Mcintosh MC 2500, MC 2255, MC 2250, MC 2155, MC 2120, MC 502, C 33, C 29, C 27, C 504, MR 80, MR 78, MR 75, MX 117, MAC4100, MA6200, MQ107, MQ 104 catalog
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The World Wide Leader
In State Of The Art
High Fidelity Technology
Engineered and Manufactured
in the United States of America
Mclntosh Laboratory Inc.
2 Chambers Street
Binghamton, New York, 13903-9990
Phone 607-723-3512
YOU SHOULD OWN
McIntosh
BECAUSE
TABLE OF CONTENTS
Power Amplifiers:
MC 2500, MC 2255, MC 2250, MC 2155, MC 2120,
MC 502
2-16
PreAmplifiers:
C 33, C 29, C 27, C 504
14-24
Tuners:
MR 80, MR 78, MR 75 25-37
Tuner-Preamplifier:
MX 117 38-45
Receiver:
MAC4100 AM/FM Receiver 46-50
Preamplifier- Amplifier:
MA6200 51
Loudspeakers: 52-65
The Mclntosh Story 66-67
Equalizers:
MQ107, MQ 104 68
FM Guide. . . 69-76
• Mclntosh instruments are design-
ed and manufactured for long life.
• Mclntosh instruments have always
been designed for long life with low
maintenance costs and high quali-
ty performance. Mclntosh in-
struments have been and are the
LABORATORY STANDARD
for the world.
• Until 1949 the performance re-
quirements for a Mclntosh had
long been an engineering dream.
They became a reality with the in-
troduction of the first Mclntosh
amplifier. Through all these years
Mclntosh has produced instru-
ments that have exceptionally long
life. Clinics held ail over North
America have shown that most of
the Mclntosh instruments ever
manufactured still meet or exceed
their original exacting specifica-
tions.
• Used McIntosh instruments have
the highest resale value. Retailers
report that customers are constant-
ly searching for used Mclntosh in-
struments. A Mclntosh does not re-
main on the "Used" display long.
You'll get more when you trade-in
your Mclntosh assuring you of
maximum return on your invest-
ment,
• Mclntosh dedication, not only to
improvements, but also to fun-
damentals, has justified many
patents on basic circuit structures
as well as refinements.
• Doesn't it make good sense to deal
with a company that wants to do as
much for you as it possibly can?
1
THE NEW
MCINTOSH AMPLIFIERS
Mclntosh leadership in research and bipolar
epitaxial transistor technology has produced
startling new advances in safe, cool,
superior performance and protection.
Mclntosh engineering continues to advance
power amplifier technology and protected perfor-
mance. Experience and knowledge are the found-
ation on which the engineering superstructure is
built that supports the Mclntosh recognized reputa-
tion as Laboratory Standard for the world. A new
level of technology and a higher level of amplifier
performance is realized in the all new Mclntosh
Amplifiers.
LEADERSHIP
• Mclntosh life testing selects only components
that give the most trouble free performance. Add-
ed care in engineering, design and manufacturing
produces long product life at the peak of perfor-
mance.
LEADERSHIP
• Mclntosh POWER GUARD assures maximum am-
plifier power without clipping distortion.
LEADERSHIP
• Mclntosh engineers developed a unique output
circuit configuration that is temperature stable
and that delivers clean output power at any level
without a trace of crossover distortion.
LEADERSHIP
• Mclntosh Automatic System . Test provides
positive protection and extends the long trouble
free life of an amplifier. Each time an amplifier is
turned on, seven tests are completed that
measure and verify accurate performance.
LEADERSHIP
• Mclntosh Output Autotransformers deliver full
power output and multiple feedback loops assure
lowest distortion at all power levels and all
speaker impedances.
LEADERSHIP
• Mclntosh designed mute circuits give positive
protection from transients due to turn on, turn off
power supply voltage changes.
MC 2255 Shown in optional walnut veneer cabinet
2
YOU ARE PROTECTED FROM
LISTENING TO AMPLIFIER
PRODUCED DISTORTION
WITH MCINTOSH
POWER GUARD
Plus:
• Mclntosh Output Autotransformer delivers full
power output. Multiple feedback loops assure
lowest distortion at all power levels and all
speaker impedances
• Mclntosh engineers developed a unique output
stage circuit arrangement that is completely
temperature accurate, that delivers clean output
power at any level without crossover distortion
• Mclntosh life testing of components permits com-
ponent selection for trouble-free performance; ad-
ded care in production engineering and manufac-
turing results in long product life
• Mclntosh designed "turn-on/mute" circuits pro-
vide positive protection from "turn-on transients"
and other potentially damaging noises
• Mclntosh POWER GUARD assures maximum
amplifier power without clipping distortion
Higher power demands on amplifiers have
presented music listeners with a form of unpleas-
ntness in listening, amplifier overload (hard clipping)
that looks and acts like square waves. Clipping is
caused when the amplifier is asked to produce more
power output with low distortion than it can deliver.
Clipping of a complex wave form is largely compos-
ed of odd order harmonics and intermodulation pro-
ducts. High order odd harmonics and intermodula-
tion products are dissonant and are not musically
related to the signal being amplified. They are heard
as great and disappointing discordance and distor-
tion.
In most acoustical events we may listen to sur-
prisingly low average power output but the peak
power requirements can be very high. Consider
these graphs of the power demanded of an amplifier
reproducing the piano, the pipe organ, and the bass
saxophone. The charts show that the peak power de-
mand is almost 1000 times (30 dB) the average power
demand. Since it is necessary that these short inter-
val power spikes be reproduced with low distortion,
it means the average power output of the power
amplifier must be limited to 1/1000th of its capability
or the listener must accept the discordant distortion
of clipping.
Amplifiers when driven to clipping are capable of
delivering up to twice the heat load to the
loudspeaker. In addition, they can have more than
40% harmonic distortion. The extra heat energy con-
tent of the clipped signal will damage most
speakers. Mclntosh leadership in engineering has
developed a new circuit that...(1) dynamically
prevents power amplifiers from being overdriven in-
to hard clipping. ..(2) which reduces the heat
developed in the loudspeakers. ..(3) assures that the
amplifier will produce its maximum output without
increased distortion. That circuit we call "POWER
GUARD."
20 100 1K 10K
HERTZ
-30
0
30
PIANO
PIPE ORGAN
30
0
-30
20 100 1K 10K
HERTZ
BASS SAXOPHONE
30
0
-30
20 100 1K 10K
HERTZ
3
THE MCINTOSH POWER GUARD
The Power Guard waveform comparison circuit
detects minute amounts of waveform difference be-
tween the output signal and the input signal. A
sampling of the program material at the output of
the amplifier is constantly compared with the pro-
gram material at the amplifier input. Should the dif-
ferences reach 1%, Power Guard goes to work.
THE MCINTOSH POWER METERS
Mclntosh developed output monitoring meters
add to your operating flexibility. Ordinary meters are
incapable of indicating the short interval informa-
tion in a sound wave. The mass of the meter move-
ment is too great to respond to the instantaneous
changes in music program material. That short inter-
val information can have a duration as brief as one-
half of one thousandth of a second. Even should the
meter be capable of the high velocity movement the
human eye could not perceive the information.
Oscillogram of output waveform with and without Power Guard.
Input overdriven for each trace 20 dB.
In only a fraction of a millisecond Power Guard
dynamically reduces input level to prevent amplifier
overload yet permits the amplifier to deliver its ab-
solute maximum power output without extra distor-
tion. In addition, the output of the "waveform com-
parator" activates the front panel NORMAL and
LIMIT indicators.
The Power Guard circuit provides a precise visual
indication when the amplifier has reached full power
output. Any time that the input circuit is fed ex-
cessive amounts of signal causing waveform dif-
ferences through the amplifier of 0.5%, the output
mode indicators change from green NORMAL to red
LIMIT automatically and instantaneously. This warn-
ing persists long enough for positive visual indica-
tion of clipping for a pulse that is so infrequent or
short that it would be impossible to be seen even on
an oscilloscope. The indicators will illuminate on
clipping for a pulse as short in time as 100 microsec-
onds. You are always assured that the power of your
amplifier is as clean and distortion free as it can be.
Mclntosh engineering pursued both problems
electrically by developing new electronic circuits
that cause the meters to respond to short interval in-
formation with an accuracy of 98%! To permit the
eye to see such high speed motion the electronic cir-
cuits that drive the meter pointer are time stretched
so the meter pointer position can register in the per-
sistence of vision characteristics of the human eye.
The meters indicate directly in watts, or can be
made to hold the highest reading and continuously
update on higher power or can be switched to be
peak reading — peak locking decibel meters.
When used as a watt indicating meter all the infor-
mation is direct reading, without conversions or
complicated mathematics. In addition, as direct
reading meters they are calibrated in average watts
for a sine wave signal but respond to signal peaks.
The meters indicate direct power in watts. They
are calibrated in average watts for a sine wave
signal but respond to signal peaks. So, a 200
average watt indication also means 400 instan-
taneous peak watts. The meters are voltage ac-
tuated and indicate power accurately when the
amplifier is operated into rated output load im-
pedances.
Watts Hold, permits the meter to lock to and in-
dicate the highest power peak in a sequence of
peaks. The meter will be driven to maximum power
and electronically held there until a higher peak
passes through the amplifier. If no further peaks are
reached the meter needle will very slowly return to a
lower peak or to its rest position at a decay rate of 10
dB per minute.
4
The meters have extremely fast rise time, about
500 microseconds for 90% accuracy. A tone burst of
500 microseconds is almost inaudible even at full
power.
The meters are protected from damage in the
event of overloading in the wrong meter range.
AUTOMATIC TEST SYSTEM
The Automatic Test System provides positive pro-
tection and extends the long trouble free life of an
amplifier. Each time the amplifier is turned on an
Automatic Test System measures and verifies ac-
curate performance at seven critical points in the
amplifier's circuits. The Automatic Test System
verification assures operational readiness before
operation starts and limits any damage should there
be component malfunction. Each time a test is
verified an LED number indicator shows which test
is being performed. An adjustable "beep" tone can
be heard with each test.
If in the testing an unacceptable voltage is en-
countered, the LED numeric designation locks to
isolate the faulty circuit. Faulty circuit identification
permits the service technician more efficient repair.
Without the Mclntosh Automatic Test System at-
tempts to locate a fault by the probing and testing
needed, will often create additional problems by put-
ting undue mechanical and electrical stress on the
circuit components. The Automatic Test System pro-
tects your investment.
THE MCINTOSH OUTPUT CIRCUIT DESIGN
To achieve long trouble free life in an amplifier it
is essential to have cool operation. Cool operation
results from the careful design of the output circuit,
matching of the output circuit to the loudspeakers
with an autotransformer and a mechanical design
that permits the use of generous sized heat sinks
providing adequate ventilation without the use of
fans.
The bipolar eptaxial output transistors and the
Mclntosh output circuit allows the amplifier to
operate as cool as possible. When there is limited
program demand on the amplifier only the optimum
number of output devices operate. When there is no
signal no output device is conducting. Conservative
Mclntosh engineering keeps operating temperatures
low assuring long life.
The interleaved multifilar wound Mclntosh design-
ed autotransformer transfers all the power you paid
for to all impedance taps. You are not power penaliz-
ed for operating at an output impedance of less than
8 ohms. The Mclntosh autotransformer does its out-
standing job without adding phase shift, limiting fre-
quency response or power output. The distortion
through the autoformer is 0.003% at 20 Hz and
unmeasurable at higher frequencies. In short, the
Mclntosh autotransformer is the ideal answer to a
difficult problem.
Heat sinks must be large and they must have ade-
quate ventilation for effective cooling. For example
the MC 2255 has 1100 square inches (7.64 square
feet) of radiating surface. In addition, the chassis
has been designed to permit the maximum amount
of air to flow over the heat sinks to conduct away the
life limiting heat.
Mclntosh amplifiers provide the correct connec-
tion impedance to drive numbers of speakers simul-
taneously. For instance the 1 ohm output will drive
eight 8 ohm speakers and deliver full power without
overheating.
MC 2155 shown in optional walnut veneer cabinet.
5
test reports
"Reprinted with permission from the June 1982 issue of STEREO REVIEW magazine.