balanced circuitry. The resulting double balanced configu- ration cancels even order distortion. Refer to figure 12 on page 13.
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.
The output signals of the two balanced circuits are coupled together in the unique McIntosh MC602 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 MC602 con- tributes to low operating temperatures. More than 290 square inches of heat sink area keep the MC602 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.
The Autoformer creates an ideal match between the power amplifier output stage and the loudspeaker. A McIn- tosh amplifier with an Autoformer can be used to safely drive multiple speakers without reducing the life expect- ancy of the
power ampli- fier. Refer to figure 13.
There is ab- solutely no per- formance limi- tation with an Autoformer. Its frequency re-
Figure 13
sponse exceeds that of the output circuit itself, and extends well beyond the audible range. Its distortion level is so low it is virtually impossible to measure.
In the rare event of a power amplifier output circuit fail- ure, the McIntosh Autoformer provides absolute protection from possible damage to your valuable loudspeakers. The unequaled expertise of McIntosh in the design and manu- facturing of Autoformers is legendary in the high fidelity industry. McIntosh engineers know how to do it right.
Protection Circuits
The MC602 incorporates it’s version of the McIntosh Sen- try Monitor output transistor protection circuit. Refer to Figure 14. There is absolutely no compromise in sonic per- formance with this circuit, and it ensures safe operation of the amplifier under even the most extreme operating condi-
Figure 14
tions. The different types of protection circuits incorpo- rated in the MC602 insure a long and safe operating life. This is just one of the many characteristics of McIntosh Power Amplifiers that make them world famous.
The MC602 also includes the unique patented McIntosh Power Guard circuit.
Power Guard eliminates the possibility of ever overdriving the amplifier into clipping. Refer to figures 15, 16 and 17. An overdriven amplifier can produce both audible and inaudible distortion levels exceeding 40%. The au- dible distortion is un- pleasant to hear, but the inaudible ultrasonic dis- tortion is also undesir-
14