36
is so low it is virtually impossible to measure. In the
rare event of a power amplifier output circuit failure,
the McIntosh Autoformer provides absolute protection
from possible damage to your valuable loudspeakers.
Power Output Meter
The McIntosh MA8000 has large Output Watt Meters
that respond 95% full scale to a single cycle tone burst
at 2kHz. Refer to figure 88. The Voltage Output is
electronically measured and fed to a special circuit
that accelerates the pointer movement in the upward
direction. 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.
Protection Circuits
The MA8000 incorporates its version of the McIntosh
Sentry Monitor output transistor protection circuit.
Refer to figure 89. There is absolutely no compromise
in sonic performance with this circuit, and it ensures
safe operation of
the amplifier un-
der even the most
extreme operating
conditions. The
different types of
protection circuits
incorporated
in the MA8000
insure a long and
safe operating life.
The MA8000
also includes the unique patented McIntosh Power
Guard circuit. Power Guard eliminates the possibility
of ever overdriving the amplifier into clipping. Refer
to figures 90, 91 and 92.
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 unde-
sirable, since it can dam-
age 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 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 ampli-
fier 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 absolutely no au-
dible side effects and the
sonic purity of the music
reproduction is perfectly
preserved. The MA8000
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.
Figure 91
Without Power Guard
Figure 90
Input Test Signal
(14kHz & 15kHz)
Figure 89
Normal Operating Area
Sentry Monitor
Safety Area
Output
Transistor
Failure
Figure 92
With Power Guard
Figure 88
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