The balance control, Fig. 18.2 makes it possible in streophonic systems to vary the voltage gain in both channels by 6 dB in opposite directions. The controlling variable resistor is inserted in the feedback circuit. The average gain is 23.4 dB. The differences in the total distortion for minimum and maximum gain are slight because of the large amount of feedback applied. The frequency response (–3 dB points) is from <20 Hz to >20 kHz, while the input and output impedances are 140 kΩ and 85 Ω respectively.
Fig. 18.2 Stereo balance control circuit (only one channel shown)