This is a schematic for a MIDI Adapter designed to work with the Sound Blaster joystick (ie, game) port. It should also work with any card having a compatible joystick port.

Parts

4 resistors. 3 will have values of 220 ohms, and 1 with a value of 2200 ohms
1 Diode (1N4148)
1 74LS00 IC (ie, contains 4 NAND gates)
1 OptoIsolator (CNY17, or a 6N138 or Sharp PC900 may be substituted with
    changes as noted)
2 female DIN jacks (or you can use male DIN plugs if you wish to connect
    directly to the MIDI device without extra MIDI cables)
1 male 15 pin MINI DB connector (to plug into the sound card's gameport)

Schematic

Copyright notice

This circuit has been placed into the public domain. You may freely distribute it, and use it in any product you create.

Disclaimer

This circuit is provided "as is" without warranty of any kind either expressed or implied or tatooed in a place that only a few people have ever seen, including but not limited to the implied warranties of merchantability, fitness for a particular purpose, and the dubious assumption that the circuit has been created by a sane individual who would never do anything that may hurt you. The entire risk as to the results and performance of the circuit is assumed by you or someone who looks exactly like you. Jeff Glatt does not guarantee that the operation of this circuit will meet your requirements, especially if your requirements involve lots of latex and some docile, domesticated animal. Nor does Jeff Glatt warranty the circuit to be uninterruptable or error-free, although mercifully free of "Pompous Ass Copyright Holder" hassles. If you use said circuit, you can not say anything nasty about the author nor Jeff Glatt, even if the circuit inadvertently causes the erasure of your collection of X-rated GIFs of a conservative, overweight and overrated TV "personality" plooking himself vigorously with his royalty checks from some rancid paperback. Jeff Glatt is not responsible for any damages as a result of anything that he has done, or hasn't done, or was supposed to do but never got around to it, and furthermore, he doesn't even care so leave him alone, sewer mold. You may have more or less protections in certain states of the union, depending upon how far your local politician is willing to bend over for some bribe from a business lobbyist. Just remember that Jeff Glatt has no money, so don't bother suing him as a result of any damages caused by this circuit. Tell your greasy lawyer to go after Creative Labs, and make sure that you pick 12 really stupid pinheads for the jury. If swallowed, induce vomiting immediately by contemplating the performance of Sound Blaster MIDI.

Sound Blaster is a trademark of Creative Labs. They can have it.