McIntosh MC1201 - Manual (Page 15)

15
Technical Description, con’t
Figure 18
With Power Guard
Figure 17
Without Power Guard able, since it can damage
valuable loudspeaker sys-
tem tweeters. You will
never experience the
harsh and damaging dis-
tortion due to clipping.
The Power Guard cir-
cuit is a waveform com-
parator, monitoring both
the input and output
waveforms. Under nor-
mal 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 wave-
forms. When the difference exceeds 0.3% (equivalent to
0.3% harmonic distor-
tion), the Power Guard
activates the PG light and
a dynamic electronic at-
tenuator at the amplifier
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 pu-
rity of the music repro-
duction is perfectly pre-
served. The MC1201 Power Amplifier with Power Guard
is not limited to just the rated power output, but will actu-
ally produce distortion free output well above its rated
power due to the McIntosh philosophy of conservative de-
sign.
Power Supply Circuits
To compliment the fully balanced design of the MC1201
there are two high voltage power supplies; one for each of
the two amplifier circuits, allowing each amplifier circuit
to be optimized using its own power supply. Refer to figure
19. High power amplifiers draw high current from the AC
power line. Therefore, it is important that they plug directly
into the wall outlet.
Also, most owners desire that there be one power
switch for the whole audio system. The MC1201 is
equipped with a circuit that provides remote Power Control
from your McIntosh Preamplifier or Control Center. When
you turn on your preamplifier a digital “1” (+5V) signal
operates the power relay in the MC1201. The MC1201 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 Sys-
tem employing three MC1201 Power Amplifiers.
The MC1201 can provide greater than 200 amperes
peak output current to drive uneven speaker loads. Some
poor speaker designs have input impedance that dip to 1 or
2 ohms at various frequencies and the MC1201 has the out-
put current reserve to drive them. It can deliver over 1,000
Watts Output on tone bursts. The MC1201 has huge main
filter capacitors that guarantee an excellent signal to noise
ratio and the energy storage necessary for the wide dy-
namic range that “Digital Audio” demands.
Figure 19
Block Diagram
of the
Power Supply