4
One of a Kind
The MC901 Dual Mono Amplifier has been
designed to be the ultimate solution for bi-amping
Loudspeakers. It’s the best answer in the quest to
capture the harmonic beauty of Vacuum Tubes for
a Loudspeaker’s mid and upper registers while still
having an abundance of power dedicated to the power-
hungry woofers. To bi-amp in the past, two separate
Amplifiers were required, but now the MC901 does
the work of two separate Amplifiers with its optimized
combination of a Tube and a Solid State Amplifier
happily co-existing as a single optimized instrument.
Previously, crossover points would have to be handled
outside of the Amplifier and a lot of trial and error
would be required to properly setup two Amplifiers
that were not designed to work together.
The MC901 is the perfect solution for bi-amping
speakers. 300 Watts of Vacuum Tube power are
available to drive your Loudspeaker’s midranges and
tweeters. Vacuum Tubes do not perform optimally
when amplifying frequencies that are not used by
the Loudspeaker. To maximize the Tubes’ power, the
MC901’s internal, adjustable crossover assures the
Tubes will only be powering the frequencies that the
Loudspeakers will be reproducing. With the MC901,
the Tubes will not be challenged or overloaded by
low-end reproduction because the Solid State section
has 600 Watts dedicated to driving the low end, and
the adjustable filters assure that each Amplifier section
handles only the frequencies that they are intended
to amplify. Full power of each Amplifier section
is available whether you are using 2, 4 or 8 Ohm
Loudspeakers thanks to our Unity Coupled Circuit
Output Transformer and Autoformer™.
McIntosh’s Unity Coupled Circuit Output Transformer
solved problems that had long plagued Vacuum Tube
Amplifiers. By employing a complex hand-wired
transformer design, the Unity Coupled Circuit Output
Transformer turned what had been a problem of
capacitance between two wires into a configuration
where the two wires support the transformer’s
performance. Furthermore, the complete coupling of
both halves of the transformer prevents the collapse of
the magnetic field, which is an issue for other Vacuum
Tube Amplifier designs. The Unity Coupled Circuit
also eliminated the switching error between positive
and negative halves, freeing the Tube Amplifier of a
sloppiness heard in other unsuccessful configurations.
On the Solid State side, the MC901 utilizes our
Autoformer, which provides the optimal method of
connecting a Solid State Amplifier to a Loudspeaker
of virtually any impedance. The McIntosh Autoformer
provides full power to the Loudspeaker regardless if
it has 2, 4 or 8 Ohm impedance while offering DC
current protection to the valuable Loudspeakers. The
Quad Balanced design of the MC901 works with
the Autoformer to combine two out of phase audio
signals. The two out of phase signals are magnetically
combined in the Autoformer where one signal is
inverted back into phase with the other signal. During
this process, any distortion in either signal will be out
of phase with the other signal and cancelled. While
distortion is cancelled, the power will be summed
due to the unique properties of the hand-wiring of the
McIntosh Autoformer, and the newly combined signal
will be twice the power of the individual signals.
Power Guard
®
monitors and adjusts the input signal in
the 600 Watt solid state amplifier section in real time,
then makes unobtrusive adjustments to prevent harsh
sounding distortion and potential speaker damaging
clipping. The 300 Watt Vacuum Tube amplifier section
of the MC901 breaks new ground as it’s our first
amplifier to feature our new Power Guard Screen Grid
Sensor™ (SGS) technology. Power Guard SGS™
helps prevent premature Vacuum Tube failure by
monitoring the screen grid current in the KT88 output
Vacuum Tubes. If the current becomes too high, a
circuit in Power Guard SGS is activated which then
dynamically attenuates the input signal in real time to
keep the Vacuum Tubes operating at safe levels.
The Solid State and Tube Amplifier sections of the
MC901 are engineered to function in tandem, with
each specifically designed to perform its role. Fine
tuning your system is made simple with variable
Low Pass and High Pass Filters. This allows you
to compliment the crossover settings of your
Loudspeakers and maximize the power available to
each frequency range. Relative gain levels for each
section can be adjusted from -6dB to + 3dB, or you
can connect a direct feed to each Amplifier section and
bypass all the filters. This is perfect if you have room
correction and crossovers external to the MC901.
McIntosh is uniquely positioned to create the MC901.
McIntosh has a 70-year track record of producing
award-winning Solid State and Vacuum Tube
Amplifiers utilizing our patented technologies. The
MC901 builds upon this foundation and expands this
legacy of quality and cutting-edge innovations. That is
why only McIntosh could have developed the one-of-
a-kind MC901.
