The MonkMakes Powered Speaker is an easy to use amplified speaker on a PCB.
The board needs a 5V power supply that can be provided by a Raspberry Pi or Arduino. Audio input will normally be to the 3.5mm stereo audio jack socket, which is mixed to a mono signal as there is just a single speaker on the board.
A direct audio connection (AC coupled) is also provided by the pin labeled AUDIO next to the power pins.
Please note that the AUDIO pin is not suitable for direct connection to unfiltered logic-level PCM that you might produce from a Raspberry Pi. It is however just fine for something like the audio output of a FM receiver or MP3 player module.
Here’s the schematic, so that if you are interested, you can see exactly what’s going on.
This board is also sold as part of a kit intended for use with a Raspberry Pi.