McIntosh MC300 Owner's Manual

POWER GUARD
Power Guard, a unique feature of Mclntosh amplifiers, assures that each channel of the
MC300 will deliver full power free of clipping distortion. Clipping is caused when an amplifier
is asked to produce more power output than its design is capable of delivering with low distor-
tion. Amplifiers that are overdriven may deliver large quantities of power when they are clip-
ping, but they may 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 elec-
tronic 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
MC300 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 MC 300, 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
MC300 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 cool-
ing 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 MC300 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 caus-
ing 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
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TECHNICAL
DESCRIPTION

McIntosh MC300 Specifications

General

Brand	McIntosh
Model	MC300
Category	Amplifier
Language	English