Specifications

deliver large quantities of power when they are clipping
but they have more than 40% harmonic distortion. In
this mode, the sound is grossly distorted and the extra
energy content of the clipped signal will damage most
loudspeakers. The Mclntosh Power Guard circuit
protects your ears and your speakers from this kind of
damage.
The Power Guard circuit consists of a waveform
comparator which monitors the wave shape of the
amplifier input and output signals. Normally there is no
disparity between these signals and the comparator
produces no output. When the amplifier is driven
beyond its maximum power capacity a difference will
develop. If the disparity exceeds 0.3% (equivalent to
0.3% total harmonic distortion) the comparator output
causes the amber POWER GUARD indicator to light.
If there is a further increase in the disparity the
comparator output controls an electronic attenuator at
the amplifier input to reduce the amplifier gain, thus
holding the amplifier output to a low distortion value.
Overdrive by 14dB is possible before the output
distortion exceeds 2%.
SENTRY MONITOR
All power transistors have limits for the maximum
amount of power they can handle. The MC7100 output
transistors and power supply have been designed to
allow very high current flow into properly matched load
impedances. If, however, a short circuit or very low
value of load impedance is applied to the output of the
MC7100, destructive current levels could be reached
if it was not controlled by the Sentry Monitor circuit.
This circuit senses the dynamic operating time, voltage,
and current of the amplifier output stage and controls
the current flow confining it to nondestructive limits.
Sentry Monitor does not limit the power output available
from the amplifier.
THERMAL CONTROL
All power transistors have limits for the maximum
amount of heat they can tolerate. The MC7100 uses
a highly efficient amplifying circuit which produces
relatively little heat for the output power produced. The
amplifier has oversized heatsinks to dissipate transistor
generated heat. Natural convection airflow is sufficient
for cool operation. Should the cooling air be blocked
or should the amplifier operating temperature become
too high, thermal cutouts within the amplifier will turn
off the speakers. Both POWER GUARD indicators
will light continously to show thermal protection is
operating. When the amplifier has cooled, it will
automatically turn on again.
TURN-ON DELAY
The MC7100 has a turn-on delay circuit that
delays amplifier operation for about 2 seconds after
power turn on. This prevents pops or thumps generated
in other equipment from causing annoying noises or
damaging your loudspeakers.
DIRECT CURRENT FAILURE PROTECTION
A circuit is provided that turns off the speakers
if for any reason a DC voltage appears at the speaker
terminals. This prevents speaker damage.
POWER LINE INRUSH PROTECTION
Turn on inrush current is cushioned by a
thermistor in the power transformer primary circuit. A
soft start is achieved that eliminates component stress
during turn-on.
CIRCUIT OPERATION
The audio input passes through the gain control
to the power guard attenuator. The output amplifier
follows the attenuator.
The power output amplifier uses two stages of
voltage amplification followed by three stages of current
amplification. All stages are complimentary balanced.
Even number harmonics are canceled by the balanced
circuits. This means that the amplifying stages have
less total harmonic distortion and less negative feedback
is required to achieve ultra low distortion.
The signal is fed to one input of the balanced
differential stage. Feedback from the amplifier output
is applied to the other input. The differential amplifiers
drive a balanced cascode connected voltage amplifier
stage. Current mirrors are also used to improve
bandwidth and linearity.
The cascode voltage amplifier output feeds
complementary Darlington connected driver transistors.
These supply the signal to 4 complementary connected
output transistors per channel. Ancillary components
for Power Guard, Sentry Monitor and other protection
circuits interconnect with the amplifier circuits. The
power supply uses a massive power transformer, full
wave bridge rectifiers and large filter capacitors having
50 joules of energy storage. Large heatsinks provide
cooling for the 8 output power transistors.
The mechanical and electrical design of the
MC7100 is the result of the many years of engineering
and manufacturing experience held by the staff at
Mclntosh. This "know how", the meticulous attention
to design and production details, makes the MC7100
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903
MC7100 Product Preview/Page 5