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hifi headphone amplifier circuit schematic

HiFi Headphone Amplifier Circuit

heaphone amplifier replacementsThis HiFi headphone amplifier circuit design is normally used to drive a headphone with a relative low impedance. It provides one watt power output and it can also be applied as an output stage for preamplifiers in conjuction with active loudspeakers boxes. The headphone amp is composed of an OP-AMP and an additional transistor amplifier. Input signals pass through a low pass filter composed of R1-C2. Its applification together with a relatively “fast” OPAMP provides a low distortion factor.

The standby current is preset by diodes D1…D4 and R7-R8. The feedback resistors R3 and R4 set the amplification factor at about 15 dB. The distorsion factor is aound 0.1 % with a bandwidth of 10 Hz to 30 kHz.

headphone amp transistors

The headphone amplifier provides a maximum output of 1 watt to an 8 ohm load by an input level of 500 mV. High impedance headphones can be connected. The circuit can also drive a 4 ohm speaker.

Headphone amp circuit diagram

hifi headphone amplifier circuit schematic

In order to prevent the output transistors from being destroyed in case of an output short circuit, they must be heatsinked. The transistors must also be electrically isolated from heatsink. Supply voltage can be provided by an adaptor with 6-8 volts DC output.

Headphones amplifier PCB layout

headphones amp pcb

5 Comments

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  • anatoly

    and also if opamp and out transistors are in “a”class mode this circuite will be about 0,1 – 0,15 distortion under 30-50 mW (on 25 oms like denon headphones)and freaquences over 2kHz. its possible to reduse amount gain to 2, but transcient responce will bad and need rebalance output dc level.
    talking about denons, output resistance is due to be less 2 ohm for sharp bass

  • anatoly

    sorry,,,,
    1.output resistance over 10 ohm
    2.r5,r8,c4 – phase and frequency unlinear correction
    3.D1-D4 – add noise and harmonic distortion
    4. input resistance should be 10-22koms to avoid cable influence and lose impulse transcient responce
    try max9718/lm 4871 – not “a” class define sound in headphones, wich has own 0,2 – 0,5% distortion

  • tito

    hello iwant to construct this circuit can u give more details about it and give me all components that need it to make it

  • rafal

    well it has to be powered from symetric power supply i mean +/- and ground, so for ex. 2 ff 9v batteries. 2 years later hovewer eager to help 😉

  • AcroMan

    i’ve contructed this circuit but it doesint work for me :/ then i connect ir to the 9V battery and play music..i hear lot of noise and quite music…does some one know ?

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