The MediaVision ProAudioSpectrum16 uses -5v, too.
MediaVision - PAS16? - Help ID the card - Help with drivers
However, the actual power the PAS16 uses isn't much.
It merely needs the negative voltage for the opamp.
The principle itself needs the negative voltage.
In theory, the solution to the problem is very simple.
If you have a cheap sound card (not the precious PAS16) that needs a the negative voltage,
just mount a -5v voltage regulator (with its basic support parts) to the card and use the -12v line as a power source.
Also consider a little cooler, just for the sake of it. Better safe than sorry.
Alternatively, have a look at this thing:
https://www.philscomputerlab.com/voltage-blaster--5v.html
It's essentially the same basic amateurish idea.
Just in commercial form, lacking a fuse, diode and a power LED.
If it was me, I would take the opportunity to make this a DC cleaner card, too.
Adding some filter caps for the other voltage rails.
Or at least add the usual 100nF/1µF/10µF caps, to filter out RF/harmonics.
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