Audio Engineering

Preamplifi ers and Input Signals 191

This implies that a “ push–pull ” arrangement, such as the so-called “ long-tailed pair ”
circuit shown in Figure 7.22 , which tends to cancel second harmonic distortion
components, will greatly improve the distortion characteristics of such a stage.

Also, because the output voltage swing for a given input signal (the stage gain) will
increase as the collector load ( R 2 in Figure 7.22 ) increases, the higher the effective

Vb 0 .7V

l(mA)c Vb^0

.65 V

Vb 0 .6V

Vb 0 .55 V

Vb 0 .5V

Collector voltage (Vc)

Figure 7.21 : Output current/voltage characteristics of a typical silicon bipolar transistor.

V

V

R 2

R 1

R 3

R 4 (R 1 )

0V 0V

Eout

Q 1 Q 2

Ein

Figure 7.22 : Transistor voltage amplifi er using a long-tailed pair circuit layout.