TABLE OF CONTENTS Testing power amplifiers for correct operation is relatively easy; faultfinding them when something is wrong is not. I have been professionally engaged with power amplifiers for a long time, and I must admit I still sometimes find it to be a difficult and frustrating business.
There are several reasons for this. First, almost all small-signal audio stages are IC-based, so the only part of the circuit likely to fail can be swiftly replaced, so long as the IC is socketed. A power amplifier is the only place where you are likely to encounter a large number of components all in one big negative feedback loop. The failure of any components may (if you are lucky) simply jam the amplifier output hard against one of the rails, or (if you are not) cause simultaneous failure of all the output devices, possibly with a domino-theory trail of destruction winding through the small-signal section. A certain make of high-power amplifier in the mid-70s was a notorious example of the domino-effect, and when it failed (which was often) the standard procedure was to replace all of the semiconductors, back to and including the bridge rectifier.
Component numbers here refer to Figure 6.13.
By far the most important step to successful operation is a careful visual inspection before switch-on. As in all power amplifier designs, a wrongly installed component may easily cause the immediate failure of several others, making fault-finding difficult, and the whole experience generally less than satisfactory. It is...
