The Maplin Electronic Circuits Handbook, 2nd Edition

96 AMPLIFIERS

diodes, D

:

and D

2

. TR

3

thus acts as a constant current source to the

emitters of TRj and TR

2

. This ensures symmetry since the total collector

current of TR

X

and TR

2

remains constant, i.e. if the collector current of

TR

{

increases by a certain amount (due to an increase in signal current)

the collector current of TR

2

must fall by the same amount.

RV

X

sets the emitter current of TR

X

and TR

2

and, since TRj is d.c.

coupled to the base of TR

4

, it can be used to adjust the symmetry of the

output stage in the same manner as that provided by RV

{

in the circuit

of Figure 4.37.

Bootstrapped feedback is applied via C

5

while C

4

provides negativ ...