This simple headphone amplifier circuit can be directly connected to other compact devices such as CD player, Walkman, Tuners and tape recorder. In theory, the series of headphones amplifier circuit is able to work well on different impedances. The impedance is 32 ohm, 100, 300, 600, and 2000 ohm. The shown circuit scheme is for one channel (mono). If the stereo will be built live two series.
As shown in the figure, components B1, SW1, J1 and C3 are for both channels if stereo is to be made. The resistor value R3 has been calculated for 300 ohm impedance. If it will be used for 600 ohm impedance or higher, change the resistor value R3 to 100K. Actually Battery B1 can be replaced with power supply if possible, provided it is well regulated.
If the battery is still in use, the battery type can be replaced with rechargeble. The listed R3 values for 300 ohm and 600 ohm impedances are for 3.7 Volts. When used with batteries in a stereo system, the battery will usually drain within 20 hours.
Portable headphone amplifier based 3 transistors parts list:
- R1 = 10K
- R2 = 100K
- R3 = 68K
- R4 = 1.5K
- R5 = 3.3K
- R6 = 330R
- R7 = 4K7
- R8 = 2.2R
- C1 = 1µF-63V
- C2 = 100µF-25V
- C3 = 470µF-25V
- Q1 = BC239C
- Q2 = BC337
- Q3 = BC327
- J1,2 = Stereo 3mm. Jack socket
- SW1 = SPST Switch
- B1 = 3V Battery (two 1.5V AA or C cells in series, but see Notes)
