How Big Things Do Come In Small Packages
So, what do you think of right away when you hear "THE American motorcycle" or "THE American soft drink"? Something like Buell or Dr. Pepper? – No, I didn't think so, either! And now comes THE American tube amplifier.
The whole big, grand show, the unbridled exhibitionism of power, this "Hey, look-at-us! We can do it all, just forget the discretion." Now that's something the Americans have truly got down to a fine art. Understatement? Well, that’s just European skeptical, even moody, reserve. Show us what'cha got, and please don't forget to drive the point home with pride – that's how it goes!
Well, maybe it's high time to rethink this whole matter.
Now, there are quite a few speakers on the market that aren't even remotely content with being fed 75W, not to mention those to which that's merely a tickle or a twitch. Among them, there are pumped-up versions to be found that you actually have to use a big, fat crowbar of an amplifier with to get their attention and teach them even a few basic manners. And, if you’re not sure about the power consumption consequences in that case, you can always negotiate a special electricity rate with your local power company. You see, what we're talking about here are speakers with audiophile-grade super-soft rubber surrounds, fitted with super-complex dividing networks, themselves equipped with super-sharp absorption circuits, about super-compact spatial imaging speaker miracles achieved with absurdly low tuned bass at precisely no cabinet volume at all, about 1.whatever Ohms speakers with umpteen polypropylene membranes, about exotic large-area planar speakers, all of which are only happy with copious gobs of power. With this build configuration, the power required suddenly jumps to stratospheric levels, yet at the same time the stability of the amp heads right down into the cellar (I almost said "down the tubes", but …). During all this, a few hundred watts are eaten up faster than most other amps can even supply to begin with.
I myself don't own these kinds of power suckers (anymore). Quite the contrary, in fact: For instance, my Dynavox 3.2 speakers run great even with just a small amount of power, even though they can actually handle 100 W – but with a 96 decibel power efficiency rating a rather theoretical figure. In any case, I haven't yet pushed them to their limit. When it comes to efficiency, the starting point for me is the Stereofone Dura (test report in image hifi issue no. 63), a six-ohm dipole speaker with an efficiency of just under 90 decibels. Even with a speaker like this one, the MC-275 won't have any problems at all in the vast majority of cases. There's no doubt about that. There's hardly any type of music that would present this setup with any kind of serious issues. It thunders and projects, attacks and pumps, massages and flows just as it ought to; that is, cleanly and subtly, with enough drive and push – yet with extreme finesse. In this case, the 275 would already need to be bathing a very large room with sound – perhaps feeding some power sucker from speaker hell – to reach its limits.
It's all really quite amazing: The good old/new McIntosh sits there like a massive iron hulk, providing power with brilliant flying colors with even room to spare. So why, then, does it suddenly occur to me: Don't its tubes glow just a bit more than usual? I mean, wouldn't that extra glow be, in view of the stainless steel chassis, the flat black transformer housings and the unavoidably obvious model logo, even right, proper and reasonable? Well, of course, it's clear that the tube "glow level" is determined by the technology. But when even in an only somewhat dim environment, the eleven cleanly lined up glass tubes light up the room like a Christmas tree (anyone for Christmas in spring?), then there's still something subtler to be desired. At any rate, what I certainly don't miss on the MC-275 is the usual McIntosh blue display. If it had one, I'd have shut off that bluish glow off already, anyway. Quite honestly, I'd really prefer just small "ON" indicator lamp, just in case the sun is shining in my room and no music is playing. OOPS! Forgot to turn it off, again. That kind of thing, you know. You see there is absolutely no hiss, hum or extraneous noises with this power amplifier. Without a signal, the thing is essentially as quiet as a (dead) mouse. Almost too quiet, even dangerously so, if you get my drift.
What I like less are the screw-down terminal blocks for the stripped speaker cable ends: Just as in the old days, the Phillips screws and the captive washers squish the cable ends. The best thing to here is to put terminal lugs (crimp, solder) on the end of the cables before hooking up the speakers. Well, OK, I've always got an appropriate screwdriver handy, and the 16 Ohm contacts will certainly please the true audio nuts. Nevertheless, as a practical matter, the connections are too small and fiddly to work with easily. Historically speaking once again, the double blocks of gold-plated output binding posts may seem to be indispensable, but I can't find anything positive to say about this old-fashioned, dated setup. A truly traditional, perhaps habitual, anachronism. But who knows, perhaps the fifth edition of this unit will offer some improvements in this area (dream on, Brockmann!) Despite this downside, the major effort invested in making this unit easy, secure and safe to transport is impressive. The packaging system is the only thing about the McIntosh MC-275 that somehow seems European to me – something that I, of course, view as positive feature. It's unreal: Even the smallest foam pieces in the admirable packaging system have their own part numbers(!) in case one might happen to go missing and you'd need another (unlikely to happen to the first owner, but you never know) or the outer carton is swept away during the next flood (you know, Monaco, Sylt and Hawaii are all insecure areas in this respect!)
After being removed from the carton and switched on for the very first time, the MC-275 takes a few hours to "settle in" the tubes and "limber up" the components and get them ready for action. But we're all used to all that. So, for the first 15 to 30 hours of operation, you let the beast do a few stretching exercises in order to train its fine-motor skills and agility. After that, it's essentially domesticated and accepts whatever it gets from the pre-amp tamely and obediently. And, by then, what seems to have started out as bit dim, slow, less-defined process at first will have truly become an alert, wide-awake certainty: Despite all its instantaneous hard and heavy power, the McIntosh has an amazingly nimble way of moving right along. The dreaded bull-in-the-china-shop effect doesn’t manifest itself; there's no clumsy, awkward thrashing about at all. In fact, the MC-275 has enough reserve capacity to last until Judgment Day – assuming the speaker is correct – and the option to increase the power with a mono switch up to double the original amount, that is, to 150 W, a step that moves its horizons a bit more upward and outward. By plus three decibels to be exact.
But be that as it may very well be: This power amplifier is a stunningly realized piece of massive equipment, really "dynamite" as the Americans say, all well formed in metal and glass. And where the so-constructed MC-275 really shows itself at its best is in its definite, confident uniformly flowing appearance combined with and complementing a magnificent broad range, crisp clarity, extremely solid, confident tonality that is anything but indecisive, timid or vague. It knows what it has to do and it does it. Case closed! In short: String-instrument groups transparently "soar" through all their waves and surges, brass sections have the requisite sonorous "bite" while blaring up and down/in and out, and the "punch" and "impact" of drumming and percussion of all types is also a wonderful listening experience. Singers have their exact sound and individual timbre, have "presence", and are "touch-me" clear in the vocal passages, which are readily understood. There's nothing smeary, blurred, indistinct or veiled with the McIntosh MC-275.
Key Device Information
Tubes: 4 x KT-88, 4 x 12AT7, 3 x 12AX7A
Power Rating (manufacturer's specs): 2 x 75 W channels; 1 x 150 W when bridged into a single mono channel
Inputs: 1 x symmetrical (XLR), 1 x asymmetrical (Cinch/RCA)
Outputs: Speaker connection terminals with transformer terminals for 4, 8 and 16 Ohm load impedance
Special features: Separate input levels for controlling each channel (asymmetrical input), mono operation possible, input device selection
Dimensions (L/W/H): 43/18/32 cm
Weight: 30 kg
Warranty period: 24 months
Price: 3,980 euros
For more information, go to
Circuit Engineering at its best
With the MC-275 and its predecessors – especially the MC-30 and MC-240 – there's no doubt Gordon Gow and Frank McIntosh inaugurated a new era in tube amplifiers. That's because, their innovative, unique - to this very day - circuit engineering solved with one stroke of genius two baffling problems that had always been vexing system designers.
One on hand, it simply had to do with performance: If you wanted more than 30 or 40 W of clean output, then the result was likely going to be a 50 kilo (over 100 lbs.) cabinet on your table, a situation that McIntosh and Gow also had to envision with their very first amplifier. Still made under the name CRE ("Consulting Radio Engineering"), this unit, along with six 807 tetrodes did, in fact, provide 50 W at the speaker connection terminals, yet it weighed 62 kilograms (almost 140 lbs.). The lesson that you could probably sell such super heavy, massive high-performance amps to studios but not likely to end users was quickly learned.
On the other hand, the second problem had to do with quality. Back then, this problem was primarily documented through distortion measurements based on the required frequency response. New observations, now really based on true "high fidelity" considerations, plainly demanded a broad frequency range or band of from 20 Hz to 20 KHz, and all that had to be crystal clear and well-defined, even at very low frequencies. And it was exactly there where the most highly efficient, but also distortion-prone B amplifiers, caused the greatest problems. Using only B or what was known as AB2 operation seemed to be very attractive to the efficiency-obsessed tube technology of its day. In fact, if necessary with two standard tetrodes such as the extremely popular 6L6 in a push-pull arrangement it was possible to squeeze 50 W out of the system, but with less-than-ideal "hi-fi" results in terms of actual measurements.
The road out of this dilemma was long and hard. It first led to a small amplifier called the "50-22", which didn't look impressive, but was an important milestone on the way to something that you really should, in view of the options available from tube technology, call essentially perfect, even by today’s standards. The key, pivotal element of the famous McIntosh technology was and remains the output transformer, which now was significantly more complex than previously and thus demanded far more precise assembly than ever before. From then on, the aim was to use three primary windings, two of which to had to be bifilar wound (windings doubled-back upon themselves) and symmetrically arranged with respect to each other. Both the cathode and anode and even the screen grid for both end tubes were now connected to the output transformer. The result was a contrivance that was somewhat awkwardly described as a cathode negative feedback and anode/screen grid cross coupling or even "feed forward of opposing phases". Of course, the result certainly spoke volumes for itself: 50 W coming out of only two 6L6Gs with less than 1% distortion – even at full power and all the way from 20 Hz to 20 kHz. For the technically accomplished and aware tube freaks at the time it was nothing less than a seismic event, one which may be considered to be the basis for future famous units from the talented and persistent team of Gow/McIntosh. Given that, it's worth taking the time to do to more than just gape at the output stage of the 50-2. That's because on the input side, it also exhibits amazing electronic elegance and, at first glance, combines structurally simple yet highly effective tube technology with absolute symmetry. Its fame as a milestone is fully justified!
In the MC-275, the brilliant McIntosh design goes even a major step further. With a solution known as a type of "bootstrap winding" for the anodes in the driver-stage tubes – originally a 12AZ7, now a 12AT7 cathode follower – the complexity of the output stage has increased once more with the driver now integrated in the end-tube/transformer assembly. The two heavy-duty output transformers set up to provide 4, 8, and 16 Ohm loads have now reached a point where they may be considered masterpieces in transformer development, a design that also even has to add yet another independent negative feedback winding on the secondary sections of the transformers. So, it's really, as they say, "got all it together" in more than one way and yet even with all-over negative feedback design, the McIntosh could give the impression of being an obsessively linearized power amplifier amplifier, which certainly because of, or perhaps even despite being so, is famous for being one of the finest-sounding tube power amplifiers available from anyone, anywhere. And the 75 W coming out of two KT88s per channel is certainly something notable, even spectacular. And don't forget, that's with less than 0.5% distortion (ultra-low!) at full power! At the same time, the current MC-275 can claim the closest kinship to the original model because it boasts the magnificent, justifiably famous and, as such, highly sought KT88 from MOV inserted its sockets. Because of output-tube problems, earlier versions of the MC-275 – after all, there have been four versions of it available so far – used the related but not quite so resilient 6550. For many years, really usable KT88s were hard to "scare up", a situation that MC-275 users could really tell a story or two or three about …
The thing to keep in mind would be that the MC-275 has speaker connections with lifted ground, which means that the negative "Com" connection has nothing to do with the main circuit ground. All versions of the MC-275 have the option of switching both channels to mono-bridged, single-channel operation and then allow thorough enjoyment of the resulting total 150 W. Directly behind the (selectable) symmetrical inputs there sits a 12AX7 (ECC83) in its socket, followed by a direct-current linked phase shifter, a symmetrically arranged triode system with another 12AX7. McIntosh used to employ a powerful double-triode (model 12BH7) as its voltage amplifier, but this assignment has been taken over by the two systems in a 12AT7 (ECC81). The signal phases go through linked capacitors to the already mentioned cathode-follower driver stage. Things are bit simpler when it comes to the power supply: Here, a single fat transformer provides all the supply voltage, including the voltages for tube heating. A filter coil, hidden underneath the chassis, works in tandem with a whole arrangement of capacitors to handle the reciprocally decoupled anode voltages for the individual stages of the amplifier. Beyond this, additional miniature fuses are intended to prevent the worst in the worst-case scenario, although due to its design and operation McIntosh circuitry is anything but a "tube eater". By the way, even if from a purely technical point of view the power amplifier is not necessarily dependent on the most precise tubes when it comes to their being matched in terms of quiescent current, in actual practice the MC-275 will also benefit from having all tubes within the closest spec tolerances as possible. Furthermore, good KT88s made in Russia present no real procurement problem any more. To be on the safest side, order the neat-looking, original-equipment set with the McIntosh logo on them.