Review on DAMGOO Bluetooth 50W+50W Stereo Audio Amplifier Board: Wireless DIY Speakers with Treble and Bass Control, BT 5.0, AUX Inputs - Easy Installation, Password Free by Nicolai Goler

I ran this from a 19V 5A power supply and connected it to a pair of good quality bookshelf speakers. I can't turn the volume up past 1/4 without getting a lot of distortion. As a test, I hooked up my cheap 1990's boombox to the same speakers and it put out about the same amount of pure power before going into the distortion range. The Boombox is rated at 8 watts/channel at 8 ohms. According to the specifications of this amp, it should deliver 20 watts into 8 ohms at 19 volts applied, which almost certainly isn't the case.