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McINTOSH
MC2102 TUBE POWER AMPLIFIER
MMcIntosh may not quite be the oldest name in audio, but it’s certainly the most revered and has been ever since Frank McIntosh built his first amplifier, ‘way back in 1949.
The reason for its immediate success was its Unity Coupled circuit design, which McIntosh invented, and for which he was granted a patent and which is still used in the MC2102. The Unity Coupled circuit made the McIntosh 50W1 one of the most powerful consumer audio amplifiers in the world at the time, but the real reason for its success was that it had the lowest distortion of any amplifier then available, and the widest bandwidth.
All this was possible because McIntosh had worked out how to deliver power from both the anodes and cathodes of his output
valves via special transformers with bifilar windings which needed only half the turns ratio required by conventional output transformers. This meant that for the first time, a consumer amplifier was able to deliver high power, low distortion and a flat, extended frequency response.
The Equipment
The MC2102 has a lot in common with the original McIntosh, though it was designed and engineered only recently by Sidney Corderman who was called out of retirement in 1997, having retired in 1993 after working for McIntosh for 42 years. The clarion call came because McIntosh wanted a unique product to mark the occasion of the company’s upcoming 50th anniversary in 1999.
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Corderman had joined McIntosh fresh out of MIT. The amp he designed was the MC2000 Commemorative Edition, which was also a limited edition model, with only 559 ever made. The amplifier was so successful that Corderman hung around to design the MC2102.
The MC2101 is rated at 100-watts per channel but the channels can be bridged, turning the MC2102 into a 200-watt monobloc. Actually, the channels can be joined together two ways, via a three-position slide switch on the chassis next to the input connectors (about which more later). The three positions are Stereo,
Parallel Mono and Bridged Mono. The MC2102 can be bridged to provide 200W mono into 16, 8, or 4-ohms, or the two channels can be run parallel to provide 200W into 4, 2, or 1-ohm. In the mono bridged mode, there’s a phase inverter dropped into the input of one of the channels, so one channel is 180 degrees out of phase and the speaker is connected between the two ‘hot’ output terminals. This gives a fully balanced amplifier where the two output transformers are essentially turned into a single centre-tap unit.
The MC2102 has eight valves per channel. Balanced input and inversion is handled by a pair of 12AX7s, while twin 12AT7s provide voltage amplification and driver functions.
Output valves are the famous KT88s (although you can use 6550s). The output transformers have a number of different taps, so they can be matched to 2, 4 or 8-ohm loads for stereo operation or anywhere from 1 to 16-ohms as a monobloc. In fact, the enormous output transformers make up most of this amplifier’s massive 40kg weight. McIntosh still winds all its own transformers in-house, using many of the original machines (though one suspects they’re as original as your great grandfather’s axe). Remember that to make these transformers, three transformer windings are required rather than the usual two. There are two primaries (one for the plates, one for the cathodes) and a secondary. The two primaries are spun bifilar (that is, two strands
wound together) for a close, turn- by-turn coupling. (Hence the name: unity-coupled output circuit.)
The power transformer is tapped for 100, 120 or 230V mains voltage, so you can use the amplifier anywhere in the world. In-rush current is controlled by thermistors, and the power supply uses a combination of four 1,000µF capacitors and a filter choke to ensure smooth clean d.c.
The most visible features of this amplifier are the two blue power meters on the front panel. In fact these meters (known as ‘blue eyes’ by McIntosh aficionados) are not on the front panel at all—they’re behind it, because the front panel is made from clear glass. All the writing on the front panel is etched onto the rear of the glass. This is a very difficult way to make a front panel (it takes three days because the glass is cut using a high-pressure water jet cutter and each of the 12 layers of ink is UV cured before the next layer is applied), but there’s a good reason, which is that the panel can be returned to ‘as-new’ with just a quick spray of Windex or any other ordinary glass cleaner.
Almost as visible are the two knobs on the front panel. The lefthand one controls the operation of the output level meters and the front panel’s backlighting (though why you’d ever want to switch it off is beyond me). The right-hand one is the power switch (on, off, remote). Like pretty much everything McIntosh makes, these are highly unconventional, because they’re not regular switches. Instead, they operate solid-state electromagnetic devices inside the amplifier which do the actual switching. The switches are not dissimilar to the reed switches used to connect doors and windows to burglar alarm systems, except that instead of using a permanent magnet to operate the switch, McIntosh winds a coil around the tube and uses d.c. current to energise the coil and create a magnetic field which in turn actuates the switch contact, opening or closing it as necessary.
Although valve amplifiers don’t really go into hard clipping like their
solid-state counterparts (one of the reasons why valve amplifiers sound better than transistorised amps when they’re operated close to their limits) McIntosh includes an ‘anti-clipping’ circuit it calls ‘PowerGuard’. According to McIntosh, this ‘provides real-time clipping protection without affecting power output or sound quality.’
The rear of the McIntosh is unusual because for each channel there are four WBT speaker terminals. Of these, one goes to the ‘negative’ speaker terminal, then you choose one of the three remaining terminals for the ‘positive’ connection, depending on the nominal impedance of your speakers. There are both balanced (XLR) and unbalanced (RCA) input connectors, with a switch to choose between them. The other switch on the rear of the McIntosh is what’s used to ‘join’ the two channels together, either in bridged mode or dual mono mode, as discussed previously. If you choose the bridged mode, not only does the power output capability increase to 200-watts, but also the minimum impedance the MC2102 can handle drops all the
M c I N T O S H
Brand: McIntosh
Model: MC2102
Category: Valve Power Amplifier
Suggested Price: $17,490.00 Warranty Period: Three Years*
Distributor: Castel Electronics Pty Ltd
Address:
121 Beaufort Street Preston
Victoria 3072
Tel: (03) 9484 3788
Fax: (03) 9486 3868 Toll Free: 1800 505 051
E-mail: general@castel.com.au Web: www.castel.com.au
For additional information, turn to page 114 and circle 0201 on our Reader Information Service Card.
*Only one year warranty on valves.
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way down to 1-ohm, a load that would be the death of almost all solid-state amplifiers. Oh, a note. Be careful with these WBT terminals, because they have a ‘double action’ thread, where the top nut tightens on banana plugs and the bottom nut tightens on cable or pin connectors. If you don’t loosen the top nut, for example, you won’t be able to insert plugs at all!
A complaint that’s becoming more common in audiophile (and other!) circles is that ‘They don’t make them like they used to.’
However true that statement might be about many hi-fi brands, it could never be said about McIntosh’s products because basically they’ve been building them exactly the same way for the last 50 or so years. While the company has upgraded circuitry as better components have become available (metal film resistors, polypropylene capacitors, etc) McIntosh has made absolutely no attempt to make its products ‘cheaper’. It doesn’t even produce a ‘budget’ line, for example.
Just in case I’ve given you the idea that McIntosh has been making valve amplifiers all these years, I should disabuse you of this, because it isn’t true. McIntosh started designing and building solid-state amplifiers almost the minute transistors became available, commencing with the C24 preamplifier in 1964. Interestingly, the company’s 1700 receiver, also produced in 1964, was a hybrid, but not the hybrid you’d expect. In this receiver it was the tuner section that used the valves: the preamp and amplifier sections were solid state!
It’s a source of some consternation to aficionados of McIntosh’s valve designs that the current McIntosh ‘look’ actually stemmed from a solid state model, the MC2505, which was the first separate solid state power amplifier ever made by McIntosh. This amp introduced the all-glass front panel, the illuminated output level meters, the Sentry Monitor circuitry and the McIntosh ‘autoformer’. I
should confess at this point that this amp was also the first McIntosh I ever experienced (I regret to say that I couldn’t afford to buy it.)
Listening Sessions
My McIntosh MC2102 came in its original shipping package, so I had to get it out myself (which revealed to me—and my chiroprac- tor—that it’s really a two-person job!) and then plug in all the valves. Generally, I’d imagine that McIntosh dealers will deliver and install the MC2102, so you won’t have to worry about this, but if you do, can I recommend you don’t handle the valves with your fingers? It doesn’t matter if you do use your fingers (otherwise dozens of valves I’ve replaced over the years would never have lasted as long as they did) but you’ll find that if you do, you’ll get fingerprints on them that could be hard to shift after the valves have heated up.
It’s often recommended that you use white cotton gloves (and indeed McIntosh provides a pair for you), but I find these can be slippery, making it tricky to grasp the valve without running the risk of dropping it. I used a new, dry ‘Chux’-style dishwashing cloth to grab mine. Just to be on the safe side, I’d install all the valves while the MC2102 is still on the floor (preferably carpeted) so that if you do drop a valve, there’s no chance of a breakage.
I am quite used to valve amplifiers running hot, which is nothing less than you’d expect, particularly if, like me, you’ve owned a few in the past, but I found that the MC2102 was like a small furnace! It turns out that the eight KT88s are driven with fixed bias, and because of the cathode arrangement, each one is driven by about 170-volts. When you factor in the added heat from the four 12AX7 input valves and four 12AT7 valve drivers, you’re looking at quite a handwarmer. After only a few hours of operation, the metal cage that protects the 16 valves became almost too hot to touch. (Actually very few
photographs of the MC2102 show this cage, because the amp looks so great without it, and you don’t really have to fit it at all if you don’t want to. I suppose it depends on your home situation. If, for example, children are likely to have access to the amplifier, I’d recommend ALWAYS using the cage.) My understanding was that the KT88s used in the MC2102 were made for McIntosh by Svetlana (Russia) but the ones in mine seemed to be made in China. I love the sound of KT88s (NOS rather than newly manufactured), but if you’re a 6550 person, McIntosh is happy for you to substitute.
McIntosh is not unaware of the problem with heat, because in its (absolutely excellent!) instruction manual, it suggests you may care to cut a hole in the table, bench or shelf that’s supporting the MC2102, to allow air to come up from immediately underneath the amplifier. This is a great idea unless, like me, you put the MC2102 on a polished antique table! Needless to say, if you’re one of those people who likes positioning their amplifier on the floor between their speakers, I certainly would not recommend this if your floor is carpeted.
When I was burning the MC2102 in (an entirely appropriate expression in this case!) I kept an eye on the power meters, because the test discs I use for burn-in have a wide range of signals, and I was interested to see how accurate the meters were, despite the fact that it’s my personal opinion that power output meters on amplifiers are of very little practical (if any!) use— though I suppose they could alert you to the presence of infrasonic or ultrasonic signals. It seemed to me that the meters responded very fast and very accurately with tonebursts, impulses and pink and white noise, though I didn’t have access to any test equipment to verify the exact speed of the needles, or the calibration accuracy of the meter markings. I’d have to warn that the accuracy of the meters would also depend to a large extent on the speakers you use, and the particu-
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