# Sixth Lichuang Electric Competition# Mini single power supply analog small power amplifier

 1. Introduction to project functions

It uses a low-power analog power amplifier composed of a triode and an operational amplifier, which sounds good.
Generally used for listening to music in a quiet indoor environment, the effect is very good.

A power-on delay circuit is added to disconnect the relay when the power is turned off to reduce the popping sound.

The PCB design is drawn using the single-point grounding method commonly used in power amplifiers.

2. Project attributes

It was released for the first time. It was partly based on the SOLO headphone amp circulating on the Internet and modified to increase the power. Improved power on and off without POP sound.

3. Open source agreement

GPL3.0

4. Hardware part

1) The power supply part of the op amp adopts a capacitance multiplication circuit, which has small ripple and provides stable and clean power supply to the op amp.

2) The power supply part adopts DC5.5 power socket (12-24V power supply). Use PMOS as a soft switch to reduce power-on shock. Extend the life of the toggle switch (SW1).

Multiple electrolytic capacitors are connected in parallel to reduce capacitance ESR and provide stable and abundant power supply.

3) The speaker output circuit uses a double-pole double-position relay. After turning on the power switch (SW1), the capacitor CP8 is charged through R57 and D5. The relay closes after about 2 seconds to achieve power-on delayed output.

Prevented the POP sound when powering on. When shutting down, it discharges quickly through R58 and quickly disconnects the relay. Realize shutdown to prevent POP sound.

4) Power amplifier circuit, resistors R4, R25, and R7 provide a bias of VCC/2 to the operational amplifier. Adjust potentiometer R25 so that the voltage at the output terminal of the potentiometer is (VCC/2).

The op amp uses AC feedback and has an amplification factor of 3.55 times. Transistors Q1 and Q2 push-pull output, D1 and D4 prevent crossover distortion.

Input capacitor (C8 or C18, choose one), output capacitor (C23 in parallel with CP9) and feedback capacitor (CP11 in parallel with C12) affect the sound quality, so use better quality capacitors.

5. Software part

6. BOM list

7. Contest LOGO verification

 8. Demonstrate your project and record it as a video for uploading

The power tube and aluminum casing use thermal pads to conduct heat.

The casing uses an aluminum profile casing, and the front and rear panels are PCB panels. It uses the same shell as the two previous open source amplifiers.

https://www.bilibili.com/video/BV1rg411L7uk/