Figure 5-21. Ideal Frequency-response Curve for an Audio Amplifier
5-81. Figure 5-22 shows the first single-stage audio amplifier. This circuit is a class A,
CE, RC-coupled, transistor, audio amplifier. C1 is a coupling capacitor that couples the
input signal to the base of Q1. R1 is used to develop the input signal and provide bias for
the base of Q1. R2 is used to bias the emitter and provide temperature stability for Q1. C2
is used to provide decoupling (positive feedback) of the signal that would be developed by
R2. R3 is the collector load for Q1 and develops the output signal. C3 is a coupling
capacitor that couples the output signal to the next stage. VCC represents the collector-
supply voltage. Since the transistor is a CE configuration, it provides voltage amplification.
The input and output signals are 180 out of phase. The input and output impedance are
both medium. 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 chapter.
Figure 5-22. Class A, CE, RC-coupled, Transistor, Audio Amplifier
23 June 2005