF @ 89, and that is not very much for a solid state amp.
So the McIntosh has the disadvantage of a low dampingfactor and on top of that it stil has a global feedback loop.
When using global feedback, you should at least have a higher DF than even non feedback amplifiers can achieve.
You can se it clearly on its power delivery.
There is not very much distortion, but power decreases rappidly with load.
That means when you call upon its power into a real speaker load, it will not stay linear at all levels.
Thus the non linearities will be amplitude related, and will not show on a THD measurement.
I really don´t like the idea of "hiding" an amps misbehavior behind a transformer, no matter what type it might be.

jimtavegia's picture

If you think of 6db per bit for dynamic range, one would think that 96db would be enough. Now I doubt there are many 16 bit chips made any more and 24 bit chips are so advanced and of such high quality and can playback more formats.

What I want is more samples per second and find that at 96khz there is just a much more smoother sound, more accurate to me and that is what I want to hear. I know mathematically that 192khz is better resolution, but my nearly 72 year old ears have a hard time hearing the improvement, but I'm sure it is there, probably. There is no mistake to me that 2496 is a great format for hearing what there is recorded in PCM. In my home studio I record everything at 2496 and some material at 24192.

DSD is even better, but now that is pretty much limited to downloads as no one I know is making affordable SACD players anymore. I wish they were. This Mac amp will handle anything you pass through it and, as the review showed, reveals flaws in poorly recorded material.

Bogolu Haranath's picture

Denon makes DCD-1600NE, which can play CD and SACD ........ MSRP $1,199 :-) ..........

jimtavegia's picture

I did not know that Denon had one. I was sorry to see Oppo go.


Ortofan's picture

... more likely to be found in the video department.
A few DVD/Blu-ray disc players have SA-CD compatibility and a set of RCA audio output jacks.
The $330 Yamaha BD-S681 is one such unit.

Dtb1180's picture

Did you compare this amplifier directly to your tubed McIntosh? Also have you heard the lower powered models that are not quad balanced and do they sound similar? I have owned tubed (MC275 mark 6) and solid state (MC252 I think) and they have a similar house sound. What do you think?

Dr. M.'s picture

Greetings, Thanks for your focused questions.I still own my wonderful MC275; of course with ability to swap tubes comparisons will change.My review comments do refer to prior extended listening to the MC275. Please see my question to Charlie Randall in the attached interview now posted, about the "McIntosh Sound." Some people hit on Mac for this- I view it as a strength.

No, haven't spent recent in-house time with prior solid-state McIntosh amps- only under show and shop conditions. Enjoy the long and winding Mac road! - Best, Sasha M.

Anwar's picture

Hi Sasha, you tested the MC462 with Harbeth M30.2. I have the MC452 and recently acquired M30.2. Which speaker taps you use and prefer for M30.2? Thanks.

JGlacken's picture

Hi Sasha,
I see we have the same dac. Have you tried the Dac direct to the 462 and if so is it compatible?
I am thinking of buying a 462, but want to check this out first.


granosalis's picture

I have Tannoy Canterbury GR with Nominal impedance 8 Ohms and Minimum Impedance 5 Ohms. Which output Autoformer tap should I use?

direstraitsfan98's picture

Hello, Mr. Matson, I finally made the plunge to purchase this amplifier based on your excellent and well written review of this product. Much appreciated, I look forward to seeing more McIntosh products looked at in the future. I would like to suggest Stereophile takes a look at the C2700 tube preamplifier, and the C53 or C70 solid state preamplifiers. Thanks for your consideration.