16
the harsh and damaging
distortion due to clipping.
The Power Guard
circuit is a waveform
comparator, monitoring
both the input and output
waveforms. Under normal
operating conditions,
there are no differences
between the shape of
these waveforms. If the
amplifier is overdriven,
there will be a difference
between the two signal
waveforms. When the
difference exceeds 0.3%,
the Power Guard acti-
vates the PG light and
a dynamic electronic
attenuator at the ampli-
fier input reduces the
input volume just enough
to prevent any further in-
crease in distortion. The
Power Guard circuit acts
so fast that there are ab-
solutely no audible side
effects and the sonic purity of the music reproduction
is perfectly preserved. The MC462 Power Ampli-
fier with Power Guard is not limited to just the rated
power output, but will actually produce distortion free
output well above its rated power due to the McIntosh
philosophy of conservative design.
Protection Circuits
The MC462 incorporates the McIntosh Sentry Moni-
tor Output Tran-
sistor Protection
Circuit. Refer to
Figure 19. There is
absolutely no com-
promise in sonic
performance with
this circuit, and it
ensures safe opera-
tion of the ampli-
fier under even
the most extreme
operating conditions. The different types of protection
circuits incorporated in the MC462 insure a long and
safe operating life. This is just one of the many char-
acteristics of McIntosh Power Amplifiers that make
them world famous.
The MC462 also includes the unique patented
McIntosh Power Guard circuit. Power Guard elimi-
nates the possibility of ever overdriving the amplifier
into clipping. Refer to
figures 20, 21 and 22.
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
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 engineers know how
to do it right.
Power Output Meter
The McIntosh MC462 has large Output Watt Me-
ters that respond
95% full scale to
a single cycle tone
burst at 2kHz.
Refer to figure
18. Voltage and
current outputs
are electronically
measured, multi-
plied 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 position,
then drops. It is almost 10 times faster than a profes-
sional VU meter.
A front panel switch is provided to change the
meter to the Watts Hold Mode of operation. This al-
lows fast upward movement of the pointer but greatly
increases Hold Time at the peak of its travel. The
highest power output of the source material is thus
recorded.
Figure 21
Without Power Guard
Figure 20
Input Test Signal
(14kHz & 15kHz)
Figure 22
With Power Guard
Figure 19
Normal Operating Area
Sentry Monitor
Safety Area
Output
Transistor
Failure
Technical Description, con’t
Figure 18
