Design and production of class AB headphone amplifier

The low-distortion headphone amplifier introduced in this article is an improved version of the commonly used op+ current expansion.

The signal is low-pass filtered by R1,2/C1 and then sent to the op amp. The right channel output consists of IC and transistors Q1,2,3,4. The quiescent current of the amplifier is determined by Q1,4/R9,10. The output stage is a complementary push-pull amplifier with a static current of 8ma, and negative feedback is obtained through R3,4, R5,6.

The sine wave undistorted output test is as follows:

Pure resistance load output voltage output power RMS
32ou5.5v 950mw
150ou8.8v520mw
330ou9.8v 300mw
680ou 10v150mw

The power supply adopts positive and negative dual power supply, the circuit is shown in the figure:

A simple three-terminal voltage regulator is connected in parallel to output, and LM431 is used to raise the fixed voltage of Yuan7815.

Due to the use of OCL structure amplification, in order to protect the safety of the headphones, a power-on delay and a zero-point voltage offset protection circuit are designed, as shown in the figure:

Using the high on-voltage characteristics of the field effect tube, it is easy to design the RC delay circuit, and the actual delay time is 1S.

The actual test is also satisfactory: