userfriendly wrote:Btw, am I right in assuming that the circuit of this input extension would get its current from the external connector to the MegaDrum?
Yes, on the EXT connector pin 1 is VCC, pin 2 is ground. Here's Synthex mainboard scheme: http://www.megadrum.info/forums/viewtopic.php?f=3&t=456 EXT is in the upper part of the middle.