Page 1
McINTOSH QUALITY BEGINS WITH
CAREFUL DESIGN FOR COOL OPERATION
To achieve long trouble-free life in an amplifier it is
essential to have cool operation. As little as one de-
gree (centigrade) rise in temperature can reduce
the operating life of the amplifier 10%. Mclntosh
has extended the life of its amplifiers by engineer-
ing for cool operation. Long life of a Mclntosh is not
just
a
claim.
More
than
80% of the
Mclntosh ampli-
fiers produced since 1949 are still in service today.
Mclntosh cool operation requires a combination of
careful design of the output circuit, containing the
output circuit in a mechanical housing that per-
mits the use of generous sized heat sinks to provide
great heat dissipation capability along with chassis
construction that permits adequate ventilation,
then correctly matching the cool operating output
circuit to the loudspeakers with a Mclntosh de-
signed and manufactured auto-transformer.
The Mclntosh output circuit uses bipolar epitaxial
output transistors in a cleverly inventive design
that keeps the circuit components cool, extending
the long trouble-free life of the components. The
circuit has the ability to recognize the power de-
mands of the program material and then to acti-
vate only as much of the output circuit as is needed
to satisfy that demand. AH this occurs without the
crossover distortion found in conventional solid
state output circuits. (The amplifier circuit is a pa-
tented Mclntosh design U.S. patent #3526847.)
The Mclntosh output stages are mounted on heat
sinks that have maximum surface area of cooling
capability, the largest for equivalent power in the
industry. The super sized heat sinks are placed in
an air tunnel chassis design that occupies the en-
tire space from the bottom of the amplifier to the
top. Cooling air, flowing through the air tunnel,
easily dissipates any life limiting heat generated.
Page 2
VERSATILE MclNTOSH POWER
AMPLIFIERS DELIVER FULL POWER-
ALWAYS
The superior Mclntosh output circuit demands a
superior method of coupling the amplifier output
to the loudspeaker load. The Mclntosh designed
and manufactured autotransformer is a silent giant
that insures better performance and protection
and superior interaction between amplifier and
speaker. Its use provides many unseen benefits.
The autotransformer interconnection insures com-
plete stability of the amplifier. Other amplifier cir-
cuits need additional component considerations to
prevent instability with its subsequent threat to the
life and performance of the amplifier. It is the ideal
method of matching the output circuit to the loud-
speakers. Transistors, used in amplifier output cir-
cuits, are designed to work into an optimum low
impedance load. Frequently amplifier performance
will
be
compromised
by
speaker
impedance
varia-
tions with frequency or by the use of multiple
speakers which modify the impedance as seen by
the output of the amplifier. Without the Mclntosh
autotransformer, variables, such as these, can
cause restricted performance, output transistor
heating and then circuit failure.
A second benefit of the Mclntosh autotransformer
is the protection provided in the event of a failure in
the output circuit. Should any direct current com-
ponent appear at the output, the autotransformer
will
conduct
the
speaker
damaging
DC
directly
to
ground. Your expensive loudspeakers are protec-
ted from this potentially damaging circumstance.
Here's a third benefit of the Mclntosh autotrans-
former. It not only provides the output transistors
an ideal load and is the path that conducts any DC
away from the loudspeaker, it also contributes a
flexibility in loudspeaker connecting capability not
otherwise possible. For safe operation ordinary am-
plifier output circuits are usually restricted to oper-
ate into 4 or 8 ohms. In stereo, the Mclntosh auto-
transformer perfectly matches the output circuit to
1, 2, 4 or 8 ohms. In mono, (Mclntosh stereo ampli-
fiers can be interconnected for mono and deliver
twice the power) the autotransformers provide
matching ½,1, 2, 4, 8 or 16 ohms. In addition, in
either stereo or mono, the autotransformer pro-
vides a 25 volt output that may be used to feed
multiple loudspeakers for background music and
the like. Truly, the Mclntosh autotransformer is an
engineering marvel that enhances amplifier per-
formance without any technical or performance
drawbacks.
THE MclNTOSH (EXCLUSIVE) POWER
GUARD MUSIC PROTECTION CIRCUIT
Improved recordings and recording techniques
have imposed higher power demands on today's
amplifiers. Poorly designed amplifiers, of which
there are many, can present music listeners with a
form of harsh unpleasant distortion due to ampli-
fier overload (hard clipping). Clipping, which looks
and acts like non musical square waves, is caused
when the amplifier is asked to produce more power
output with low distortion than it is capable of or
designed to deliver. Amplifiers, when driven to clip-
ping, can deliver up to 4O% harmonic distortion.
Distortion decreases the pleasure and enjoyment of
listening. This form of distortion (clipped signal)
also
produces extra
heat
energy
which
will
damage
most speakers. Mclntosh leadership in engineering
has developed the Power Guard circuit which -
(1) dynamically prevents power amplifiers from be-
ing overdriven into hard clipping-(2) assures that
the amplifier will produce its maximum output
without increased distortion -(3) protects your
speaker from excessive heating. Power Guard is a
patented Mclntosh design (U.S. patent #4048573).
