Owner`s manual

35
conditions with the benefits of lower distortion and
cooler operation. Precision metal film resistors and
low dielectric absorption film capacitors are used in
all critical circuit locations. Refer to figure 86
The output signal of the circuit is coupled together
in the unique McIntosh MA8000 Output Autoformer.
It provides low distortion power transfer at frequen-
cies from below 20Hz to well beyond 20,000Hz with
optimum impedance points of two ohms, four ohms
and eight ohms. The unequaled expertise of McIntosh
in the design and manufacturing of autoformers is
legendary in the high fidelity industry.
The high efficiency circuit design of the MA8000
contributes to low operating temperatures. More
than 1,000 square inches of heat sink area keep the
MA8000 operating safely with convection cooling. No
fans are needed.
Autoformers
All solid state power amplifier output circuits work
best into what is called an optimum load. This op-
timum load may vary considerably from what a
loudspeaker requires. In the case of more than one
loudspeaker connected in parallel, the load to the
power amplifier may drop to two ohms or even less. A
power amplifier connected to a load that is lower than
optimum, causes more output current to flow, which
results in extra heat being generated in the power out-
put stage. This increase in temperature will result in a
reduced life expectancy for the amplifier.
The Autoformer creates an ideal match between
the power
amplifier output
stage and the
loudspeaker.
Refer to figure
87. There is
absolutely no
performance
limitation with
an Autoformer.
Its frequency
response ex-
ceeds that of
the output cir-
cuit itself, and
extends well
beyond the au-
dible range. Its
distortion level
circuit into either the feedback or input section of the
equalizer amplifier. This provides a 12dB boost or cut
at the frequency of the tuned circuit. The overall gain
of the stage is 0dB when the potentiometer is at its
center detent position. In this position the tone control
elements are completely removed from the signal path.
Power Amplifier Design Philosophy
The design philosophy incorporated in the MA8000
involved several different techniques, all based on
sound scientific logic. Every stage of voltage or cur-
rent amplification must be as linear as possible prior
to the use of negative feedback. McIntosh engineers
know how to properly design negative feedback cir-
cuits so they contribute to the extremely low distortion
performance expected from a McIntosh Amplifier.
The typical McIntosh owner would never accept the
approximately 100 times higher distortion of many
non-feedback designs. Refer to figure 84.
All transistors are selected to have nearly constant
current gain over the entire current range they must
cover. The 12 Power Transistors used in each channel
of the MA8000 Power Output Circuitry, have matched
uniform current gain, high current bandwidth product
and a large active region safe operating area. These
Power Transistors are the very latest in semiconductor
technology and incorporate a new design
known as ThermalTrak™. Refer to figure
85. This allows for the instantaneous and
accurate monitoring of the Power Tran-
sistor Temperature. The MA8000 Power
Output Circuitry has a specially designed
bias circuit to take full advantage of the
ThermalTrak™ Power Transistors and
thus precisely controls the power ampli-
fier operation over a wide range of music
Technical Description, con’t
Figure 86
Figure 87
Figure 85