Love what you're doing here!
The input jack has three tabs for two wires. One tab is the tip, does it matter which of the other tabs is selected?
What about adding a similar output jack for an external speaker cabinet?
Is there a way to set it up where the output would go directly to self-contained speaker, unless the jack was in use, in which case output would go through the jack? Should this be hard to do? Any thoughts on how?
Similarly, on the power supply, is there a way to put in automatic switching between a wall wart and the AA battery box?
Let me know what you think.