MC451

The McIntosh MC451 is a 2-channel mono amplifier for bi-amping loudspeakers, combining a 150 Watt vacuum tube amplifier with a 300 Watt solid state amplifier in a conventional McIntosh form factor. Its size allows it to fit more easily into home audio systems, racks and furniture than the larger MC901.

The vacuum tube section powers the loudspeaker’s midrange and tweeter drivers, while the solid state section powers the woofers. Four KT88 output tubes sit beneath a removable wire cage, supported by two 12AT7 signal tubes and 1 12AX7A signal tube. McIntosh’s patented Unity Coupled Circuit output transformer allows the valve section to deliver its full 150 Watts into speakers with 2, 4 or 8 Ohm impedance.

McIntosh Autoformer^™ technology enables the 300 Watt solid state amplifier to deliver its full output into speakers with 2, 4 or 8 Ohm impedance. A large, quiet toroidal transformer supplies power to both amplifier sections so that neither draws power or performance from the other. Each section is engineered to amplify its intended frequency range, providing an integrated approach to bi-amping without separate amplifiers or an external crossover.

The internal adjustable crossover can be set to match the loudspeaker’s crossover point. Turn the CROSSOVER POINT knob on the rear panel to the required setting, sending frequencies below that point to the solid state amplifier and frequencies above it to the vacuum tube amplifier. Vacuum tube amplifier gain is adjustable from -6dB to +3dB. A direct feed can also be connected to each amplifier section, bypassing the internal crossover.

McIntosh MC451 has a DualView^™ Power Output Meter, with 2 traditional fast-responding mechanical meters arranged above and below each other in a single window. One displays the real-time power reading of the 150 Watt vacuum tube amplifier, while the other monitors the 300 Watt solid state amplifier. Each meter operates independently.

• Power Guard^® monitors and adjusts the input signal in the 300 Watt solid state amplifier section in real time. It makes subtle volume adjustments to help prevent harsh distortion and potentially damaging speaker clipping.
• Power Guard Screen Grid Sensor^® (SGS) monitors screen grid current in the KT88 output tubes. If the current becomes too high, the circuit dynamically attenuates the input signal in real time to keep the tubes operating at safe levels and help prevent premature failure.
• Sentry Monitor^™ monitors output current and switches the amplifier off if it exceeds safe limits.
• Power Control sends power on and off signals to other connected McIntosh components for system start-up and shutdown.
• Patented, gold-plated Solid Cinch^™ speaker binding posts attach speaker cables securely.
• McIntosh Monogrammed Heatsink^™ connects to high-current output transistors to cool the solid state amplifier section efficiently.
• Power Management System switches the unit off after a set period when no input signal has been detected.

The front panel uses a black glass faceplate with 3 clear windows for viewing the vacuum tubes and DualView meter. It also contains 2 rotary control knobs, an illuminated logo and lettering, and built-in aluminium handles. Glass inserts on the top panel carry block diagrams showing the circuitry and specifications. The components are housed in a polished stainless steel chassis with a mirror finish.

McIntosh MC451 can be used with preamplifiers, turntables, CD players, media streamers, loudspeakers and other specialist products to create a complete home audio system for bi-amping loudspeakers.