■ FIGURE 2. This heatsink is adequate.
ground (0.1 µF ceramic). The ground for these should be run
separately back to that quality ground point, as well.
My perf board assembly has an added RCA jack and
potentiometer stuck on the corner for testing (Figure 4). The 0.22
ohm resistors are in one package with leads running out both
ends for convenience in measuring the voltages. Standard single
wire wound resistors may be used as well, of course. Mouser has
five watt units for 44 cents each.
I placed parts roughly as they appear on the schematic.
This makes circuit tracing much easier. The top of the board in
Figure 6 corresponds to the top of the schematic. You will want a
power switch and fuse on the primary side of the power
transformer; 3,300 µF capacitors are adequate for both versions
of the amplifier. By using the larger ones, you will get a watt or
two more out of the amplifier before clipping. You will need to
use a slow blow fuse because at turn-on, the filter capacitors
essentially look like a shortcircuit as they charge. I suggest two
amps. A fuse will not protect the output transistors against an
output shortcircuit, but will blow if the power supply is shorted.
This power amplifier is Class B. Class B amplifiers introduce
what is called crossover distortion. When the output signal is
negative, the PNP output device conducts. When it is positive,
the NPN conducts. Crossover distortion is generated at the point
where the conduction crosses over from one output transistor to
■ FIGURE 3.