McIntosh MC1.2KW - Manual (Page 17)

17
Technical Description, con’t
audible and inaudible distor-
tion levels exceeding 40%.
The audible distortion is
unpleasant to hear, but the
inaudible ultrasonic distortion
is also undesirable, 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 comparator, moni-
toring both the input and out-
put waveforms. Under normal
operating conditions, there
are no differences 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
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 and the sonic
purity of the music reproduction is perfectly preserved.
The MC1.2KW Power Amplifier 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.
Power Supply Circuits
To compliment the fully balanced design of the MC1.2KW
there are two high voltage power supplies; one for each
of the two
amplifier
circuits,
allowing
each ampli-
fier cir-
cuit to be
optimized
using its
own power
supply.
Refer to
figure 20.
High power
amplifiers draw high current from the AC power line. The
very large Power Transfomer, has toroidal windings on a
toroidal core and can supply over 35 amps of continuous
current. Refer to figure 21 (golf ball is for size compar-
sion). It is enclosed in the legendary McIntosh Potted
Enclosures and weighs over 12.06kg. The super size main
filter capacitors can store over 600 Joules of energy for the
five amplifier channels, necessary for the wide dynamic
range that “Digital Audio” demands. The power amplifier
draws high current from the AC power line. Therefore, it is
important that they plug directly into the wall outlet.
Also, most owners desire one power switch for the whole
audio system. The MC1.2KW is equipped with a circuit
that provides remote Power Control from a McIntosh
A/V Control Center. When the A/V Control Center is
switched On, a (+5V) signal operates the power relay in
the MC1.2KW. The MC1.2KW also has a remote Power
Control Out Jack. The Power Control signal from this jack
is delayed by a fraction of a second so that the turn on
power surge of the next power amplifier occurs at a later
time. This helps prevent power circuit overload that could
trip circuit breakers or blow fuses, a very important feature
in a high power Home Theater System employing three or
more MC1.2KW Power Amplifiers.
Figure 21
Figure 18
Without Power Guard
Figure 19
With Power Guard
Figure 20
CIRCUIT
BREAKER
Block Diagram
of the
Power Supply