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How to build A Hiqh Quality Headphone Amplifier Schematic

2015-01-04 17:22  
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Some lovers of High Fidelity headphone listening prefer the use of battery powered headphone amplifiers, not only for portable units but also for home "table" applications. This design is intended to fulfill their needs. An improved output driving capability is gained by making this a push-pull Class-B arrangement. Output power can reach 100mW RMS into a 16 Ohm load at 6V supply with low standing and mean current consumption, allowing long battery duration.

Circuit diagram:

Circuit diagram


P1 = 22K PotentiometerR1 = 15K ResistorR2 = 100K ResistorR3 = 100K ResistorR4 = 47K ResistorR5 = 470R ResistorR6 = 500R ResistorR7 = 1K ResistorR8 = 18K ResistorR9 = 18K ResistorR10 = 2.2R ResistorR11 = 2.2R ResistorR12 = 33R ResistorR13 = 4.7K ResistorC1 = 10uF-25V CapacitorsC2 = 10uF-25V CapacitorsC3 = 100nF-63V (PF)C4 = 220uF-25V CapacitorsC5 = 100nF-63V (PF)C6 = 220uF-25V CapacitorsQ1 = BC560C PNP TransistorQ2 = BC560C PNP TransistorQ3 = BC550C NPN TransistorQ4 = BC550C NPN TransistorQ5 = BC560C PNP TransistorQ6 = BC327 PNP TransistorQ7 = BC337 NPN TransistorJ1 = RCA Audio Input SocketJ2 = 3mm Stereo Jack SocketB1 = 6V Battery RechargeableSW1=SPST Slide or Toggle Switch


For a Stereo version of this circuit, all parts must be doubled except P1, SW1, J2 and B1.Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to maximum resistance and Trimmer R3 to about the middle of its travel.Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.Switch on the supply and measure the battery voltage with a Multimeter set to about 10Vdc fsd.Connect the Multimeter across the positive end of C4 and the negative ground.Rotate R3 in order to read on the Multimeter display exactly half of the battery voltage previously measured.Switch off the supply, disconnect the Multimeter and reconnect it, set to measure about 10mA fsd, in series to the positive supply of the amplifier.Switch on the supply and rotate R6 slowly until a reading of about 3mA is displayed.Check again the voltage at the positive end of C4 and readjust R3 if necessary.Wait about 15 minutes, watch if the current is varying and readjust if necessary.Those lucky enough to reach an oscilloscope and a 1 KHz sine wave generator can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed.

Technical data:

Output power (1 KHz sine wave):16 Ohm: 100mW RMS32 Ohm: 60mW RMS64 Ohm: 35mW RMS100 Ohm: 22.5mW RMS300 Ohm: 8.5mW RMS


160mV input for 1V RMS output into 32 Ohm load (31mW)200mV input for 1.27V RMS output into 32 Ohm load (50mW)

Frequency response @ 1V RMS:

Flat from 45Hz to 20 KHz, -1dB @ 35Hz, -2dB @ 24Hz

Total harmonic distortion into 16 Ohm load @ 1 KHz:

1V RMS (62mW) 0.015% 1.27V RMS (onset of clipping, 100mW) 0.04%

Total harmonic distortion into 16 Ohm load @ 10 KHz:

1V RMS (62mW) 0.05% 1.27V RMS (onset of clipping, 100mW) 0.1%Unconditionally stable on capacitive loads

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