16
The Autoformer
creates an ideal
match between the
power amplifier
output stage and the
loudspeaker. Refer
to figure 16.
There is abso-
lutely no perfor-
mance limitation
with an Autoformer.
Its frequency re-
sponse exceeds that
of the output circuit
itself, and extends
well beyond the
audible range. Its
distortion level is
so low it is virtu-
ally impossible to
measure.
In the rare event of a power amplifier output circuit
failure, the McIntosh Autoformer provides absolute
protection from possible damage to your valuable
loudspeakers. The unequaled expertise of McIntosh
in the design and manufacturing of Autoformers is
legendary in the high fidelity industry. McIntosh engi-
neers know how to do it right.
Power Output Meter
The McIntosh MC302 has large Output Watt
Meters that respond 95% full scale to a single cycle
tone burst at 2kHz. Refer to figure 17. The Voltage
Output is electronically measured and fed to a special
circuit that accelerates the pointer movement in the
upward direction. Refer to figure 25 on the next page.
When the pointer
reaches its peak
it pauses only
long enough for
the human eye to
perceive its posi-
tion, then drops.
It is almost 10
times faster than
a professional
VU meter.
A front panel
switch is provided to change the meter to the Watts
Hold Mode of operation. This allows fast upward
movement of the pointer but greatly increases Hold
Time at the peak of its travel. The highest power out-
put of the source material is thus recorded.
Protection Circuits
The MC302 incorporates the McIntosh Sentry Moni-
tor Output Transistor Protection Circuit. Refer to
Figure 18. There is absolutely no compromise in sonic
performance with
this circuit, and it
ensures safe opera-
tion of the ampli-
fier under even
the most extreme
operating condi-
tions. The different
types of protection
circuits incorpo-
rated in the MC302
insure a long and safe operating life. This is just one
of the many characteristics of McIntosh Power Ampli-
fiers that make them world famous.
The MC302 also includes the unique patented
McIntosh Power Guard circuit. Power Guard elimi-
nates the possibility of ever overdriving the ampli-
fier into clipping. Refer to figures 19, 20 and 21. An
overdriven amplifier can produce both audible and
inaudible distortion
levels exceeding 40%.
The audible distortion is
unpleasant to hear, but
the inaudible ultrasonic
distortion is also undesir-
able, since it can damage
valuable loudspeaker
system tweeters. You
will never experience the
harsh and damaging dis-
tortion due to clipping.
The Power Guard
circuit is a waveform
comparator, monitoring
both the input and out-
put waveforms. Under
normal operating condi-
tions, there are no differ-
ences between the shape
of these waveforms. If
an amplifier channel is
overdriven, there will be
a difference between the
two signal waveforms.
When the difference
exceeds 0.3%, the Power
Guard activates the PG
light and a dynamic electronic attenuator at the ampli-
fier input reduces the input volume just enough to
prevent any further increase in distortion. The Power
Figure 20
Without Power Guard
Figure 19
Input Test Signal
(14kHz & 15kHz)
Figure 18
Normal Operating Area
Sentry Monitor
Safety Area
Output
Transistor
Failure
Technical Description, con’t
Figure 17
Figure 16
