McIntosh MC901 Hybrid Drive MonoBlock Amplifier Pair - Pre-Loved

This is the first pre-owned pair of McIntosh MC901 we're offering for sale. 

These are pre-owned MC901's that come with a SkyFi 1-year warranty (no McIntosh warranty). 

Price listed is MSRP. Please call to order and discuss pricing.

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General:
These are stunning hybrid drive monoblock amplifiers from McIntosh. New today they're $22,000 each!

They deliver a whopping 300 watts of vacuum tube power PLUS another 600 watts of solid state. Best yet, since this unit utilizes McIntosh Autoformers it can deliver the same power to either a 2, 4, or 8 Ohm load. 

This pair are in great shape and only had one owner who took super care of them. You'd need to give them a close look to tell they were used.

In testing we decided to drive a pair of Sonus Faber floorstanding speakers. Everything sounded incredible  playing though these amplifiers and truly three-dimensional. The airplane crash from the first cut on Pink Floyd's "The Wall" actually rumbled our walls.

Included along with the MC901's are their original manuals, boxes, and tube cages.

We also have a pair of HRS E1 isolation bases designed for these amplifiers listed here.  

SkyFi Cosmetic Notes:
One heat sink is slightly discolored on the top edge, likely due to UV exposure over time. Light marks are present on some of the stainless surfaces. Overall, very good shape.

SkyFi Technical Notes:
All of the tubes were tested on our modern Amplitrex AT1000. The driver tubes all tested well. Two of the output tubes were slightly weaker than the rest. We replaced the suspect tubes with McIntosh labeled KT88's and selected four tightly matched quads, carefully placing them for optimal performance. Both the solid state and tube output sections tested to rated power with ease on both amplifiers.

From Mcintosh:
• Includes our Hybrid Drive™ technology that uses the best of vacuum tubes and solid state to produce the best sound performance
• The ultimate solution for bi-amping loudspeakers: 300 Watt vacuum tube amplifier and 600 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

McIntosh has been perfecting vacuum tube amplifiers since the 1940s and solid state amplifiers since the 1960s. Our amplifiers have been used at many historic events including presidential inaugurations and Woodstock, as well as in landmark sound systems like the Grateful Dead's Wall of Sound and Despacio. From that heritage comes a truly one-of-a-kind home audio amplifier only we could dream of, design and build as the ultimate solution for bi-amping loudspeakers: the McIntosh MC901 Dual Mono Amplifier.

The MC901 is a monoblock amplifier that drives a single speaker. But it is unlike any other monoblock amplifier. What makes the MC901 so unique is that it's two amplifiers combined into one. Adding to the uniqueness is that each amplifier is of differing design philosophies: the MC901 consists of a 300 Watt vacuum tube amplifier attached to a 600 Watt solid state amplifier on one unified chassis.

The MC901 includes our Hybrid Drive™ technology that uses the best of vacuum tubes and solid state to produce the best sound performance. The 300 Watt vacuum tube portion powers the speaker's mid and upper drivers via eight KT88 output tubes, plus four 12AT7 and two 12AX7A signal tubes; the solid state section delivers 600 Watts of dedicated power to the power hungry woofers. The 300 Watt vacuum tube amp in the MC901 uses our patented Unity Coupled Circuit output transformer – the same technology McIntosh was founded on in 1949 – to deliver its full 300 Watts into almost any speaker regardless if it has 2, 4 or 8 Ohm impedance. Similarly, the 600 Watt solid state amp delivers its full 600 Watts into a 2, 4 or 8 Ohm impedance speaker via our Autoformer™ technology.

Vacuum tubes do not perform at their best when they are amplifying lower frequencies that are not being used by the loudspeaker. With the MC901, the vacuum tube amp will not be burdened with low end reproduction as the solid state section will drive these frequencies. The two amplifier sections of the MC901 are designed to work together in a synergistic relationship and are specifically engineered to assure that each section only amplifies its intended frequencies. Each amplifier section has its own discrete power supply so neither siphons power or performance away from the other. All of this results in easy bi-amping with unparalleled performance and sound reproduction from your speakers.

Prior to the MC901, bi-amping a speaker required two separate amplifiers. It also required an external crossover, along with a lot of trial and error, to properly configure the two detached amplifiers so they worked together as best as possible. The MC901 solves this issue thanks to its internal, adjustable crossover with the controls easily accessible on the top of the unit. These adjustable crossover filters allow you to optimize the performance of both amplifier sections to your listening preferences. Relative gain levels for each amplifier section can be adjusted from -6dB to +3dB. A direct feed can also be connected to each amplifier section, thus bypassing the filters.
Like virtually all McIntosh amplifiers, the MC901 features an iconic "McIntosh Blue" Watt meter, which has come to be recognized around the world as a symbol of quality home audio. And just like the MC901 itself is a new design, so too is its meter with the introduction of our new DualView™ Power Output Meter. The DualView meter features two of our traditional, fast responding mechanical meters stacked above and below each other in a single meter window; one meter is dedicated to the 300 Watt vacuum tube amp and the other to the 600 Watt solid state amp. Each meter operates independently of the other and displays the real time power reading of each amplifier section.

While an entirely new design, the MC901 comes with the technology one would expect from a McIntosh amplifier:

• Power Guard® that monitors and adjusts the input signal in the 600 Watt solid state amplifier section in real time, then makes unobtrusive adjustments to prevent harsh sounding distortion and potential speaker damaging clipping.
• Power Guard Screen Grid Sensor™ (SGS). The 300 Watt vacuum tube amplifier section of the MC901 breaks new ground as it's our first amplifier to feature our new • 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.
• Quad Balanced design that cancels virtually all noise and distortion that may have crept into the audio signal.
• Power Control that can send power on/off signals to other connected McIntosh components for easy system power up and shutdown.
• Our patented, gold-plated Solid Cinch™ speaker binding posts that easily and securely attach the speaker cables.
• McIntosh Monogrammed Heatsinks™ that are connected to advanced high current output transistors efficiently cool the solid state amplifier section.
• Our Power Management System that will turn the entire unit off after a set amount of time when no input signal has been detected.

Although the MC901 may look different than any McIntosh product before it, a quick glance reveals signature McIntosh design cues. The top is highlighted by a series of diagrams printed on glass that outline the basic circuitry and specifications of the unit, along with a glass nameplate trimmed with a circular aluminum ring that's finished to match the front panel endcaps. The sides are adorned with vintage McIntosh-styled die cast aluminum name badges. Two classic McIntosh knobs are located on the front of the polished stainless steel chassis, and direct LED backlighting illuminates the DualView meter, McIntosh logo and the lettering on the black glass front panel.
The uncompromising level of fit and finish that is expected of a McIntosh product completes the MC901. It 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.

Brand Background:
McIntosh Laboratory is an American manufacturer of handcrafted high-end audio equipment based in Binghamton, New York. The company was founded in 1949 by Frank McIntosh. The company designs and produces audio amplifiers, stereo tuners and other consumer electronics products.

Ownership:
Single Owner

Connections:
RCA, XLR, 5 Way Speaker Binding Posts, IEC Power, Power Control

General Sound:
Big beautiful musical sound with little fatigue.

Cosmetic Condition:
8/10 = Very Good. Excellent front faceplate, one minor flaw on chassis side or top. See our detailed rating description here.

Working Condition:
Working perfectly and tested in our lab and listening room.

Included:
Unit, Box, Manual

Packing:
Original Manufacturers Packing

Original MSRP:
$44,000.00

Specs:
Power Output per Channel
Solid State section: 600 Watts @ 2, 4 or 8 Ohms
Vacuum Tube section: 300 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: 122dB
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

GENERAL SPECIFICATIONS
Circuit Configuration
Solid State section: Quad Balanced
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
3 (1 Solid State, 1 Vacuum Tube, 1 Composite)

Front Panel
Glass

Illumination
Direct LED

Chassis Style
Polished stainless steel & black painted steel

Dimensions - Each MC901:
17-17/32" (44.5cm) x 13-3/8" (34cm) x 29-17/32" (75cm)

Weight - Each MC901:
180 lbs.

Recommended Cables:
Kimber Kable - RCA Interconnects - Better

Kimber Kable - RCA Interconnects - Best

Kimber Kable - BALANCED XLR Connectors - Better

Kimber Kable - BALANCED XLR Connectors - Best

Kimber Kable - Speaker Cables - Better

Kimber Kable - Power Cords - Better

Kimber Kable - Power Cords - Best

Testing Process:
We start with a visual inspection of all internal components to make sure that there are no signs of heat stress or damage. Capacitors are checked for telltale signs of predictive failure including bulging, shrunken wrappers, or physical leakage. We also inspect resistors and other passive components for signs of overheating. If tube arcing has occurred in the past we can usually spot discoloration on the output tube sockets. On vintage units we often spot check select capacitors for value and ESR.

If the amplifier passes visual inspection, we move on to a full test of all of the tubes. We use a modern Amplitrex AT-1000 Professional Tube Tester which is capable of testing both emission and Gm with a high degree of accuracy.

We document the results of each tube and replace any weak or suspect tubes before proceeding.

When we power on tube amplifiers for the first time we usually use a variac and current limited AC supply and slowly raise the voltage up to nominal mains level while monitoring plate, screen, filament, and negative bias supply voltages where applicable.

If everything is in order we feed a low level test signal into the amplifier’s input and monitor its output on an oscilloscope across an 8 ohm dummy load. At this point we are just looking to verify basic function and confirm that the output transformers are not damaged.

Once we have verified that the amplifier is safe to operate, we connected it to full mains power. For fixed bias amps we set the bias to manufacturer spec. For cathode biased amps we monitor the plate to cathode voltage to determine if the output tubes are operating in a safe range. Once the output section is verified we move onto bench evaluation.

We start by feeding the input of the amplifier with a low level 1 KHz test signal, slowly increasing its amplitude while monitoring the amplifier’s output on an oscilloscope for signs of noise, clipping, distortion, or improper channel balance. We continue increasing the signal level until the amplifier reaches clipping. At this point we take an output power measurement and compare it to the spec sheet of the amplifier to verify proper performance.

We finish off the bench evaluation with a 1 KHz square wave check and a 20 Hz to 20 KHz sine sweep to assess the amplifier’s frequency response characteristics. This battery of tests will usually reveal if the amplifier has any issues that need further attention.

Before the device leaves the bench we perform a listening test with actual music using a variety of preferred test tracks. Our benches are outfitted with familiar monitor speakers which help us identify inconsistencies that will not always show up on our test gear. The main things that we are listening for are hum or noise with no signal present, proper center image, clicks, pops, or any other obvious undesirable audio characteristics.

If the unit passes all of these tests it is moved to our long term testing rig where we simulate real word operating conditions for 6-8 hours minimum.

For tube amps we like to run this test at least twice.

This allows us to monitor the unit for signs of thermal runaway or intermittent issues that only crop up when it has fully come up to temperature. We find this step to be essential, especially for vintage units.