Revised the place of the power amplifier board.

Powered up the USB Hub and the tablet from "non-native" sources.
Unfortunately, I can allocate one day a week for these classes, the process is slow...
In addition, I tested the sound subsystem - speakers and D-class amplifier. Everything works, but the feeling of the predominance of medium and high frequencies.
In addition, the 13cm speakers are possibly redundant.
This is a consequence of the lack of a clear understanding of what the unit is made for - quiet home music making or playing at a noisy party)))