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Sunday, August 12, 2007

Headphone Amplifier

Headphone Amplifier

Circuit diagram:

Amplifier parts:
P1_____________22K   Log.Potentiometer (Dual-gang for stereo)
R1____________560R 1/4W Resistor
R2,R3__________10K 1/4W Resistors
R4_____________12K 1/4W Resistor
R5,R6___________2R2 1/4W Resistor
R7_____________22R 1/2W Resistor
C1______________1µF   63V Polyester Capacitor
C2,C3,C4______100µF 25V Electrolytic Capacitors
C5_____________22pF 63V Polystyrene or Ceramic Capacitor
C6_____________22µF 25V Electrolytic Capacitor
IC1___________LM833 or NE5532 Low noise Dual Op-amp
Q1,Q3_________BC337 45V 800mA NPN Transistors
Q2,Q4_________BC327 45V 800mA PNP Transistors
J1______________RCA  audio input socket

Power supply parts:

R8______________2K2  1/4W Resistor
C7,C8________2200µF 25V Electrolytic Capacitors
D1____________100V 1A Diode bridge
D2____________5mm. or 3mm. Red LED
IC2___________7815  15V 1A Positive voltage regulator IC
IC3___________7915 15V 1A Negative voltage regulator IC
T1____________220V Primary, 15 + 15V Secondary 5VA Mains transformer
PL1___________Male Mains plug
SW1___________SPST Mains switch


  • 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 Ohm.
  • Old 8 Ohm impedance headphones can be also driven, but these obsolete devices are not recommended.
  • Schematic shows left channel and power supply (common to both channels).
  • Numbers in parentheses show IC1 right channel pin connections.
  • A correct grounding is very important to eliminate hum and ground loops. Connect to the same point the ground sides of J1, P1, C2, C3 & C4. Then connect separately the input and output grounds to the power supply ground.

Technical data:

Output voltage: Well above 5V RMS into all loads

Sensitivity: 250mV input for 5V RMS output

Frequency response: Flat from 30Hz to 20KHz

Total harmonic distortion @ 1KHz & 10KHz:
Below 0.005% into 32 Ohm loads and up to 4V RMS output (typical 0.003%)

Total harmonic distortion @ 1KHz & 10KHz:
Below 0.005% into 100 to 2000 Ohm loads and up to 5V RMS output (typical 0.003%)

Unconditionally stable on capacitive loads

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