Adding RCA SPDIF Output To Khadas Vim3l GPIO Pins?

[Tony D.]

I am adding a SPDIF RCA output on the GPIO pins of my Khadas Vim3l SBC and I would like to know how close the RCA should be soldered to the pins? Should I solder the RCA directly to the pins or is a short flying lead okay?

Thanks for any info.

 

[Markw4]

You should use a connector to connect to the pins. Best not to solder to them. A proper SPDIF cable is a 75-ohm transmission line. If its a good one it can be moderately long, however clock timing jitter may get worse with longer length. Best to keep it as short as reasonably possible.

 

[nattawa]

there are generally two ways of doing anything, 1) doing it the right way, or, 2) hack it and see if we can get away, if negative then consider 1.

to answer the question, since the wiring from the gpio pin to your rca cable/jack is most likely in no way any near the length of the rca cable itself, its length doesn't really matter.

The attached would be a proper way of doing it, in case the hack job fails, or somewhat works but fails at higher sample rate and resolution. Buffer the gpio with a logic buffer, provide with back-end termination (R4-R13) so that the transmission line is properly terminated - loaded or not, provide with chassis isolation with a transformer. This circuit has been proven working well up to 24bit/192KHz, even with a cheap, dodgy PE65612 transformer that is not specified for such data rate. It can be constructed on a small perfboard.

 

[Tony D.]

Thanks for the replies. After trying everything I could to make this work, and unsatisfactory results I've decided to buy a Raspberry Pi 4B and use the USB output on the Pi into a SMSL PO100AK DAC (which I already have) to output audio over SPDIF. The SMSL will output into my MiniDSP 8x12DL and all will be installed in my car.