MCINSTOSH MC 901

Dual Mono Amplifier Pair

The ultimate solution for speaker bi-amping: a 300 Watt vacuum tube amplifier and a 600 Watt solid-state amplifier in a single chassis.
The vacuum tube section powers the mid and high drivers.
The solid-state section powers the high-power woofers.
DualView™ Power Meter

McIntosh has been perfecting vacuum tube amplifiers since the 1940s and solid-state amplifiers since the 1960s. From this heritage comes a truly unique home audio amplifier, the ultimate solution for speaker bi-amping: the McIntosh MC901 Dual Mono amplifier.

The MC901 is a monoblock amplifier that powers a single speaker. But it’s different from any other monoblock amplifier. What makes the MC901 so unique is that it combines two amplifiers in one. Even more special is the fact that each amplifier follows different design philosophies: the MC901 consists of a 300 Watt vacuum tube amplifier paired with a 600 Watt solid-state amplifier in a unified single chassis.

The 300 Watt vacuum tube section powers the mid and high drivers of the speaker through eight KT88 tubes, plus four 12AT7 signal tubes and two 12AX7A tubes; the solid-state section provides 600 Watts of power dedicated to the high-power woofers. The 300 Watt vacuum tube amplifier in the MC901 uses the patented Unity Coupled Output Transformer, the same technology McIntosh was founded on in 1949, to deliver its 300 Watts to virtually any speaker, regardless of impedance (2, 4, or 8 ohms). Likewise, the 600 Watt solid-state amplifier delivers its full 600 Watts to a speaker with 2, 4, or 8 ohm impedance thanks to our Autoformer™ technology.

Vacuum tubes don’t perform their best when amplifying low frequencies that the speaker doesn’t use. With the MC901, the vacuum tube amplifier is not burdened with reproducing the low frequencies, as they are handled by the solid-state section. The two sections of the MC901 are designed to work together in a synergistic relationship and are specifically engineered to ensure each section amplifies only the frequencies for which it is intended. Each section has its own discrete power supply, so no power or performance is drawn away from the other. This results in easy bi-amping with unparalleled performance and sound reproduction from your speakers.

Before the MC901, bi-amping a speaker required two separate amplifiers. An external crossover was also necessary, along with a lot of trial and error to properly configure the two separate amplifiers to work best together. The MC901 solves this problem with its built-in adjustable crossover, with controls conveniently located on the top of the unit. These adjustable crossover filters allow optimization of performance for both amplifier sections based on personal listening preferences. The relative gain levels for each section can be adjusted from -6 dB to +3 dB. It is also possible to connect a direct feed to each section of the amplifier, bypassing the filters.

Like almost all McIntosh amplifiers, the MC901 features the iconic "McIntosh Blue" power meter, which has become a symbol of home audio quality worldwide. And just like the MC901 is a new design, so is its meter, with the introduction of the new DualView™ Power Meter. The DualView meter consists of two traditional fast-response mechanical meters, stacked one on top of the other in a single meter window; one meter is dedicated to the 300 Watt vacuum tube amplifier, and the other to the 600 Watt solid-state amplifier. Each meter operates independently of the other and shows the real-time power reading for each section of the amplifier.

Although it is a completely new design, the MC901 offers the technology you would expect from a McIntosh amplifier:

• Power Guard®, which monitors and adjusts the input signal to the 600 Watt solid-state section in real-time, making discrete adjustments to prevent hard distortion and clipping that could damage the speakers.
• Power Guard Screen Grid Sensor™ (SGS). The 300 Watt vacuum tube section of the MC901 marks a new milestone, being the first amplifier to feature the new Power Guard SGS™ technology. Power Guard SGS helps prevent premature tube failure by monitoring the screen grid current in the KT88 tubes. If the current becomes too high, a Power Guard SGS circuit is activated, dynamically attenuating the input signal in real-time to keep the tubes at safe operating levels.
• Sentry Monitor™, which monitors the output current and shuts down the amplifier if it exceeds safe limits.
• Quad Balanced Design, which virtually eliminates any noise and distortion that might be introduced into the audio signal.
• Power Control, which sends on/off signals to other connected McIntosh components to make powering up and down the system easier.
• Solid Cinch™ Gold-Plated Speaker Terminals, which securely and easily attach the speaker wires.
• McIntosh Monogrammed Heatsinks™, connected to the high-current output transistors, efficiently cooling the solid-state section.
• Energy Management System, which shuts down the entire unit after a set period of inactivity when no input signal is detected.

Electronic Specifications:

• FTC Power Output

  • Solid-State section: 600 W
  • Vacuum Tube section: 300 W

• Power Output per Channel

  • Solid-State section: 600 W into 2, 4, or 8 ohms
  • Vacuum Tube section: 300 W into 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 20kHz
  • Vacuum Tube section: 0.5% maximum harmonic distortion at any power level from 250 milliwatts to rated power, 20Hz to 20kHz

• Signal-to-Noise Ratio 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 20kHz
    • +0, -3dB from 10Hz to 100kHz
  • Vacuum Tube section:
    • +0, -0.5dB from 20Hz to 20kHz
    • +0, -3dB from 10Hz to 70kHz

CONTROL

• Remote Power Control: Yes
• Multi-Channel DB25 Cable: N/A

CONNECTIVITY

• Speaker Terminal Type: Solid Cinch™ Gold-Plated Speaker Terminals

GENERAL SPECIFICATIONS

• Circuit Configuration
  • Solid-State section: Quad Balanced
  • Vacuum Tube section: Unity Coupled
• Circuit Design: Solid-State and Vacuum Tube
• Output Type
  • Solid-State section: Autoformer™
  • Vacuum Tube section: Unity Coupled Output Transformer
• Meters: DualView™ Power Meter
• Meter Light Switch: Yes
• Balanced Input: 3 (1 Solid State, 1 Vacuum Tube, 1 Composite)
• Unit Dimensions (W x H x D): 17-17/32" (44.5 cm) x 13-3/8" (34 cm) x 29-17/32" (75 cm)
• Unit Weight: 180 lbs (81.6 kg)