McIntosh MC452 Owner's Manual page 16

Technical Description, con't
Power Output Meter
The McIntosh MC452 has large Output Watt Meter
that responds 95% full scale to a single cycle tone
burst at 2kHz. Refer to figure 17. Voltage and cur-
rent 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
professional 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.
Protection Circuits
The MC452 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 op-
eration of the amplifier under even the most extreme
operating conditions. The different types of protection
16
circuits incorpo-
rated in the MC452
insure a long and
safe operating life.
This is just one of
the many charac-
teristics of McIn-
tosh Power Ampli-
fiers that make
them world famous.
The MC452
also includes the
unique patented McIntosh Power Guard circuit. Power
Guard eliminates the possibility of ever overdriving
the amplifier into clip-
ping. Refer to figures
Figure 17
19, 20 and 21. An over-
driven 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 sys-
tem 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 waveforms.
Under normal operating conditions, there are no
differences between the shape of these waveforms. If
Normal Operating Area
Sentry Monitor Output
Safety Area Transistor
Failure
Figure 18
Input Test Signal
(14kHz & 15kHz)
Figure 19
an amplifier channel is
Without Power Guard
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 amplifier input
reduces the input volume
just enough to prevent
any further increase in
distortion. The Power
Guard circuit acts so fast
With Power Guard
that there are absolutely
no audible side effects
and the sonic purity of
the music reproduction is
perfectly preserved. The
MC452 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.
Power Supply Circuits
To compliment the design of the MC452 Power Am-
plifier Circuitry, there is a high current high voltage
power supply for both channels. Refer to figures 22
and 25. The very large Power Transfomer can supply
Figure 20
Figure 21