Headphone Class A Amplifier


t is a very useful thing , to have a small headphone amplifier , capable of driving a couple of pairs phones. Fortunately, the headphone amp has a much easier job to do, in that neither the output power requirements nor the load characteristics are so severe, since headphones typically have a load, impedance , higher of 50 ohm, (typical 600 ohm), and only require 1-2V RMS. max, for normal output. Since only a low power output is required, a Class A stage, is perfectly feasible. For adequate Class A operation the output transistors Q5-6, should pass say 100mA each. With ±15V supply this would mean 1.5Watts dissipation, so a smallish Heatsink, will be needed for each. With RV1 adjust input audio signal and Tr1 adjust the output DC Offset voltage for 0V (±30mV). For stereo application , you need two unit, of this amp.

Circuit diagram

Circuit diagram

Part List

  • R1-4= 1.2Kohm
  • R2-3= 3.9Kohm
  • R5=100Kohm
  • R6-10= 10Kohm
  • R7-9= 2.2Kohm
  • R8= 150 ohm
  • R11-13= 6R8 ohm
  • R12= 4.7 ohm
  • R14=68Kohm
  • RV1= 10Kohm Log. pot.
  • TR1= 10Kohm Trimmer
  • C1= 4.7uF 63V MKT
  • C2-7= 100uF 25V
  • C3-5= 100nF 100V MKT
  • C4-6= 100uF 16V
  • C8-10= 470uF 25V
  • C9-11= 100nF 100V ceramic
  • Q1-3= BC184
  • Q2-4= BC214
  • Q5= BD136 or BD538
  • Q6= BD135 or BD537
author: L. Hood
circuit from http://users.otenet.gr/~athsam/headphone_2.htm