Headphone Amplifier Class A: 1.5V Output, 0.5% Distortion

Regardless of the circuit's simplicity, all conditions concerning distortion and frequency response are thoroughly evaluated. The input resistance measures 250K ohms, while the driving load ranges from 100 ohms to 2K ohms. The circuit employs negative coupling. The output operates in Class A, utilizing the BC308 integrated circuit as its active element alongside a 39R resistor. A current bias of approximately 14mA to 15mA is implemented. The circuit provides a gain of 25. The power supply voltage can be adjusted from 6V to 24V DC. The frequency response with a 200R load exhibits a range of 37Hz to 470kHz (-1dB), generating an output voltage of 1.5V (11mW) and exhibiting a distortion of 0.5%.

Integrated Circuit Description

The BC308 is a general-purpose NPN bipolar junction transistor widely used in audio amplifiers and other low-power circuits. It's a three-terminal device consisting of a base, a collector, and an emitter. This transistor acts as the active element within the circuit, amplifying the signal and providing the desired gain. Its characteristics include a moderate gain, making it suitable for a variety of amplifier applications. The BC308 is known for its reliability and relatively low cost, contributing to its widespread use.

Circuit diagram