Oh, that's simple (in theory). Just get a datasheet of the DAC and follow the traces. 😉
If you have got an ohm meter or a multi meter, you can also check which trace or wire has contact with the IC's power pin.
Normally, red an black should be for plus and minus. And yellow/green for the amp/speaker part.
But I'm speaking under correction. I don't own a Speech Thing myself and so this just pure guessing.
So it's probably better to wait until a Speech Thing owner will answer you question.
And I also think it's better to try with passive head phones first, before connecting a speaker or an amp - sometimes the power of such a DAC is sufficient to drive sensitive head phones (depending on the impedance and other factors of the DAC and the head phones).

Good luck! 😀

there is more to it in the Disney Sound Source speaker part as it is self-powered with a 9v battery:

I'd say your best bet is to use a multimeter to isolate the 5v wire and not use it at all. Then attach a passive speaker/headphones and try to find the pair that carries the audio. If you need to build an amp then use an external power source like the original design, over-drawing current from the LPT is not a good idea...

The whole Sound Source, parallel port dongle and speaker, is powered by the battery. The four lines represent power, GND, audio out and status LED. The parallel port was not intended to provide a source of current. The schematic in the Sound Source Programmer's Guide would confirm this. One thing the schematic does not tell you is whether the power to the IC is +5v or +9v.

Rail voltage should be discernible by pulling a spec sheet for the IC, so that shouldn't pose a challenge.

Thanks for the info everyone!, i can't find the datasheet, probably because is some random custom part from that time, i did found the programmer guide, that says that there are 4 pins in the cable and gave me the same info that keropi said, power, gnd, sound and "Power Control" that turns on the amplifier.

keropi wrote:

there is more to it in the Disney Sound Source speaker part as it is self-powered with a 9v battery: […]
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there is more to it in the Disney Sound Source speaker part as it is self-powered with a 9v battery:

I'd say your best bet is to use a multimeter to isolate the 5v wire and not use it at all. Then attach a passive speaker/headphones and try to find the pair that carries the audio. If you need to build an amp then use an external power source like the original design, over-drawing current from the LPT is not a good idea...

I think i can do something with the photos! thanks!

I got it working! really nice, thanks for the info guys.