Mcintosh mc2102 schematic

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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MC2102 TUBE POWER AMPLIFIER

equipmentreview

McINTOSH

M

McIntosh 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

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21

wound together) for a close, turn­by-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

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

McINTOSH

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: [phone]
Fax: [phone]
Toll Free: 1800 505 051
E-mail: [e-mail]
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.

equipmentreview

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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

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-

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 chiroprac­tor—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