Class A Headphone Amplifier 12V 5V

The circuit is a two-stage amplifier with the output transistor operating in linear A mode with a quiescent current of approximately 180 mA. The entire amplifier consists of OOS circuit (elements C5, R5, R6). The resistances of resistors R5 and R6 determine the gain of the node. The output transistor must be mounted on a small heatsink.
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To obtain high-quality sound, capacitor C2 must be film, and capacitors C6, C7 must have low ESR. For best results, it can be achieved by connecting several capacitors in parallel.

Class A Headphone Amplifier specifications

Rated supply voltage 12V
Rated output power (RLOAD = 32R) 0.25W
Harmonic distortion (F = 1 kHz) 0.01%
Rated frequency range 20 – 20,000 Hz
Current consumption of one channel 180 mA

Current consumption depends on resistor R7. The higher the quiescent current, the better the sound at the amplifier output. A 33 Ohm resistor with a 12V supply will give a current of approximately 180 mA. This value is absolutely sufficient to achieve excellent load damping.

The printed circuit board is made directly for the stereo version. Isolating resistor R8 – consists of two 0.25 watt 10 ohm resistors. Each channel has its own decoupling circuit, providing slightly improved stereo separation (similar to the dual mono principle).

The output transistors are mounted on a common aluminum plate with a thickness of 1.5 – 2.0 mm through insulation spacers. Headphone jack ST-215N. Trimmer resistor R1 type 3396W, terminal blocks type DG127, DG128 or XY304. PCB prepared with P-CAD 2006.

There is a 5V powered version of the Class A Headphone Amplifier circuit as an alternative to the 12V version (no PCB drawing)

Source: mariolla.com/index.php/amplifier/10-mrl-1308.html