McIntosh MC402 - Manual (Page 17)

17
Technical Description
tion. Refer to Figure 22.
The MC402 also includes the unique patented McIntosh
Power Guard circuit. Power Guard eliminates the possibil-
ity of ever overdriving the amplifier into clipping. Figures
23, 24 and 25 are actual Spectrum Analyzer measurements
of a McIntosh Power Amplifier,
with a test signal consisting of
14kHz and 15kHz sine waves. An
overdriven amplifier can produce
both 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, monitoring
both the input and output wave-
forms. Under normal operating
conditions, there are no differ-
ences between the shape of these
waveforms. If an amplifier chan-
nel is overdriven, there will be a
difference between the two signal
waveforms. When the difference
exceeds 0.3% (equivalent to 0.3%
harmonic distortion), the Power
Guard activates the PG light and a
dynamic electronic attenuator at
the amplifier input reduces the in-
put volume just enough to prevent
any further increase in distortion.
The Power Guard circuit acts so fast that there are abso-
lutely no audible side effects and the sonic purity of the
music reproduction is perfectly preserved. The MC402
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 MC402,
there are huge main filter capacitors that guarantee an ex-
cellent signal to noise ratio and the energy storage neces-
sary for the wide dynamic range that “Digital Audio” de-
mands.
Figure 23
Input Test Signal
Figure 24
Without Power Guard
Figure 25
With Power Guard
tributes to low operating temperatures. More than 2,000
square inches of heat sink area keep the MC402 operating
safely with convection cooling. No fans are needed.
Autoformers
All solid state power amplifier output circuits work best
into an optimum load. This optimum load may vary consid-
erably from what a Loudspeaker requires. In the case of
more than one Loudspeaker connected in parallel, the load
to the power amplifier may drop to two ohms or even less.
A power amplifier connected to a load that is lower than
optimum, causes more output current to flow, which results
in extra heat being generated in the power output stage.
This increase in temperature will result in a reduced life
expectancy for the amplifier.
The Autoformer creates an ideal match between the
power amplifier output stage and the Loudspeaker. A
McIntosh amplifier with an Autoformer can be used to
safely drive multiple speakers
without reducing the life ex-
pectancy of the power ampli-
fier. Refer to Figure 21.
There is absolutely no per-
formance limitation with an
Autoformer. Its frequency re-
sponse exceeds that of the out-
put circuit itself, and extends
well beyond the audible range.
Its distortion level is so low it
is virtually impossible to mea-
sure.
In the rare event of a power amplifier output circuit fail-
ure, the McIntosh Autoformer provides absolute protection
from possible damage to your valuable Loudspeakers. The
unequaled expertise of McIntosh in the design and manu-
facturing of Autoformers is legendary in the high fidelity
industry. McIntosh engineers know how to do it right.
Protection Circuits
The different types of protection circuits incorporated in
the MC402 insure a long and safe operating life. This is
just one of the many character-
istics of McIntosh Power Am-
plifiers that make them world
famous. The MC402 incorpo-
rates the McIntosh Sentry
Monitor Output Transistor Pro-
tection Circuit, which protects
the amplifier in the event of a
shorted Loudspeaker Connec-
Figure 21
Figure 22