USB sound card + Bluetooth 5.0 module (the actual product has been made and the function has been verified)

Use pcm2706 for USB to IIS, pcm1794a for DAC: and then use BTM308 Bluetooth module for Bluetooth function design of a hifi sound card. The power supply was originally dual power supply. I thought dual power supply was troublesome, so I added a reverse boost to the PCB to generate negative voltage. The 12v power supply circuit makes a single power input a convenient power supply choice. Bluetooth uses the qcc3008 chip to support lossless coding and decoding technology, and the wireless sound quality is guaranteed. The wireless connection enable pin of the chip makes a Bluetooth connection and automatically disconnects the wired and non-device connection. automatically switches to wired

Note: The schematic diagram has been adjusted according to the actual circuit and the PCB has been completely updated

1. Pitfalls encountered when making physical objects

1. Power supply part

The pitfalls encountered were mainly due to errors in the selection of D2 and D1 diodes. The original selection of FR107G fast recovery diodes directly resulted in low voltage and severe jitter problems. Finally, D2 and D1 were replaced with SS34 Schottky type diodes before the voltage returned to normal. : It is also possible to use other Schottky diodes with the same parameters.

2..Bluetooth

The main problem I encountered in the wireless aspect was that the Bluetooth module did not support push-button startup, and I only designed the push-button startup and not the automatic startup after power-on, which caused the Bluetooth to fail to turn on. I only found out this cruel fact after asking the Bluetooth module seller. Finally, I added the automatic startup circuit. It's normal now: Now on the schematic diagram, the button to start the computer has been removed and it has been replaced by automatic power-on.

2. Feeling of use

1. Noise floor

Thanks to the excellent power supply design, this sound card has no audible noise from headphones or speakers when only connected to the power supply (switching power supply) and audio output without a USB cable. There is no audible noise when the USB cable is connected to the computer to play music. I can hear the background noise, but there is still audible background noise for a few seconds when the music is about to end. When the USB cable is connected to the mobile phone through the OTG adapter to play music, this phenomenon needs to be improved a lot. The noise floor of Bluetooth is smaller than that of wired to the point where it is hard to hear. level reached

2. Sound quality

There is actually not much difference between USB wired sound and Bluetooth wireless sound. Although the noise floor of USB wired is louder than Bluetooth, the sound of USB is more beautiful and the dynamic range is larger. Compared with the onboard sound card, the improvement is quite obvious.

bilibili platform demonstration video

Baidu Netdisk platform demonstration video