After a few months on this project, a lot of feedback (thanks everyone!) and some long holidays in Italia with both sun and rain (yes this is our tent but surprisingly all was fine 2 hours later!),

it's now time to think about the big picture of the project (by the way, bigpictu.re is another project of mine: if you like mind maps, or an infinite panning and zooming whiteboard, you're gonna like it!).

What was the initial goal of SamplerBox?

1. to be able to jam anywhere with a portable instrument,
2. for hours,
3. without having to connect many cables and many other stuff, i.e. the goal was all-in-oneness,
4. to have great sound quality, low latency, high polyphony,
5. to be able to load 500MB+ piano sample sets,
6. to have fast boot like on every normal synthesizer.
    

What is currently achived? What is not?

I think #4 and #5 are done, thanks to the RaspberryPi, a good cheap USB DAC, and my not-too-bad code (I spent some time on code optimization to allow high polyphony). After some work, #6 is now ok as well.

About #3, my dream would be to be able to build an all-in-one keyboard + SamplerBox unit, like this (or maybe 3 octaves instead?):

Let's call it SamplerBox Keyboard. I'd like to have your feedback about this! What do you think? Would you like such a unit?
Anyway, this is probably for later.

Now the main problem for me is #2 : if we want many hours of battery life, we need expensive and/or big size batteries. I don't like this idea. Maybe we need to change the whole board: RaspberryPi is cool but not for having the device run for 10+ hours with a 5.5cm x 4cm x 0.5cm battery (the size of my phone's battery):

So right now my main question is: is there a board that is able to run Linux, is small-sized, has some good CPU, and can run 10+ hours on battery? Yes smartphones are like this! Does this exist in the form of a board (in the fashion of Arduino, RaspberryPi, Teensy, etc.)? I need your help about this!

About #1, I'd need to experiment more with small-sized loudspeakers.