www.megadrum.info

When I finish the configuration I'll close the megadrum borad inside a drum, so I'll see the configuration only by a computer if will be neccesary ... so it's better to supply the board with the MIDI 5Volt or with a external power supply connect to the USB port?

I'm not sure I understand the question correctly but yes, you can power MegaDrum over USB using any regulated 5V 500mA power supply.