Audio Engineering

314 Chapter 10

predecessors. At about the same time, DC-coupled amplifi ers began to take over from
capacitor-coupled designs, as the transistor differential pair became a more familiar
circuit element.

A much fuller and generally excellent history of power amplifi er technology is given in
Sweeney and Mantz.^2

10.2 Amplifi er Architectures.........................................................................................

This grandiose title simply refers to the large-scale structure of the amplifi er, that is, the
block diagram of the circuit one level below that representing it as a single white block-
labeledpower amplifi er. Almost all solid-state amplifi ers have a three-stage architecture
as described here, although they vary in the detail of each stage.

10.3 The Three-Stage Architecture ...............................................................................

The vast majority of audio amplifi ers use the conventional architecture, shown in
Figure 10.1. There are three stages, the fi rst being a transconductance stage (differential

First stage,

input

subtractor and

gain

Second

stage,

voltage

amplifier

Third stage,

output

 

Figure 10.1 : The three-stage amplifi er structure. There is a transconductance stage, a

transadmittance stage (the VAS), and a unity-gain buffer output stage.