Figure 1-23.Transistor audio amplifier.
There is nothing new presented in this circuit. You should understand all of the functions of the
components in this circuit. If you do not, look back at the various sections presented earlier in this
The second single-stage audio amplifier is shown in figure 1-24. This circuit is a class A,
common-source, RC-coupled, FET, audio amplifier. C1 is a coupling capacitor which couples the input
signal to the gate of Q1. R1 is used to develop the input signal for the gate of Q1. R2 is used to bias the
source of Q1. C2 is used to decouple the signal developed by R2 (and keep it from affecting the source of
Q1). R3 is the drain load for Q1 and develops the output signal. C3 couples the output signal to the next
stage. VDD is the supply voltage for the drain of Q1. Since this is a common-source configuration, the
input and output signals are 180º out of phase.
Figure 1-24.FET audio amplifier.