Radio Headphone Amplifier

Providing a high input impedance, reasonable gain and volume limiting this radio headphone amplifier is a good choice for homebrew radio circuits.

Resistor R2 pulls up the voltage at the base of Q1 to the supply rail voltage however that only pulls up the voltage at the emitter of Q2 to the supply rail voltage minus about 1.4 V (2 base emitter junction voltage drops), An input signal higher than the positive supply rail in to the base of the Darlington pair (Q1, Q2) can increase the emitter voltage beyond that. 

The output voltage swing (after start up) is then limited to 1.4 volts minus the saturation voltage of Q2, about 0.2 volts.

The voltage swing limit then across the headphones is about 1.2 volts, if that is still too much you can add an additional resistance in series with headphones to protect your ears from impulse noise etc. from homebrew radio circuits.

Unfortunately there is a loud  start up pulse through the headphones.  You should connect the headphones and start the circuit before listening.  A possible partial solution might be 2 diodes in series between the positive supply rail and C3 charging it rapidly to 1.4 volts to below the supply rail at start up, diverting most of the charging current away from the headphones.