15
considerably from what
a loudspeaker requires.
In the case of more
than one loudspeaker
connected in parallel,
the load to the power
amplifier may drop
to two ohms or even
less. A power ampli-
fier connected to a
load that is lower than
optimum, causes more
output current to flow,
which results in extra
heat being generated in
the power output stage.
This increase in temperature will result in a reduced
life expectancy for the amplifier.
non-feedback designs. Refer to figure 15.
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 prod-
uct and large active region safe operating area. These
Power Transistors are the very latest in semiconductor
technology and incorporate a new design known as
ThermalTrak™. Refer to figure 13. This
allows for the instantaneous and accu-
rate monitoring of the Power Transistor
Temperature. The MC302 Power Output
Circuitry has a specially designed bias cir-
cuit to take full advantage of the Thermal-
Trak™ Power Transistors and thus precise-
ly 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 ab-
sorption film capacitors are used in all critical circuit
locations.
The output signals of the amplifier circuit is
coupled together in the unique McIntosh MC302
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 expertise
of McIntosh in the design and manufactur-
ing of autoformers is legendary in the high
fidelity industry.
The high efficiency circuit design of the
MC302 contributes to low operating tem-
peratures. More than 1400 square inches of
heat sink area keep the MC302 operating
safely with convection cooling. No fans are
needed. Refer to figure 14.
Autoformers
All solid state power amplifier output
circuits work best into what is called an
optimum load. This optimum load may vary
Technical Description
Figure 13
Figure 15
Block Diagram of the Power Amplifier
(one channel shown)
ThermalTrak
DC BIAS
OUTPUT
MUTE
THERMAL
SENSORS
BALANCED
AMP
POWER GUARD
ATTENUATOR
INPUT MODE
SWITCH
-
AMP
+
AMP
UNBALANCED
INPUT
BALANCED
INPUT
+
-
com
Figure 14
