McIntosh MC901 Hybrid Drive Dual Mono Amplifier
The McIntosh MC901 is a one-of-a-kind, 1-channel Hybrid Drive power amplifier created specifically for reference-level bi-amping. Each MC901 combines a 300-watt vacuum tube amplifier and a 600-watt solid state amplifier on one unified chassis, allowing the tube section to power a loudspeaker’s midrange and high-frequency drivers while the solid state section controls its woofers.
The MC901 is sold individually. One amplifier powers one compatible bi-amp-capable loudspeaker. A conventional stereo system requires two MC901 amplifiers.
Two Amplifiers Working as One
The MC901 is often described as a Dual Mono amplifier because it contains two fully developed amplification sections with separate power supplies and signal paths. Unlike a stereo amplifier, however, both sections are dedicated to a single loudspeaker:
- 300-watt vacuum tube section: Designed for the speaker’s midrange and high-frequency drivers.
- 600-watt solid state section: Designed for the power-hungry woofer section.
The vacuum tube amplifier uses eight KT88 output tubes, four 12AT7 tubes and two 12AX7A tubes. McIntosh’s Unity Coupled Circuit output transformer allows the tube section to deliver its full 300 watts into 2-, 4- or 8-ohm loads. The solid state section uses McIntosh Autoformer technology to provide its full 600 watts into 2, 4 or 8 ohms.
The two ratings are not combined into a conventional 900-watt full-range output. Each amplifier section powers a separate frequency range and must be connected to the appropriate terminals of a compatible bi-amp-capable loudspeaker.
Integrated Adjustable Crossover
Traditional bi-amping typically requires two separate amplifiers, an external crossover and careful level matching. The MC901 brings those functions together in one purpose-built chassis. Adjustable high-pass and low-pass filters are located on the top rear of the amplifier, making it possible to optimize the transition between the tube and solid state sections for the connected loudspeaker.
Relative gain for each amplifier section can be adjusted from -6dB to +3dB. Separate direct inputs also allow the internal filters to be bypassed when an external active crossover or loudspeaker-management system is being used.
Hybrid Drive Sound and Control
McIntosh Hybrid Drive technology is intended to combine the characteristics of vacuum tube amplification with the control and current delivery of a high-power solid state amplifier. The tube section is relieved of deep-bass reproduction and can concentrate on the midrange and treble, while the 600-watt solid state section supplies the damping and power required for demanding woofers.
Each section has its own discrete power supply, so neither amplifier draws operating reserves from the other. This arrangement allows both sections to perform as dedicated amplifiers rather than as two outputs sharing a compromised power supply.
DualView Power Output Meter
The MC901 introduced McIntosh’s DualView power-output meter. Two fast-responding mechanical meters are stacked in a single illuminated window:
- The upper meter displays the output of the 300-watt vacuum tube amplifier.
- The lower meter displays the output of the 600-watt solid state amplifier.
Both sections can therefore be monitored independently while retaining the signature blue McIntosh meter presentation.
McIntosh Protection Technologies
- Power Guard®: Monitors the solid state section and helps prevent harsh clipping and potential loudspeaker damage.
- Power Guard Screen Grid Sensor™: Monitors screen-grid current in the KT88 output tubes and dynamically reduces the input signal when necessary to help protect tube life.
- Sentry Monitor™: Protects the amplifier against unsafe output-current conditions.
- Quad Balanced solid state design: Helps cancel noise and distortion within the signal path.
- Power Control: Coordinates startup and shutdown with compatible McIntosh components.
- Power Management: Can switch the amplifier off after a selected period without an input signal.
Flexible Input Configuration
The MC901 provides composite inputs that feed both amplifier sections through the internal crossover, along with direct inputs for the vacuum tube and solid state sections. Balanced connections allow it to integrate with reference preamplifiers and active crossover systems while maintaining separate signal paths when required.
A natural system partner is the McIntosh C12000 Preamplifier, which provides balanced outputs and selectable tube or solid state operation for a complete reference-level McIntosh system.
MC901 vs. MC451
The McIntosh MC451 uses the same basic Hybrid Drive concept in a smaller and lighter design. The MC451 provides 150 watts of tube power and 300 watts of solid state power, while the MC901 doubles those ratings to 300 and 600 watts. The MC901 also uses a larger Quad Balanced solid state section and is intended for the most demanding loudspeakers, larger rooms and systems requiring substantial low-frequency control.
The MC451 is generally the more practical option where its lower output is sufficient. The MC901 is the statement choice for loudspeakers that can take advantage of its power, scale and independently optimized tube and solid state sections.
Installation and Loudspeaker Requirements
The MC901 should only be used with loudspeakers designed for bi-wiring or bi-amping, with electrically separate low-frequency and mid/high-frequency input terminals. Any factory jumpers between those terminal sections must be removed before connecting the separate MC901 outputs. The tube and solid state outputs must never be tied together.
At approximately 180 pounds and nearly 30 inches deep, each amplifier requires substantial equipment support, ventilation and access for the top-mounted crossover controls. A stereo pair weighs approximately 360 pounds before packaging, so floor loading, rack or platform capacity, delivery access and electrical requirements should be planned before installation.
McIntosh MC901 Specifications
| Amplifier Type | 1-channel Hybrid Drive dual-amplifier monoblock |
|---|---|
| Vacuum Tube Output | 300 watts into 2, 4 or 8 ohms |
| Solid State Output | 600 watts into 2, 4 or 8 ohms |
| Number of Channels | 1 |
| Vacuum Tubes | 8 KT88, 4 12AT7 and 2 12AX7A |
| Solid State Circuit Configuration | Quad Balanced |
| Vacuum Tube Circuit Configuration | Unity Coupled |
| Solid State Output Type | Autoformer™ |
| Vacuum Tube Output Type | Unity Coupled Circuit output transformer |
| Total Harmonic Distortion | Solid state: 0.005%; vacuum tube: 0.5% |
| Signal-to-Noise Ratio | Solid state: 122dB; vacuum tube: 112dB |
| Dynamic Headroom | Solid state: 2.5dB; vacuum tube: 1.2dB |
| Damping Factor | Solid state: greater than 40; vacuum tube: greater than 18 |
| Rated Power Band | 20Hz to 20kHz for both sections |
| Solid State Frequency Response | +0/-0.25dB from 20Hz to 20kHz; +0/-3dB from 10Hz to 100kHz |
| Vacuum Tube Frequency Response | +0/-0.5dB from 20Hz to 20kHz; +0/-3dB from 10Hz to 70kHz |
| Crossover | Adjustable high-pass and low-pass filters with direct-input bypass |
| Relative Level Adjustment | -6dB to +3dB for each amplifier section |
| Balanced Inputs | 3: solid state direct, vacuum tube direct and composite |
| Speaker Connections | McIntosh Solid Cinch™ binding posts for 2-, 4- and 8-ohm outputs |
| Meter | DualView™ Power Output Meter |
| Dimensions | 17-17/32 inches W x 13-3/8 inches H x 29-17/32 inches D |
| Weight | 180 lbs |
| Shipping Weight | 200 lbs |
| Warranty | 3-year limited warranty |
Frequently Asked Questions
Is the McIntosh MC901 sold as a pair?
No. The MC901 is sold individually. One unit powers one loudspeaker, so two MC901 amplifiers are required for a stereo pair.
Is the MC901 a 900-watt amplifier?
Not in the conventional sense. It contains a 300-watt tube amplifier and a separate 600-watt solid state amplifier. The two outputs feed different sections of a bi-amp-capable loudspeaker and are not combined into one full-range output.
Can the MC901 be used with any speaker?
No. The loudspeaker must provide separate, electrically isolated terminals for its low-frequency and mid/high-frequency sections. Loudspeaker crossover requirements and the recommended crossover point should be confirmed before installation.
Does the MC901 require an external crossover?
Usually not. The MC901 includes adjustable internal high-pass and low-pass filters. Direct inputs are available when an external crossover is preferred.
Can the tube and solid state sections be adjusted independently?
Yes. Their relative levels can be adjusted from -6dB to +3dB, and the crossover filters can be configured for the connected loudspeaker.
What is the main difference between the MC901 and MC451?
The MC901 provides twice the rated power of the MC451: 300 watts of tube power and 600 watts of solid state power versus 150 and 300 watts. It is also considerably larger and heavier.
Authorized McIntosh Dealer Support
Audio Exchange is an authorized McIntosh dealer in Richmond, Virginia. Our team can help determine loudspeaker compatibility, plan crossover settings, confirm preamplifier connections and address the delivery, support and electrical requirements of an MC901 stereo system. Explore additional options in our McIntosh Power Amplifiers collection.
