Noise and Grounding
Douglas Self13.1 Audio Amplifi er Printed Circuit Board Design ....................................................
This section addresses the special printed circuit board (PCB) design problems presented
by power amplifi ers, particularly those operating in Class-B. All power amplifi er systems
contain the power-amp stages themselves, and usually associated control and protection
circuitry; most also contain small-signal audio sections such as balanced input amplifi ers,
subsonic fi lters, output meters, and so on.
Other topics related to PCB design, such as grounding, safety, and reliability, are also
dealt with.
The performance of an audio power amplifi er depends on many factors, but in all cases
the detailed design of the PCB is critical because of the risk of inductive distortion due
to cross talk between the supply rails and the signal circuitry; this can very easily be the
ultimate limitation on amplifi er linearity, and it is hard to overemphasize its importance.
The PCB design will, to a great extent, defi ne both the distortion and the cross talk
performance of the amplifi er.
Apart from these performance considerations, the PCB design can have considerable
infl uence on ease of manufacture, ease of testing and repair, and reliability. All of these
issues are addressed here.
Successful audio PCB layout requires enough electronic knowledge to fully appreciate
the points set out here so that layout can proceed smoothly and effectively. It is common
in many electronic fi elds for PCB design to be handed over to draftspersons, who, while
very skilled in the use of CAD, have little or no understanding of the details of circuit
operation. In some fi elds this works fi ne; in power amplifi er design it will not because
CHAPTER 13