That's one weird card. I'd tend more towards prototype than hobbyist stuff - the main chip on the daughterboard is an NE558, a quad timer usually associated with the game port. There doesn't seem to be one on the main card, but that game port looks completely by design. What puzzles me are those two push-buttons. Is there any kind of legend suggesting what they do? Apart form them the card looks like a pretty regular ES688 card in terms of components, if not how they are placed/hooked up.

Does the card work?

the push buttons seem to be labeled BASS and TREBLE , TDA1524 is a volume/tone control IC so probably these buttons activate bass/treble boost
and that addon board is connected to the joystick pins of ESS688 so it is just the missing stuff for it
now why this exist is another story - perhaps someone made a run and then found out the joystick is actually missing parts and created this parasitic pcb to complete it ...
it looks horrible as a product to sell 🤣

It is a version V2.3 card. So it is unlikely that they discovered such a large bug.

It's already quite clear in this thread that the add-on board is a game port implementation. It takes the game port chip select from the ESS688, it contains the NE558 timer chip required for a complete 2-joystick game port and the LS244 bus driver chip to send the data obtained from the game port to the ISA bus. As the card is labelled "REV 2.3" and there are no traces of game port stuff on the card, it looks like the designers of the card decided to just provide the MIDI interface on the game port, and later on someone decided that having a fully functional joystick interface on the card would be a good idea, so they bodged it on.

Game Ports on multi I/O-cards were quite common, even when not everyone had a sound card, so game ports on sound cards always looked a bit superflous to me. Of course it makes sense that both the sound capabilities and the joystick interface help gaming, so a grouping these features on a "improve your game experience" card makes some sense. Nevertheless, why add a game port on PCs that already have one. It seems later / cheaper multi-I/O cards cheaped out on the game port and substituted the dual-joystick (4-axis) port by a simpler single-joystick (2-axis) port using a NE556 instead of a NE558. The move from fully-featured game ports to crippled game ports on multi-I/O cards might have been a motivation to retroactively add a game port to this sound card design.

Thanks for the replies (just as a little precaution - my knowledge about sound cards is rudimentary at best). I add an image of the backside of the card for completeness to see what all those wires do. I was looking through ESS soundcard images online, but I could not find any specific model with those treble and bass push buttons (how would you adjust treble and bass with a push button anyway ?) So assuming the daughter board and all the added wires and modifications are solely concerned with the gameport - how would I get the Sound card side running under pure dos? Do I need an install disk or can I just set variables like with a normal SB pro card ? Is there any additional softare for these cards like mixer etc.

(about testing that gameport - I currently dont have a pure DOS joystick. I recently bought one thats supposed to work on Winn95 and DOS but it was not working under pure DOS. I am currently looking for another pure DOS one. Then I may have a look at that as well.)

Grab these utils to help you with joystick testing.

Re: Good DOS joystick test program?

Aui wrote on 2025-03-09, 23:09:

So assuming the daughter board and all the added wires and modifications are solely concerned with the gameport - how would I get the Sound card side running under pure dos? Do I need an install disk or can I just set variables like with a normal SB pro card ?

Just like an SB pro, setting jumpers and BLASTER is fine to get the card working, but you might want to set the mixer volume on boot. IIRC the utility for that is called ESSVOL.EXE.

Aui wrote on 2025-03-09, 23:09:

how would I get the Sound card side running under pure dos? Do I need an install disk or can I just set variables like with a normal SB pro card ? Is there any additional softare for these cards like mixer etc.

No special software necessary - just set the jumpers, and:

set BLASTER=A220 I5 D1 T4

If you use Mpxplay, set the following instead:

set BLASTER=A220 I5 D1 T4 H0

...it makes Mpxplay to use ESS native mode, instead of just SB Pro.

There is some software for ES488 and ES688, including the DOS mixer for ES688:
Re: 12-bit sound card

Ok - sound side of things is working great !.
Now I need a joystick for further testing ...
I will report back later....