Power amplifier and headphone amplifier mini 2-in-1 V2.0

1) Use PD or DC port to power 12V-24V.
2) Integrated Class D power amplifier and headphone amplifier, digital volume.
3) Two-way audio input selection, headphone output, and power amplifier output selection.

Using 4-layer boards, board layout is convenient and the performance is better. (Thanks to Jialichuang and its friends for the free PCB)

The I2C interface is introduced, which can be connected to an external OLED (SSD1306) that is easy to purchase.

The source program is completely open source.

-------------------------------Happy Singles' Day in advance----------------- -------------

After 5 months of cooing, the second version was finally updated. Mainly improves the sound quality. Like the previous version, HK32F030M is used as the main control.

1) Removed the PT7313 of the previous version (which somewhat affects the sound quality, especially when using headphones). Using SGM3157 analog switch and CAT5171 digital potentiometer to select the input channel and volume control, the left and right channels can be controlled independently.

2) Use LTC722 operational amplifier for single-ended to differential amplification, and use TPA3116 to improve the noise floor.

3) The mute control of TPA6138 has been changed to PNP logic, which has eliminated the POP sound of the headphones that occasionally occurred when turning on and off the previous version.

4) The 3.3V LDO is modified to a better MIC5205.

Hardware BUG:

The TPA6138 headphone amplifier has missing coupling capacitors. When welding, put a 2.2uF capacitor in series before R56 and R61. Pull down the 51K resistor after the capacitor to AGND (2021.10.26). Fortunately, no flying wires are needed.

Software: (source program)AMP-2.0-2021.10.23

2021.10.23 The hardware verification was completed, and all functions are only displayed on the home page. Basically available.

Volume and balance control logic needs to be updated.

The OLED display adds a reverse display function and a progress bar display.

Overvoltage, undervoltage, and overtemperature protection have been added.

The program needs to be updated and improved.

----------------------------------The above edited on 2021.10.23---------- -----------------------

Updated program: (source program)AMP-2.0-2021.10.25

In the main interface, you can directly press the left and right keys to set the volume.
Completed the logic of volume balance setting.                
The left and right volumes can be set independently and take effect immediately after setting.
When the overall volume or balance changes, the left and right volumes are calculated and not set individually.

Added software shutdown reset.

The program is basically usable. The program is written relatively amateurishly. . . . . . for reference only.

Please post pictures of how to fix hardware bugs. . . . . . . . .

The same shell and front and rear panels as the old version.

Add another waveform of the differential output of the op amp.

Listen to the video

https://www.bilibili.com/video/BV1CT4y1R7bg

----------------------------------The above edited on 2021.10.26---------- -----------------------