This is a nice amplifier and very easy to make it. Its an 20W Audio Amplifier based on LM1875 IC.
Power supply - 48 VDC
Output - 20 W, 4 ?
Very low distortion (THD - 0.015%), good channel separation and ripple rejection
IC built-in thermal, short circuit protections
Internal output protection diodes
Terminal pins for connecting input
Power Battery Terminal (PBT) for easy power supply and speaker connection
Power-On LED indicator
Heatsink for IC
Four mounting holes of 3.2 mm each with nut and stud
PCB dimensions 48 mm x 60 mm