Chapter 18. Audio

18.0 Introduction

Audio electronics is all about generating signals and amplifying them enough to power a loudspeaker so that you can hear them.

This chapter contains a number of amplification and signal-generation recipes. Any resource that deals with audio-power amplifier design will explain the different classes of amplifiers, which are designated by A, B, AB, and D, and some other more exotic designs. For the most part, these letters designate how the amplifier is constructed from bipolar junction transistors and how they are biased. Since these days there is no real cost or even quality advantage (apart from the most demanding audiophile) to building an amplifier from separate transistors rather than just using an IC, I feel it is only necessary here to highlight the most common designs along with their main characteristics:

Class A
Low distortion but very inefficient, produces a lot of heat.
Class B and AB
A push-pull design. More distortion than A but much more efficient. AB is the same as B but with compensation to reduce the distortion when the amplifier switches over from pushing the loudspeaker to pulling it (see Recipe 18.4)
Class D
Digital amplifier. Higher distortion than A or B but very energy efficient (see Recipe 18.5)

Before launching into the construction of your own amplifier designs, think about whether you need to build the amplifier from scratch. For most one-off projects, it is easier and cheaper to use ready-made modules or even USB-powered ...

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