Lossless audio 4-to-1 switcher (no common ground)

B station video: https://www.bilibili.com/video/BV1Ft4y177BH/
1. Introduction
Using 74HC139 as a logic controller and signal relay as an audio switcher for switching, physical switching, nearly lossless,
suitable for only one speaker device, multiple speakers Input device switching scenario, with key switch, power off and mute, volume adjustment,
 
I have done a switching using CD4052 before, but 4052 has a big problem, that is, there will be crosstalk when the input is greater than 1V.
For example, if the CH0 input is greater than 1V and the channel is switched to CH1, you will hear the sound of CH0 crosstalking to CH1. This is a chip problem, and CD4052 can only pass AC signals, so it cannot be processed separately, so the simplest and violent method is Use signal relay to switch, physical switching to avoid interference
2. The block diagram
is relatively simple, mainly the logic control device 74HC139
3.
Since LAYOUT transmits audio analog signals, pay special attention to interference during wiring
4. Shell