McIntosh MC1201 User Manual

Page 13

Technical Description

Design Philosophy

The design philosophy incorporated in the MC1201 in-

volved several different techniques, all based on sound sci-

entific logic. Every stage of voltage or current amplifica-

tion must be as linear as possible prior to the use of nega-

tive feedback. McIntosh engineers know how to properly

design negative feedback circuits 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.

Double Balanced Push-Pull design is used from input to

output. Each half of the amplifier contains complimentary

balanced circuitry. The resulting double balanced configu-

ration cancels even order distortion. Refer to figure 12.

All transistors are selected to have nearly constant cur-

rent gain over the entire current range they must cover.

Output transistors in particular, have matched uniform cur-

rent gain, high current bandwidth product and large active

region safe operating area. An automatic tracking bias sys-

tem completely eliminates any trace of crossover distor-

tion. Precision metal film resistors and low dielectric ab-

sorption film capacitors are used in all critical circuit loca-

tions.

Figure 12

The output signals of the two balanced circuits are

coupled together in the unique McIntosh MC1201 Output

Autoformer. It provides low distortion power transfer at

frequencies 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 MC1201 con-

tributes to low operating temperatures. More than 290

square inches of heat sink area keep the MC1201 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 optimum load

may vary considerably from what a loudspeaker requires.

In the case of more than one loudspeaker connected in par-

allel, 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

output stage. This increase in temperature will result in a

reduced life expectancy for the amplifier.

Block Diagram

of the

Amplifier and Meter Circuitry