I have recently develop this PCB it is used to make unbalanced audio signal in to balanced, this allows
to use amplifiers in bridge output configuration "mono".I have here this module mostly for the PA150
amplifier boards "LM3886" but it can be used for other audio amp modules, it is operated with +15 and-15
Volts.Pictures with assembled parts as an example.
If you enjoy this kind of stuff you could check here:
https://www.ebay.de/usr/dialedinmusic?_trksid=p4429486.m3561.l2559