McIntosh MC 7270, Owner'S Manual

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The Mclntosh MC 7270 is the first and only amplifier
specially designed to fulfill Digital Dynamic Range
demands. It outperforms all others when listening to
sound derived from digitally recorded tapes, records and
compact discs. The MC 7270 has been designed to per-
form flawlessly because of this capacity for overload: 10
decibels of overstress at less than an average of 0.3% of
distortion! Mclntosh amplifiers with POWER GUARD are
the only amplifiers which can tolerate 10 decibels of
dynamic overload, without severe distortion breakup.
The noise level of digitally recorded sound is 30
decibels below that of conventional analog recordings.
Thirty decibels reduction of noise level means that the
digital disc noise power is 1000 times less than that on
the best analog records. The compact disc is capable of
real life dynamic range while noise generated from com-
pact discs is inaudible. With the noise restraint removed it
is both easier and dramatically more enjoyable to listen to
music at much louder levels. To fully enjoy this new
capability your amplifier must be able to receive three to
ten decibels of over stress from music, and it must do this
without severely distorting the sound!
For an amplifier to handle a three-decibel overload, it
must have a full time capacity of twice its full power. An
over stress demand of 10 decibels is a demand for 10
times the full power capacity of an amplifier. To provide
2500 watts of overload for a 250 watt amplifier is expen-
sive both in the amplifier and in the loudspeaker system
as well. This is the real world of Digital Dynamics Range
demand. How to achieve the performance demanded,
which often lasts from minutes to only a few thousandths
of a second, and to achieve the goal economically, is a
real achievement. In each Mclntosh MC 7270, there is a
unique, patented*, digital sonic overload corrector which
prevents the amplifier from exceeding an average of 0.3%
distortion for overload stresses up to 10 decibels!
Mclntosh has developed a new method of measuring
amplifiers which shows this capability very dramatically.
This is a test of the Spectral Fidelity of an amplifier under
stress.
SIMULATING COMPLEX CRESCENDO DEMANDS
Two tones, 14 kHz and 15 kHz, are fed to the input of
the amplifier under test. The output of the amplifier is fed
to a resistive dummy load across which is an A.C.
voltmeter, (to allow computation of the amplifier's output
power), and to a spectrum analyzer which displays the
magnitude and frequencies of signals at the amplifier out-
put.
Ideally, only the two test tones should be reproduced at
the amplifier output. Some amplifiers generate a broad in-
termodulation spectrum of tones corresponding to the
sum and difference of the test tones. These spurious
tones are called Intermodulation Distortion.
All amplifiers (Mclntosh amplifiers with Power Guard are
the only exception), produce such a spectrum when they
are driven beyond their output capacity. They produce In-
termodulation and Harmonic Distortion, the severity of
which depends on the amount of overdrive and the
design of the amplifier. Distortion of 30% or greater is not
uncommon. Most of the spurious frequency components
are at high frequencies and can easily destroy the tweeter
sections of loudspeakers, while severely distorting the
sound.
*U.S. Patent #4048573
INTRODUCTION 3