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Sidney A. CordermanA Corderman classic, the original MC275 of 1962
enjoyed a remarkable 12-year run. It was reissued
as a commemorative edition in 1990 (pictured). The supplied tubes are the same ones used to test
the MC2000 prior to packing. They are placed in a
specially designed case for transport. The MC2000 includes a removable cage that
protects the tubes as well as curious fingers.
The amp is shipped with the cover off.The styling of the MC2000 complements the look of
current McIntosh components. The front window
showcases the warm glow of the tubes.
A Brief History
T
he MC2000 New Millennium Edition Tube Power Amplifier
is the crowning achievement of legendary McIntosh designer
Sidney Corderman. Responsible for some of the worlds greatest
tube amplifiers, Mr. Corderman has saved his best for last.
Equal parts new and venerable technology, the MC2000 com-
memorates the 50
thanniversary of McIntosh Laboratory. Behind
its stunning facade, rich materials, and meticulous engineering
is a powerful dual monoblock amplifier that delivers 130 watts
per channel with extremely low distortion.
Every detail -“ the ceramic tube sockets with air-pipe cooling,
the polyester capacitors, the kid gloves that protect the hand-
rubbed gold finish -“ contributes to an ownership experience not
likely to be surpassed.
A small plaque on the amplifier pays tribute to Mr. Corderman.
After registering, owners receive a certificate of authenticity that
indicates their models production number and the total number
of models produced.
The 21st century promises fundamental changes in technology
and manufacturing. But as the MC2000 so emphatically states,
McIntosh products will forever be distinguished by a completeness
of design, implementation, and craftsmanship rivaled by no others.
Frank McIntosh, Gordon Gow,
and Maurice Painchaud formed
the original McIntosh Engineering
Laboratory. Their goal: produce
the first High Fidelity audio
power amplifier -“ one that would
reproduce the entire audio range
(20Hz-20kHz) with low distortion.The McIntosh 50W1 made its
debut in 1949. It would take
competitors nearly 20 years to
match its performance.
In 1951 the brilliant MIT engi-
neer Sidney Corderman joined
the company as Chief Engineer.
He was directly involved with thedesign of all McIntosh products
until his retirement in 1993.
Mr. Corderman was coaxed out
of retirement in 1997 and began
designing what would become
his finest achievement: The
MC2000 Tube Power Amplifier.
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Words of \braise
A lmost 50 years ago Frank McIntosh and Gordon Gow
invented and patented the McIntosh Unity Coupled Output
Circuit. Two features differentiate it from other designs. First,
the output tubes deliver power from both their plates (anodes)
and their cathodes, not from their plates alone as in conven-
tional circuits. Second, the output transformers two bifilar
primary windings give it one-half the turns ratio of conven-
tional transformers, equating to one-fourth the impedance
ratio. This allows a close coupling of the primary and secondary
windings, resulting in wide bandwidth, flat frequency response,
and low distortion.
Overview
The MC2000 contains two identical channels with separate
audio circuits, power supplies, and power transformers. Each
channel has three amplification stages: input/phase inverter,
driver, and output. The MC2000 uses the famous Unity Coupled Output Circuit
with eight KT88 output tubes (four per channel) in a push-pull
parallel configuration. Large transformers with grain-oriented
silicon steel cores allow full power output down to 17Hz. As each channel is identical, the following description will
address a single channel.
The Output Stage
The KT88s operate with fixed bias. Adjustments are needed
only when the tubes have aged or been replaced. Because the
tubes are additionally loaded in their cathodes they require a
large drive signal (approximately 170V) for full output. This
signal is provided by the 12AT7 driver. Boot-strapping the
driver to the plate winding of the output transformer results
in greater amplification than otherwise possible. The Driver Stage
The driver stage is fed by the 12AX7A input/phase inverter. A
resistance-capacitance step network couples these stages and
minimizes low-frequency phase shift. The phase inverter has
no coupling capacitors so no additional low-frequency phase
shift is introduced. Emitter follower stages at the plates of the
12AX7A increase bandwidth.
The Input/Phase-Inverter Stage
Mode selectors at the rear of the chassis choose balanced or
unbalanced inputs as well as input sensitivity (1.2V or 2.5V).
The selectors operate Silent Electromagnetic Switches located
adjacent to the input circuits. When the balanced input is used
a second 12AX7A receives the balanced signal. One section of
the driver tube is a cathode follower that passes the positive
phase signal. The other section inverts the negative phase signal.
The two outputs are combined and fed to the input/phase-
inverter stage. Common mode rejection is greater than 60dB
at middle frequencies.The Feedback Circuit
Global negative feedback is taken from the output transformer
secondary to the cathode of the input stage. Conventional
wisdom cautions against using negative feedback, especially
in tube amps where instability is a real concern. However, the
MC2000 is designed in consideration of negative feedback,
the many benefits of which are: lower distortion and noise,
flatter frequency response, faster rise time, and higher damping
factor. A common misconception is that the feedback signal
is delayed and therefore introduces time distortion. This is not
so in a properly designed amplifier. In fact, the time delay of
the entire MC2000 circuit is less than 2 microseconds.
The Power Supplies
Each power transformer has two tapped primary and three
secondary windings. The primary can be connected for 100V,
120V, or 230V. A thermistor cushions inrush current. A power
MOS FET is used as an active filter to ensure extremely pure
DC power. A medium-voltage secondary winding feeds the
negative bias voltage supply and a low-voltage secondary
feeds the filaments of the output tubes, the driver tube, and
indicator lamps. This same winding feeds regulated DC power
supplies for the meter circuit as well as the heaters of the
12AX7A input stages.
The Meters
Individual meters monitor the power output of each channel
and include a hold mode that briefly indicates the highest
power reading. The meters also serve as indicators when set-
ting the bias for the output tubes.
The MC2000 is breathtaking in the way it
resolves a recordings most subtle details.
This level of resolution matters -“ it makes
listening much more involving when you can
hear every nuance of a pianists phrasing;
the slow, natural decay of each note; every
quiver of a sopranos vibrato. The MC2000s
spatial resolution is stunning.
Other amps-¦separate the great
recordings from the good and the
not-so-hot. But many tend to do so
in a clinical way, as if the gear is
some kind of machine for resolving
detail rather than for re-creating
music. The MC2000, to a remarkable
degree, combines resolution and
musicality.What the MC2000 offers,
in addition to its sound,
is spectacular styling and
the satisfaction of owning
what is surely the greatest
McIntosh tube amplifier
ever produced. Stereophile
contributing
editor Sam Tellig was the
first critic to review the
McIntosh MC2000. His
review appears in the
November 1999 Sams
Space column. These
excerpts are used with
permission.
\fechnical Description
NOVEMBER 1999 $6 95 US $7 95 CAN
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