15
The output signal of the amplifier circuit is coupled
into the unique McIntosh MC152 Output Autoformer.
It provides low distortion power transfer at frequen-
cies 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 manufacturing of autoformers is leg-
endary in the high fidelity industry. Refer to figure 17.
The Autoformer
creates an ideal match
between the power am-
plifier output stage and
the loudspeaker. Refer to
figure 18.
There is absolutely no
performance limitation
with an Autoformer. Its
frequency response ex-
ceeds that of the output
circuit itself, and extends
well beyond the audible
range. Its distortion level
is so low it is virtually
impossible to measure.
The high efficiency circuit design of the MC152
contributes to low operating temperatures. More than
800 square inches of heat sink area keep the MC152
operating safely with convection cooling. No fans are
needed.
Autoformers
All solid state power amplifier output circuits work
best into what is called an optimum load. This op-
timum load may vary 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 amplifier 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 out-
put stage. This increase in temperature will result in a
reduced life expectancy for the amplifier.
Technical Description
Figure 18
Block Diagram of the Power Amplifier
(one channel shown)
Figure 15
ThermalTrak
DC BIAS
OUTPUT
MUTE
THERMAL
SENSORS
BALANCED
AMP
POWER GUARD
ATTENUATOR
INPUT MODE
SWITCH
-
AMP
+
AMP
UNBALANCED
INPUT
BALANCED
INPUT
+
-
com
Figure 17
