Specifications

from the amplifier
THERMAL CONTROL
All power transistors have limits for the
maximum amount of heat they can tolerate The
MC7300 uses a highly efficient amplifying circuit
which produces relatively little heat for the output
power produced The amplifier has 4 oversized
heatsinks to dissipate transistor generated heat
Natural convection air flow 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 power to the amplifier When the amplifier
has cooled, it will automatically turn on again
TURN-ON DELAY
The MC7300 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
The autotransformer protects speakers from
damage in the event of amplifier failure. Should a
direct current component appear in the output it is
shunted by the autotransformer and DC cannot reach
the speaker
POWER LINE INRUSH PROTECTION
Turn on inrush current is cushioned by
thermistors 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 a preamplifier. The output amplifier is driven by
the preamplifier
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 cancelled 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 10 com-
plementary connected output transistors per channel
Ancillary components for Power Guard, Sentry
Monitor, Power Output Meters and other protection
circuits interconnect with the amplifier circuits. The
power supply uses a massive power transformer, full
wave bridge rectifiers Large filter capacitors having
227 joules of energy storage Four large heatsinks
provide cooling for the 20 output power transistors.
The mechanical and electrical design of the
MC7300 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
MC7300 one of the finest amplifiers ever produced
by Mclntosh Laboratory
Issued by Engineering Department
May 1991
MC7300 Product Preview/Page 7
MclNTOSH LABORATORY INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903