Technical Description - McIntosh MC611 Owner's Manual

Technical Description

McIntosh Laboratory, the company who introduced
the world's first amplifier that could be called "High
Fidelity", has done it again. The McIntosh engineering
staff has created a Power Amplifier without compro-
mise, using the most advanced McIntosh circuit design
concepts.
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The MC611 has a continuous average power output
rating of 600 watts and with a peak output current of
90 amperes; making this one of the most advanced
amplifiers available today. The distortion limits for the
MC611 are no more than 0.005% at rated power output
for all frequencies from 20Hz to 20,000Hz. Typical
Figure 13
performance at mid frequencies is
less than 0.002%. The true distor-
tion readings on the MC611 are
so low, it takes special measur-
ing techniques to make accurate
readings. The MC611 can deliver
the best possible performance
from any type of high quality
loudspeaker system. Refer to
figure 13.
Creating an amplifier with
this level of performance did not
come easily. Many months of de-
sign, testing and measuring were
required. Extensive controlled
listening tests, the ultimate form
of measuring, were made before
the final design was accepted.
Design Philosophy
The design philosophy incor-
porated in the MC611 involved
several different techniques, all
based on sound scientific logic.
Every stage of voltage or cur-
rent amplification must be as
linear as possible prior to the use
of negative feedback. McIntosh
engineers know how to properly
design negative feedback circuits so they contribute
to the extremely low distortion performance expected
from a McIntosh amplifier. The typical McIntosh
owner would never accept the approximately 100
times higher distortion of many non-feedback designs.
Double Balanced Push-Pull design is used from
input to output. Each half of the amplifier contains
complimentary balanced circuitry. The resulting Quad
Balanced configuration cancels even order distortion.
Refer to figure 16.
All transistors are selected to have nearly constant
current gain over the entire current range they must
cover. Output transistors in particular,
have matched uniform current gain, high
current bandwidth product and large
active region safe operating area. These
Power Transistors are the very latest in
semiconductor technology and incorpo-
rate a new design known as Thermal-
Trak™. Refer to figure 14. This allows for
the instantaneous and accurate monitor-
ing of the Power Transistor Temperature.
The MC611 Power Output Circuitry has a specially
designed bias circuit to take full advantage of the
ThermalTrak™ Power Transistors and thus precisely
controls the power amplifier operation over a wide
range of music conditions with the benefits of lower
distortion and cooler operation. Precision metal film
resistors and low dielectric absorption film capacitors
are used in all critical circuit locations.
The output signals of the two balanced circuits
are coupled together in the unique McIntosh MC611
Output Autoformer. It provides low distortion power
transfer at frequencies from below 20Hz to well
beyond 20,000Hz with optimum impedance points of
two ohms, four ohms and eight ohms. The unequaled
Figure 14