Portable Headphone Amplifier
3V Battery powered
High Performance unit
Circuit diagram:
Parts:
R1_____________10K 1/4W Resistor
R2____________100K 1/4W Resistor
R3_____________68K 1/4W Resistor (see notes)
R4______________1K5 1/4W Resistor
R5______________3K3 1/4W Resistor
R6____________330R 1/4W Resistor
R7______________4K7 1/4W Resistor
R8______________2R2 1/4W Resistor
C1______________1µF 63V Polyester Capacitor
C2____________100µF 25V Electrolytic Capacitor
C3____________470µF 25V Electrolytic Capacitor
Q1____________BC239C 25V 100mA NPN High-gain Low-noise Transistor
Q2____________BC337 45V 800mA NPN Transistor
Q3____________BC327 45V 800mA PNP Transistor
J1____________Stereo 3mm. Jack socket
SW1___________SPST Switch
B1____________3V Battery (two 1.5V AA or C cells in series)
Notes:
- Can be directly connected to CD players, tuners and tape recorders.
- Tested with several headphone models of different impedance: 32, 100, 245, 300, 600 & 2000 Ohms.
- Schematic shows left channel only.
- B1, SW1, J1 & C3 are common to both channels.
- R3 value was calculated for headphone impedance up to 300 Ohms. Using 600 Ohms loads or higher, change R3 value to 100K.
Technical data:
Current drain: 35mA per channel with 32 Ohms impedance headphones. Much less with higher impedance loads
Output voltage: Above 2V peak-to-peak on all loads
Sensitivity: 90mV RMS input for 2V peak-to-peak output
Frequency response: Flat from 30Hz to 20KHz
Total harmonic distortion @ 1KHz & 10KHz: Below 0.05% on 32 to 600 Ohms load and up to 1.5V peak-to-peak output. Below 0.1% at maximum output
Unconditionally stable on capacitive loads
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