AY-3-8910 sound card for ZX Spectrum 48K

I have no idea, It is a 2 layer PCB with nothing special on it. Are you sure you did not select any extra features like gold plating or chamfered edges?

Yes, you need games that utilize the AY chip, most of the 48K games use the beeper, because the original Spectrum 48K did not have an AY chip. Then came the Spectrum 128K, which had an AY-3-8912 in it, so the game developers quickly started supporting it. Unfortunately not all of these games fit in 48K memory, or even if they did fit, they contained routines that detect the machine type, and if the detection said 48K, the AY sound routines were not used. The list I provided is the most complete one I have seen out there, although all the games on this list work well with a 48K Spectrum with an AY attachment, there are now more software that is not included in there because the list is not updated very well. I don't have a schematic to share because I use an old CAD software that doesn't have a schematic to PCB layout feature. So I jot my schematics on paper, and draw the boards manually from there.

All the 128K models have their AY chips from factory, they don't need this. This is only for the 48K models.

The 128k +3 has a poor AY and you have to modify the board so I thought you could use this instead.

I understand your logic, but AFAIK, +3 expansion port is NOT compatible with the 48K so most probably it will not work and may even crash the computer. This board is exclusively for the issue 2 to issue 6 48K Spectrums. May work on a 128K Toastrack and 128K +2 Grey, if their on-board AY-3-8912 is faulty and removed.