I see no reason it shouldn't work.

only midi input needs an opto isolator so if your just doing output, should be ok. I dont know if soundcard gameports had opto isolators or not.

Isolator is only necessary if you want to avoid ground loop stuff, but for gameport to gameport you simply connect TTL signals to one-another. Isolator etc. is supposed to be in the cable, and not on the sound card.

Thank you! Will report here the success (or lack of it), but might be a few weeks before I can delve into the matter.

When I saw this post, I made a DB15 crossover cable as you mentioned to test it.

I used it with my 486 PC with SB16 connected to the gameport of a Vibra128 on an Athlon XP 2200+ and it worked with both MidiPlayer5 and Munt.
In Munt I had problems with the music with some instruments missing, but it was fixed by loading the file "MT32_GM_Mode.syx"

It was only necessary to weld the Rx, Tx and GND.

rflego wrote on 2020-08-19, 02:27:

When I saw this post, I made a DB15 crossover cable as you mentioned to test it. […]
Show full quote

When I saw this post, I made a DB15 crossover cable as you mentioned to test it.

I used it with my 486 PC with SB16 connected to the gameport of a Vibra128 on an Athlon XP 2200+ and it worked with both MidiPlayer5 and Munt.
In Munt I had problems with the music with some instruments missing, but it was fixed by loading the file "MT32_GM_Mode.syx"

It was only necessary to weld the Rx, Tx and GND.

That is great, but I would still be worried that without some sort of isolation, a delta between ground levels might result in a ground loop sufficient to damage something . That said, I am far from an expert in these matters .

darry wrote on 2020-08-19, 04:32:

rflego wrote on 2020-08-19, 02:27:

When I saw this post, I made a DB15 crossover cable as you mentioned to test it. […]
Show full quote

When I saw this post, I made a DB15 crossover cable as you mentioned to test it.

I used it with my 486 PC with SB16 connected to the gameport of a Vibra128 on an Athlon XP 2200+ and it worked with both MidiPlayer5 and Munt.
In Munt I had problems with the music with some instruments missing, but it was fixed by loading the file "MT32_GM_Mode.syx"

It was only necessary to weld the Rx, Tx and GND.

That is great, but I would still be worried that without some sort of isolation, a delta between ground levels might result in a ground loop sufficient to damage something . That said, I am far from an expert in these matters .

On desktop PCs, ground is connected to protective earth, so the differences between ground in different PCs is a couple of 100millivolts at max. This is enough to ruin your day if you have an line-level analog audio connection, but is unproblematic if you just connect digital data. The Sound Blaster-compatible Game/MIDI port uses TTL levels, just like the classic parallel printer port. No one cared about ground loops when connecting parallel printers (at least as long as the printer and the computer are connected to the same mains circuit), and the SounndBlaster-like MIDI connection is not more sensitive either.

Optical isolation might be a really good idea, if you do not only connect the MIDI ports, but you send the audio data back to the MIDI transmitter through an analog audio connection, though.