Here’s a very cheap audio amplifier, from the usual suspects in Shenzhen. This is a Herdio AMP-BTX01 Bluetooth Audio Amplifier. This is a stereo unit, but the quality is going to be piss poor!
Cracking the casing, which is just clipped together reveals the sparsely populated PCB. There’s a 12v power input on the right, along with a line-level input. The speaker outputs are on the left. Between the two are only a few components to do the audio signal processing.
There’s just the Bluetooth radio IC, an AC21BP0A931. Not much is available on this IC, I certainly can’t find a datasheet, but it has all the low-level audio stuff, a microcontroller & a 2.4GHz Bluetooth radio integrated into a single IC. There’s a 5v linear regulator hiding behind the electrolytic caps to provide a power rail for this. The only other components here are a ruck of SMD ceramic coupling capacitors in the audio lines to the amplifier ICs.
The final components are these Chinese FET audio amplifier ICs, rated at 15W per channel, and driving a speak each in Bridge mode – these are stereo amps.