The second prototype boards came today and they're almost ideal.

As I mentioned in the last log, I do think I'll back down from a buck converter to an LDO to make the 3.3v power for the controller and GPS, but the addition of the preamp improved the range of output loudnesses available - making more of the range of the adjustment pots usable.

I am going to change a pair of component values, however. The preamp only needs to have 5x gain instead of 10, so that means dropping the feedback resistor from 200kΩ to 100kΩ. The audio (to my ears anyway) sounds a bit less tinny changing the LPF feedback cap on the final amp from 2200pF to 0.01µF.

But that's about it. With the larger speaker, I wouldn't call the volume "room filling" in the same sense as a stereo, but it's certainly loud enough to serve the purpose. If I did a better job recording the audio samples, that would probably help quite a bit too.