McIntosh MC275 Amplifier was produced by McIntosh from May, 1961 through July 1973.
The original Unity Coupled Circuit and McIntosh bifilar wound output transformer set a standard for
low distortion performance back in 1947. The output transformer had two primary
windings which are wound in a bifilar pattern. In this technique, both primaries are
wound side by side. Each turn of primary number one is next to the same turn of primary
number two. There is near complete magnetic coupling between the two wires. The magnetic
coupling is reinforced by the capacitance between the two wires.
In the McIntosh MC275 Unity Coupled Circuit, one of the bifilar primary windings is connected through
the power supply to the plate and cathode of one of the output tubes. The other bifilar winding
is connected to the other tube in the same manner. This unity coupled output virtually eliminates notch distortion.
The McIntosh MC275 used an advanced design of this technology by incorporating a trifilar wound
primary to improve the power bandwidth. The third winding is connected to the plates of the
cathode follower driver. Groups of interleaved primary and secondary windings improve coupling
and bandwidth of over 100,000 cycles is achieved.
* Tube Complement:
Voltage Amplifier - One 12AX7 (drives both amps)
Phase Inverter - Two 12AU7
Drive Amplifier - Two 12BH7
Cathode Follower Drive - Two 12AT7 or 12AZ7
Output - Four KT88 or 6550
* Selectable source input for Stereo, Twin-Amp or Mono operation.
* McIntosh MC275 Ouput is rated at 75 watts continuous per channel in Stereo or Twin configuration. 150 watts continuous mono.
* Harmonic Distortion is less than 0.5% at rated output or less for 20Hz through 20kHz.
Typical performance is 0.3% or less at 20Hz and 20kHz full power. Typical performance
in the mid frequencies is 0.1% or less at full power.
* Output barrier strips provide taps for speaker impedances of 4, 8 and 16 ohms stereo or 2, 4 and 8
ohms mono. The terminal strips may also be connected for a constant voltage output of 25 volts
in either stereo or mono, or for 70.7 volts in mono. The secondary of the McIntosh output transformer
may be operated either grounded or not grounded. If grounding is desirable, a wire may be connected
between chassis and common of either or both output termnal strips.
* An McIntosh MC275 octal socket marked line output has connections for 70.7volts, 115 volts, 230 volts or 600 ohms for stereo
300 ohms for mono operation. The 600 ohm winding and the 300 ohm winding are balanced to ground. Pin 1
of the octal socket is the center tap for these windings and is grounded.
McIntosh MC275 Gordon Gow Commemorative Edition
The McIntosh MC275 is a startling amplifier. From the moment I turned it on, I understood why it stayed in
production for a dozen years, and why mint-condition used MC275s often fetch up to eight times their
original purchase price This is a classic. Long after most other amplifiers, tube or solid-state, are forgotten,
the MC275 will still be a classic.
This is one of the most famous high-end amplifiers ever made. It's also, in my opinion,
one of the most beautiful amps ever made.
At $4000, the McIntosh MC275 isn't cheap. The price is high partly because of the US-made Richardson KT88 output tubes.
(The tubes are no longer made by Richardson in the US, but I understand that Richardson will be producing KT88s in France.)
The tubes cost McIntosh more than $115 a pop that's over $500 per McIntosh MC275 . Of course, McIntosh has to pass along the cost, but
I'm told they haven't marked them up. They make their margin on the amp itself, not the tubes.
What's really special about this amp is namely, the quality of dynamic drive. These amps
have an amazing amount of forward thrust. They punch out the music in a lively, exciting way lots of push/pull going on!
And not just on jazz or rock. Classical music, too, benefits from this added power or thrust. There's more
of a foundation on symphonic pieces. Cellos sound more exciting on string quartets. Even most
solid-state amps sound weak or wimpy compared to the McIntosh MC275 .
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