Technical Description - McIntosh MC7106 Owner's Manual

DESIGN PHILOSOPHY
The MC7106 Six Channel power amplifier is designed to operate loudspeakers with a
nominal impedance of 4 to 8 ohms. It features a new circuit design that keeps distortion levels
so low it takes special test gear for accurate measurements.
The design philosophy incorporated in this outstanding amplifier involved many different
techniques, all based on sound scientific logic. Every stage of voltage or current amplifica-
tion was designed to be as linear as possible. Negative feedback is then utilized to enhance
the performance. Mclntosh engineers know how to properly design negative feedback circuits
so they contribute to the extremely low distortion performance expected from a Mclntosh
amplifier. All transistors are selected to have nearly constant current gain (Beta) over the en-
tire current range they must cover. Output transistors in particular, have matched uniform
current gain, high current-bandwidth product and large active region safe operating area.
Resistors and capacitors in the signal path are carefully selected to have exceedingly low
voltage coefficients, (change of resistance or reactance with applied voltage). Precision metal
film resistors, low dielectric absorption film capacitors and premium audio grade electrolytics
are used in all critical circuit locations.
PROTECTION CIRCUITS
Some manufacturers claim that their products do not need or use protection circuits and
that such circuits compromise performance. Mclntosh feels that protection circuits are
desirable and necessary to prevent amplifier or loudspeaker damage due to abnormal cir-
cumstances. The genius of Mclntosh engineering has resulted in protection circuits which
have no effect or compromise on the normal performance of a power amplifier. The SENTRY
MONITOR circuit is a good example. The MC7106 incorporates six specific protection cir-
cuits to enhance its performance, increase its reliability and protect loudspeakers.
SENTRY MONITOR CIRCUIT
All power transistors have limits for the maximum amount of power they can handle. The
MC7106 output transistors and power supply have been designed to allow very high current
flow into properly matched load impedances. However, if a short circuit or very low load im-
pedance is connected to any of the MC7106 outputs, destructive current levels could be reach-
ed if it was not controlled by the SENTRY MONITOR circuit- This circuit senses the dynamic
operating time, voltage and current of the output stage, and controls it to safe operating limits.
There is absolutely no compromise in sonic performance and it ensures safe operation
of the amplifier under even the most extreme operating conditions.
THERMAL CONTROL
All power transistors have limits for the maximum amount of heat they can safely tolerate.
The MC7106 uses highly efficient amplifying circuits which produce relatively little heat for
the output power produced. The amplifier uses large area heat sinks to efficiently dissipate
what heat it does generate. Natural convection air flow is sufficient for safe cool operation.
If the cooling air is blocked, or the amplifier operating temperature is forced too high, ther-
mal cutout switches will turn off the speakers on one or more pairs of channels. Both POWER
GUARD indicators will light continuously for the channels that are affected to show that ther-
mal protection is operating. When the problem is corrected and the amplifier cools down to
its normal operating temperature, the speakers will be turned back on.
TECHNICAL
DESCRIPTION
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