Began making a "bluetooth speaker". Using a BT receiver I found that comes with left & right RCA outputs and an 1/8 inch jack, too; USB-micro and USB A jacks, too. It worked well with the Grunding.
Removed the BT pairing (red) and status (blue) LEDs as well as the main pushbutton, which serves as power and as a means of initializing pairing and re-establishing a BT connection, for relocation on the speaker's front panel.
I'm going to build an amplifier for it using the LM4871 (*2) which is designed for 5V. Not certain whether I'll have a panel-mounted pot because I won't know how much actual gain it has, how much control I'll need, till I build it. I am satisfied that the concept is sound, based on my test using my Archer amplifier.
Built up one experimental channel of the LM4871 amp on the old breadboard.
Decent volume with 20kΩ R_fdbk, but better with 33kΩ. No "0.39µF" for that input cap, but there's a range given for that (0µ1 to 0µ47) - so I used two 0µ1 in parallel [0µ2].
I didn't bother with the 'Shutdown' pull up, just tying pin 1 to GND.