McIntosh MC901 Dual Mono Amplifier

The Ultimate McIntosh Approach to Bi-Amping

The McIntosh MC901 Dual Mono Amplifier is one of the most ambitious amplifiers McIntosh has ever created. It combines two completely different amplifier technologies on a single chassis: a 300-watt vacuum tube amplifier and a 600-watt solid-state amplifier, engineered specifically to bi-amp one loudspeaker.

The concept draws on both sides of McIntosh's history—vacuum tube amplification dating to the company's earliest years and decades of high-power solid-state amplifier development.

For a stereo system, two MC901s are required, with each amplifier dedicated to one bi-ampable loudspeaker.

300 Watts of Tubes + 600 Watts of Solid-State Power

McIntosh calls the architecture Hybrid Drive, but unlike a conventional hybrid amplifier, the tube and solid-state sections aren't simply different stages of the same amplifier.

They are two separate power amplifiers working together.

The 300-watt vacuum tube section is intended to drive the midrange and high-frequency section of the speaker. It uses eight KT88 output tubes along with four 12AT7 and two 12AX7A signal tubes.

The 600-watt solid-state section handles the power-hungry woofers, where tremendous output and control are particularly valuable.

This division of labor lets each amplifier technology concentrate on the frequency range it is intended to reproduce.

Full Power Into 2, 4 or 8 Ohms

Both halves of the MC901 incorporate signature McIntosh output technology.

The tube section uses the patented Unity Coupled Circuit output transformer, allowing it to deliver its full 300 watts into 2, 4, or 8 Ohms.

The solid-state amplifier uses a McIntosh Autoformer to provide its full 600 watts into 2, 4, or 8 Ohms.

That gives the MC901 tremendous flexibility when matching it to compatible bi-ampable loudspeakers.

A Smarter Way to Bi-Amp

The real achievement of the MC901 isn't simply putting two powerful amplifiers into one chassis. It's getting them to work together correctly.

In a traditional bi-amped system, two separate amplifiers may require an external crossover, gain matching, additional cables, and considerable experimentation.

The MC901 integrates an adjustable crossover network directly into the amplifier.

Controls located on top of the chassis allow the frequency ranges sent to the tube and solid-state sections to be tailored to the connected speaker. Relative gain for each amplifier can also be adjusted from -6dB to +3dB, allowing the two sections to be properly balanced.

For more specialized installations, each amplifier section can receive a direct signal that bypasses the internal filters.

Separate Power Supplies

The tube and solid-state amplifiers don't just have separate circuitry—they also have independent power supplies.

That's important in an amplifier capable of simultaneously producing 300 watts from its tube section and 600 watts from its solid-state section.

Heavy bass demands placed on the solid-state amplifier don't have to steal power reserves from the tube amplifier responsible for the midrange and high frequencies.

The MC901 is therefore better thought of as two purpose-built amplifiers sharing one extraordinary chassis rather than one amplifier divided into two sections.

DualView Power Output Meter

A conventional McIntosh Watt meter wouldn't tell the whole story here, so McIntosh developed the DualView Power Output Meter.

Two fast-responding mechanical meters are stacked within a single window.

One displays the real-time output of the 300-watt vacuum tube amplifier, while the other monitors the 600-watt solid-state amplifier.

The two meters operate independently, providing a visual representation of how power is being delivered to the different sections of the loudspeaker.

Engineering Made Visible

The MC901 doesn't look like a conventional McIntosh monoblock—and that's appropriate considering what is happening inside it.

Glass panels across the top display diagrams outlining the amplifier's circuitry and operation. Vintage-style die-cast McIntosh badges appear on the sides, while the polished stainless steel chassis, aluminum detailing, black-glass front panel, illuminated logo, and traditional control knobs maintain a clear connection to McIntosh design.

Direct LED illumination brings the DualView meter and front-panel lettering to life.

It's an amplifier designed to make its engineering part of the experience.

The Grid's Take on the McIntosh MC901

The MC901 is what happens when McIntosh takes the idea behind the MC451 and removes almost every practical restraint.

Instead of 150 watts of tube power and 300 watts of solid-state amplification, the MC901 provides 300 watts from its tube section and a massive 600 watts from its solid-state section—for each speaker.

But the numbers aren't really the most interesting part.

The MC901 solves one of the fundamental challenges of a serious bi-amped system: getting two very different amplifiers to operate together as a cohesive whole. McIntosh integrates the amplification, crossover, gain adjustment, impedance matching, and independent power supplies into a single purpose-built component.

For the right bi-ampable reference loudspeaker, a pair of MC901s creates an extraordinary configuration: tubes dedicated to the midrange and high frequencies, massive solid-state power controlling the woofers, and both optimized specifically for their respective jobs.

This isn't an amplifier we'd recommend simply because someone wants more power. The MC901 makes sense when the loudspeaker and the entire system are capable of taking advantage of what its architecture can do.

At The Grid HiFi & Home Theater, we can help determine whether your loudspeakers are appropriate for the MC901 and properly configure a complete system around a matched pair.