Technical Description - McIntosh MA6400 Owner's Manual

DESIGN PHILOSOPHY
The design philosophy incorporated in the MA6400 involved many different techniques, all
based on sound scientific logic. Every stage of voltage or current amplification is 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. The typical
Mclntosh owner would never accept the approximately 100 times higher distortion of many so
called non- feedback designs.
All transistors are selected to have nearly constant current gain (Beta) over the entire current
range they must cover. Output transistors in particular, must 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 power amplifier manufacturers claim that their products do not need or do not 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 circumstances. The genius of Mclntosh engineering has resulted in protection
circuits which do not effect or compromise the normal performance of a power amplifier.
Five different types of protection circuits are incorporated in the MA6400 to insure it a long,
safe and trouble free operating life. This is just one of the characteristics of Mclntosh power
amplifiers that have made them world famous. The SENTRY MONITOR circuit is a good example.
SENTRY MONITOR CIRCUIT
All power transistors have limits for the maximum amount of power they can handle. The
MA6400 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 impedance
were connected to the MA6400 outputs, destructive current levels could be reached if it was not
controlled by the Mclntosh SENTRY MONITOR circuit. This circuit senses the dynamic operating
time, voltage and current of the output stage, and controls it to safe operating limits. The
SENTRY MONITOR circuit does not limit the power output available from the amplifier.
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 to the maximum amount of heat they can safely tolerate. The
MA6400 uses highly efficient amplifying circuits which produces relatively little heat from the
TECHNICAL
DESCRIPTION
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