When designing such an instrument, you do lots of tests, and finally you end up using only one half of the components you bought. Here is a small list of 9 components I finally won't use:

1. I won't try to hack an existing USB cable again:

   

   I'm probably not so good at stripping cables, but wires in USB cables are so thin that even if you manage to strip them, at the end, you'll have wires that are so thin that they would break easily. I lost some time trying to do it, it was such a mess! Let's use a 1€ USB PCB connector + Dupont cables. 10 times better and more robust.

2. A panel-mount USB socket (~ 10€):

   

   As I'm using a PCB for I/O board, this part won't be needed anymore. Having to screw such a socket to the enclosure is finally probably a bad idea. A PCB-mounted 1€-USB-socket is finally better.

3. A plain 7-segment display without micro-controller:

   

   They are cheap (1 or 2€ on ebay) but they would require to be connected to the Pi with 12 pins, and would require a constant running task to update (maybe 60 times per second!) the display. Some people tried (I don't find the link anymore) and it used at least 10% of the Raspberry Pi's CPU. Bad idea. It's better to use this 7-segment PCB. A little bit more expensive, but it's easier to use it.

4. This jack-power plug won't be needed:

   

   Powering the SamplerBox is now done with a classical 5V phone charger with micro USB.

5. A hacked MIDI/USB interface:

   

   Not needed anymore because we can connect directly the MIDI input to the Raspberry Pi's serial port (UART RX pin), with a little bit of work (configuring the data baud rate, etc.).

6. 4 AA batteries holder:

   

   This might be too big to fit in the enclosure. Currently looking for a smaller and/or better solution.

7. Several enclosures:

   

   Using these enclosures would have been cool, but we would have needed to laser-cut the holes anyway. So if laser-cutting is needed anyway, why not using directly custom made enclosures? One less thing to buy: enclosure.

8. This DAC is really excellent (wonderful sound quality and cheap ~10€) but it won't be needed...

   

   ... simply because I have found this DAC which is a) based on the same PCM2704 chip (so same sound quality), b) cheaper (6€), c) smaller!

9. I know it'll sound weird but it was quite hard to find very short USB cable:

   

   Not needed since I have now built shorter cables myself.