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
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 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
