MC901 Monoblocks

The McIntosh MC901 is a dual mono monoblock amplifier for bi-amping loudspeakers, with 300 Watts of vacuum tube amplification and 600 Watts of solid state amplification combined on a single chassis. McIntosh has developed vacuum tube amplifiers since the 1940s and solid state amplifiers since the 1960s, with its equipment used at presidential inaugurations and Woodstock, as well as in the Grateful Dead's Wall of Sound and Despacio sound systems.

Each MC901 drives one speaker while assigning different frequency ranges to its 2 amplifier sections. The 300 Watt vacuum tube section powers the midrange and upper drivers through 8 KT88 output tubes, 4 12AT7 signal tubes and 2 12AX7A signal tubes. The 600 Watt solid state section provides dedicated power for the loudspeaker's power-hungry woofers.

McIntosh's patented Unity Coupled Circuit output transformer, the technology on which the company was founded in 1949, enables the vacuum tube amplifier to deliver its full 300 Watts into speakers with 2, 4 or 8 Ohm impedance. The solid state amplifier uses McIntosh Autoformer technology to deliver its full 600 Watts into a 2, 4 or 8 Ohm impedance speaker.

Vacuum tubes are not suited to amplifying lower frequencies that the loudspeaker does not use. In the MC901, those low frequencies are handled by the solid state section, leaving the vacuum tube amplifier to power the mid and upper drivers.

The 2 amplifier sections are engineered to work together, with each one amplifying only its intended frequencies. Each has a separate discrete power supply, so neither section draws power or performance from the other. This arrangement provides straightforward bi-amping from the single MC901 chassis.