13 - Unchained Melody — Amplifiers

Abstract

This chapter provides an introduction to amplifier designs. The perfect audio amplifier should possess a very high input impedance so as to avoid the loading upstream equipment, and a very low output impedance so as to damp the loudspeaker oscillations. Moreover it should possess a power output suitable for reproducing a realistic dynamic range, at least equivalent to that possessed by a 16-bit digital audio. The power amplifier transforms the electrical signals at an operating level of a few volts pk-pk across 600 Ω to a signal of perhaps a few hundred volts pk-pk across as small an impedance as possible, which is typical of the signal required to drive a moving coil loudspeaker. Power amplifiers may be divided into two main classes—Class A and Class B—and a third type of power amplifier is known as a current dumping amplifier. A Class-A amplifier has a single circuit devoted to producing both the positive half and the negative half of the musical sounds, and a Class-B amplifier has two circuits, one devoted to handling the positive going halves of each cycle, the other devoted to handling the negative portions of the signal.