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Both = halves=20 of the circuit are identical. Both inputs have a dc path to ground via = the input=20 47k control which should be a dual log type potentiometer. The balance = control=20 is a single 47k linear potentiometer, which at center adjustment = prevents even=20 attenuation to both left and right input signals.
If the balance = control=20 is moved towards the left side, the left input track has less resistance = than=20 the right track and the left channel is reduced more than the right side = and=20 vice versa. The preceding 10k resitors ensure that neither input can be=20 "shorted" to earth.
Amplification of the audio signal is = provided by a=20 single stage common emitter amplifier and then via a direct coupled = emitter=20 follower. Overall gain is less than 10 but the final emitter follower = stage will=20 directly drive 8 ohm headphones. Higher impedance headphones will work = equally=20 well.
Note the final 2k2 resistor at each output. This removes = the dc=20 potential from the 2200u coupling capacitors and prevents any "thump" = being=20 heard when headphones are plugged in. The circuit is self biasing and = designed=20 to work with any power supply from 6 to 20 Volts DC.