I owned a CT1750 in the 1990s with attached Wavetable daughterboard.
I experienced also the lack of midi music when I had my flightstick attached to the gameport. It took me some time to figure out that the attached joystick was the root cause of the missing midi music.
So at least for the CT1750 this phenomena is well known. I don't know if later versions of SB16 were fixed.

moturimi1 wrote on 2026-01-27, 14:51:

I owned a CT1750 in the 1990s with attached Wavetable daughterboard.
I experienced also the lack of midi music when I had my flightstick attached to the gameport. It took me some time to figure out that the attached joystick was the root cause of the missing midi music.
So at least for the CT1750 this phenomena is well known. I don't know if later versions of SB16 were fixed.

Yeah it has a very similar design and some versions share the same DSP (4.11 like mine)... Interesting!

I did try a few gamepads in my first tests, but all three were Gravis Gamepad (classic) models. I pulled out a few more controllers today, and everything works properly when using a Gravis GamePad Pro or a no‑name gamepad.

First time I’ve ever encountered that kind of problem with any of the 10+ Sound Blaster cards I’ve owned, or the bazillion Gravis gamepads I’ve used over the years.

Perhaps the 5V supply at the joystick port is insufficient to drive the transistors in the gamepad and the optoisolators in the midi adapter at the same time?

I think you'd need a scope on pins 12 and 13 of the joystick port to see what is happening to the MIDI signal lines when the gamepad is connected

NeoG_ wrote on 2026-01-28, 01:14:

I think you'd need a scope on pins 12 and 13 of the joystick port to see what is happening to the MIDI signal lines when the gamepad is connected

You mean pins 12 and 15?

Linoleum wrote on 2026-01-28, 02:47:

You mean pins 12 and 15? https://fc09.deviantart.net/fs70/f/2014/243/8/e/computer_midi_game_port_by_mad_king_corduroy-d7xfbct.gi […]
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You mean pins 12 and 15?

Yes, apologies it was a typo

maxtherabbit wrote on 2026-01-28, 01:11:

Perhaps the 5V supply at the joystick port is insufficient to drive the transistors in the gamepad and the optoisolators in the midi adapter at the same time?

Somehow, gamepads are making the big difference, so first checked there. I noticed a huge difference between Classic Gravis Gamepads and the other between pins 5 (ground) and 8 (5v). I measured a 12k resistance on the Classic Gravis Gamepad and between 1k-4k for the other gamepads.