McIntosh MC451 Dual Mono Amplifier

  • Includes Hybrid Drive™ technology that uses the best of vacuum tubes and solid state to produce the best sound performance
  • Designed with bi-amping loudspeakers in mind
  • 150 Watt vacuum tube amplifier and 300 Watt solid state amplifier on one chassis
  • Vacuum tube section powers mid and upper drivers
  • Solid state section drives power hungry woofers
  • DualView™ Power Output Meter

The MC451 Dual Mono Amplifier joins the MC901 in offering the ultimate solution to bi-amping a loudspeaker. Like the MC901, the MC451 uses Hybrid Drive™ technology that combines a separate vacuum tube and solid state amplifier onto one single chassis to produce the best possible sound performance from a bi-ampable speaker. Unlike the larger MC901, the MC451 has a more conventional McIntosh form factor and size, allowing it to fit into home audio systems, racks, and furniture more easily. Adding a pair of MC451s to your stereo system will allow your prized speakers to perform like never before.


The MC451 is comprised of a 150 Watt vacuum tube amplifier and a 300 Watt solid state amplifier, which is more than enough power to drive virtually all speakers.

The vacuum tube section drives the speaker's midranges and tweeters, while the solid state section drives the woofers. The 150 Watt vacuum tube amplifier is powered by four KT88 output tubes which are located under a removable wire cage, plus two 12AT7 and one 12AX7A signal tubes; it uses McIntosh's patented Unity Coupled Circuit output transformer to deliver its full 150 Watts into almost any speaker regardless if it has 2, 4 or 8 Ohm impedance.

Similarly, the 300 Watt solid state amplifier delivers its full 300 Watts into a 2, 4 or 8 Ohm impedance speaker via Autoformer™ technology.

The two amplifiers in the MC451 are designed to work together in a synergistic relationship and are specifically engineered to assure that each only amplifies its intended frequencies. The large but quiet toroidal transformer generates enough power so that neither amplifier robs power or performance from the other. All of this results in easy bi-amping with unparalleled performance and sound reproduction from your speakers.

Bi-amping your speakers with the MC451 is easy. No longer do you need fiddle with two separate amplifiers, an external crossover, and a lot of trial and error to properly configure the two separate amplifiers with often times only so-so results. The MC451 solves these hassles thanks to its internal, adjustable crossover. The MC451’s crossover tailors the output frequency range of each amplifier section to the attached loudspeaker. Simply set the CROSSOVER POINT knob on the back of the MC451 to the loudspeaker’s crossover point, then frequencies below the crossover point will be sent to the solid state amplifier and frequencies above it will be sent to the vacuum tube amplifier.

This adjustable crossover allows you to optimize the performance of both amplifier sections to your speaker's specifications and to your listening preferences. Gain levels for the vacuum tube amplifier can be adjusted from -6dB to +3dB. A direct feed can also be connected to each amplifier section, thus bypassing the internal crossover.

The MC451 features DualView™ Power Output Meter. The DualView meter features two of McIntosh's traditional, fast responding mechanical meters stacked above and below each other in a single meter window; one meter is dedicated to the 150 Watt vacuum tube amp and the other to the 300 Watt solid state amp. Each meter operates independently of the other and displays the real time power reading of each amplifier section.

In addition to everything already mentioned, the MC451 comes with a multitude of other McIntosh amplifier the technologies:

  • Power Guard® that monitors and adjusts the input signal in the 300 Watt solid state amplifier section in real time, then makes inconspicuous volume adjustments to prevent harsh sounding distortion and potential speaker damaging clipping.
  • Power Guard Screen Grid Sensor® (SGS). The 150 Watt vacuum tube amplifier section features 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.
  • Power Control that can send power on/off signals to other connected McIntosh components for easy system power up and shutdown.
  • McIntosh's patented, gold-plated Solid Cinch™ speaker binding posts that easily and securely attach the speaker cables.
  • A McIntosh Monogrammed Heatsink™ that is connected to advanced high current output transistors to efficiently cool the solid state amplifier section.
  • The Power Management System that will turn the entire unit off after a set amount of time when no input signal has been detected.

The uncompromising fit and finish of the MC451 is highlighted by familiar McIntosh design cues. The front features a signature black glass faceplate with three clear windows that allow viewing of the vacuum tubes, the DualView meter, two rotary control knobs, an illuminated logo and lettering, and built-in aluminum handles. The top is highlighted by a series of block diagrams printed on glass inserts outlining the circuitry and specifications of the unit. All of this sits atop of stainless steel chassis that's been polished to a pristine mirror finish.

The MC451 amplifier can be combined with a variety of preamplifiers, turntables, CD players, media streamers, speakers, and other specialty products to form a complete home audio system designed for bi-amping loudspeakers.


  • Power Output per Channel: Solid State section: 300 Watts @ 2, 4 or 8 Ohms, Vacuum Tube section: 150 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: 118dB, 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

General Specifications

  • Circuit Configuration: Solid State section: Push-Pull Complementary, 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: 2 (1 Solid State or Mono, 1 Vacuum Tube)
  • Front Panel: Glass
  • Illumination: Direct LED
  • Chassis Style: Polished stainless steel & black painted steel
  • Dimensions (W x H x D): 17-7/8" (45.4cm) x 11-13/16" (30cm) x 21-1/2" (54.6cm)
  • Weight: 133 lbs (60.3 kg), Shipping Weight: 159 lbs (72.1 kg)
In stock! Usually ships within 24 hours.
Availability: This product is available for purchase in-store only. Contact us for more information.