I am also very interested in this, i use C64G with 1541 Ultimate II+ and want to play C64 lead solos (Cynthcart) on my MIDI masterkeyboard, but situation is more complicated that it seems, because although i have Cynthcart cartridge, but older version 1.2 ordered from AtariAge (btw is no longer for sale on that site) and i don't want newer cartridge because software can be downloaded from author's site so there is no need to exchange cartridge which i always hated.

http://sharewareplus.blogspot.sk/2016/0 … lable.html

Here is Datel MIDI interface which works with Mini Xpander+, cartridge bridge which is tested for example with Cynthcart, so you can have plugged two cartridges to C64, but it is NOT compatible with 1541 Ultimate II+.

Aside of this, 1541 Ultimate II+ features some USB slots (i use one of them for 16GB usb stick), i asked creator of this magic device if one of ports can be used for USB-MIDI connection, but up to now i got no reply so probably it is not possible, so i now have no solution, i nevermind

Thanks, I'll keep the HerMIDI one in mind too.

These interfaces are exactly the ones emulated in the kerberos interface (http://www.frank-buss.de/kerberos/users-guide.pdf), so yeas they appear to be amongst the most popular.
Station64 (http://djindikator.net/c64/v24/sta64.txt) emulates them too, in addition to HerMIDI.

Just out of interest, which of the midi interfaces/protocols are people using on the c64?   Looking at the specs they all have a similar setup though the addresses spaces change a bit.   There appear to be 4 I've found info on:

Sequential Circuits
Passport
Datel
Namesoft