This headphones amplifier circuit can deliver up to 1W on a 8Ω headsets. A stereo headset is connected, in generally, to an amplifier output through a voltage divider. This simple solving solution has 2 disavantages: the sound intesity cannot be adjusted independently from the speakers and the voltage divider lowers the attenuation factor for the headset which translates in bass altering.


This problem can be solved with a final stage amplifier similar to this, equiped with 2 power transistors, BD139 and BD140.


Headsets amplifier circuit diagram

headphones amplifier
So, this headphones amplifier can output a total power of 1 Watt, so the power supply must be designed for 300mA. The amplification factor depends on R4 and R5, its value is approximately equal to 11. With P2 we adjust the voltage in R12/R14 common point at half of the power supply. In idle mode the current through final transistors is 50 to 100 mA. Other rest currents can be attained by modifying the R8