The MC901 is a monoblock amplifier that drives a single speaker. But it is unlike any other monoblock amplifier. What makes the MC901 so unique is that it's two amplifiers combined into one. Adding to the uniqueness is that each amplifier is of differing design philosophies: the MC901 consists of a 300 Watt vacuum tube amplifier attached to a 600 Watt solid state amplifier on one unified chassis.

The 300 Watt vacuum tube portion powers the speaker's mid and upper drivers via eight KT88 output tubes, plus four 12AT7 and two 12AX7A signal tubes; the solid state section delivers 600 Watts of dedicated power to the power hungry woofers. The 300 Watt vacuum tube amp in the MC901 uses McIntosh's patented Unity Coupled Circuit output transformer to deliver its full 300 Watts into almost any speaker regardless if it has 2, 4 or 8 Ohm impedance. Similarly, the 600 Watt solid state amp delivers its full 600 Watts into a 2, 4 or 8 Ohm impedance speaker via their Autoformer™ technology.

Vacuum tubes do not perform at their best when they are amplifying lower frequencies that are not being used by the loudspeaker. With the MC901, the vacuum tube amp will not be burdened with low end reproduction as the solid state section will drive these frequencies. The two amplifier sections of the MC901 are designed to work together in a synergistic relationship and are specifically engineered to assure that each section only amplifies its intended frequencies. Each amplifier section has its own discrete power supply so neither siphons power or performance away from the other. All of this results in easy bi-amping with unparalleled performance and sound reproduction from your speakers.

Prior to the MC901, bi-amping a speaker required two separate amplifiers. It also required an external crossover, along with a lot of trial and error, to properly configure the two detached amplifiers so they worked together as best as possible. The MC901 solves this issue thanks to its internal, adjustable crossover with the controls easily accessible on the top of the unit. These adjustable crossover filters allow you to optimize the performance of both amplifier sections to your listening preferences. Relative gain levels for each amplifier section can be adjusted from -6dB to + 3dB. A direct feed can also be connected to each amplifier section, thus bypassing the filters.

Like virtually all McIntosh amplifiers, the MC901 features an iconic "McIntosh Blue" Watt meter, which has come to be recognized around the world as a symbol of quality home audio. And just like the MC901 itself is a new design, so too is its meter with the introduction of McIntosh's new DualView™ Power Output Meter. The DualView meter features two of their traditional, fast responding mechanical meters stacked above and below each other in a single meter window; one meter is dedicated to the 300 Watt vacuum tube amp and the other to the 600 Watt solid state amp. Each meter operates independently of the other and displays the real time power reading of each amplifier section.

While an entirely new design, the MC901 comes with the technology one would expect from a McIntosh amplifier:

• Power Guard® that 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.
• Power Guard Screen Grid Sensor™ (SGS). The 300 Watt vacuum tube amplifier section of the MC901 breaks new ground as it's McIntosh's first amplifier to feature their new Power Guard 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.
• Sentry Monitor™ observes the output current and shuts the amplifier off if it ever exceeds safe limits.
• Quad Balanced design that cancels virtually all noise and distortion that may have crept into the audio signal.
• Power Control that can send power on/off signals to other connected McIntosh components for easy system power up and shutdown.
• McIntosh patented, gold-plated Solid Cinch™ speaker binding posts that easily and securely attach the speaker cables.
• McIntosh Monogrammed Heatsinks™ that are connected to advanced high current output transistors efficiently cool the solid state amplifier section.
• McIntosh Power Management System that will turn the entire unit off after a set amount of time when no input signal has been detected.

Specifications:

• Power Output per Channel:  Solid State section: 600 Watts @ 2, 4 or 8 Ohms / Vacuum Tube section: 300 Watts @ 2, 4 or 8 Ohms
• Number of Channels:  1
• Total Harmonic Distortion:  Solid State section: 0.005% maximum harmonic distortion at any power level from 250 milliwatts to rated power, 20Hz to 20,000Hz / Vacuum Tube section: 0.5% maximum harmonic distortion at any power level from 250 milliwatts to rated power, 20Hz to 20,000Hz
• S/N below rated output:  Solid State section: 122dB / Vacuum Tube section: 112dB
• Dynamic Headroom:  Solid State section: 2.5dB / Vacuum Tube section: 1.2dB
• Damping Factor:  Solid State section: >40 / Vacuum Tube section: >18
• Rated Power Band:  Solid State section: 20Hz to 20kHz / Vacuum Tube section: 20Hz to 20kHz
• Frequency Response:  Solid State section:  +0, -0.25dB from 20Hz to 20,000Hz,  +0, -3dB from 10Hz to 100,000Hz / Vacuum Tube section:  +0, -0.5dB from 20Hz to 20,000Hz,  +0, -3dB from 10Hz to 70,000Hz
• Remote Power Control:  Yes
• Multi-Channel DB25 Cable:  N/A
• Speaker Binding Post Type:  Patented Solid Cinch™ Speaker Binding Posts
• Circuit Configuration:  Solid State section: Quad Balanced / Vacuum Tube section: Unity Coupled
• Circuit Design:  Solid State and Vacuum Tube
• Mono Bridge:  No
• Mono Parallel:  No
• Output Type:  Solid State section: Autoformer™ / Vacuum Tube section: Unity Coupled Output Transformer
• Meters:  DualView™ Power Output Meter
• Meter Light Switch:  Yes
• Balanced Input:  3 (1 Solid State, 1 Vacuum Tube, 1 Composite)
• Front Panel:  Glass
• Illumination:  Direct LED
• Dimensions (W x H x D):  17-1/2" (44.45cm) x 13-1/4" (33.7cm) (including feet) x 29-1/2" (74.9m)
• Weight:  180 lbs (81.6 kg) / Shipping Weight:  200 lbs (90.7 kg)