SPDIF questions

[harry66]

Hi,

I bought myself one of the nice Tinker Board S to use it with Volumio and intentionally with the S/PDIF output.
As S/PDIF is not "plug in"-ready  on the board, I started some research on the matter to build myself the needed connection peripherals.
S/PDIF by its nature is a HF signal and needs to be treated carefully to not introduce unwanted disturbance on the line.

My research led to these questions:

1. I need a schematic to see if a coupling network is already integrated to connect a RCA. If it is a TTL signal, connecting it to a S/PDIF sink can go horribly wrong.
   
2. The signal uses a HF carrier of several MHz. For this reason proper grounding is essential: What about the "PWM" pad close to S/PDIF? It was said this pad was GND. That true? So again schematic
   

The schematic I found on the net is incomplete as it does not show some essential parts of the board.

Somebody to help out?

BR
Uwe