McIntosh MC301 Owner's Manual page 16

Technical Description, con't
Power Output Meter
The McIntosh MC301 has a large Output Watt Me-
ter that responds 95% full scale to a single cycle tone
burst at 2kHz. Refer to figure 19.
Figure 19
Voltage output is electronically measured, multiplied
and fed to a special circuit that accelerates the pointer
movement in the upward direction. Refer to figure 14
on the previous 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 professional VU meter.
16
Protection Circuits
The MC301 incorporates the McIntosh Sentry Monitor
Output Transistor
Protection Circuit.
Refer to Figure 20.
There is absolutely
no compromise in
sonic performance
Normal Operating Area
with this circuit,
and it ensures safe
Sentry Monitor
operation of the
Safety Area
amplifier under
even the most
extreme operating
conditions. The different types of protection circuits
incorporated in the MC301 insure a long and safe
operating life. This is just one of the many character-
istics of McIntosh Power Amplifiers that make them
world famous.
The MC301 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 21, 22 and 23.
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 distortion due to clipping.
The Power Guard circuit is a waveform compara-
tor, monitoring both the
input and output wave-
forms. Under normal
operating conditions,
there are no differences
between the shape of
these waveforms. If the
amplifier is overdriven,
Output
there will be a differ-
Transistor
Failure
ence between the two
Figure 20 signal waveforms. When
the difference exceeds
0.3%, the Power Guard
activates the PG light
and a dynamic electronic attenuator at the amplifier
input reduces the input volume just enough to prevent
any further increase in
distortion. The Power
Guard circuit acts so fast
that there are absolutely
no audible side effects
Input Test Signal
and the sonic purity of
(14kHz & 15kHz)
the music reproduction is
perfectly preserved. The
MC301 Power Amplifier
with Power Guard is not
limited to just the rated
power output, but will
actually produce distor-
tion free output well above its rated power due to the
McIntosh philosophy of conservative design.
Figure 21
Without Power Guard
Figure 22
With Power Guard
Figure 23