DS Mod question: replace XLR or coax input with another Toslink?

Hi @tedsmith

This is way out there, and I would understand if it doesn’t get a response.

I love the performance of Toslink on my DS DAC, and as per your advice I love it most when there are no other noise-conducting cables connected to the machine. The problem is that I have two sources and there’s only one Toslink input.

I’ve yet to find an external Toslink switch which actually functions at 192kHz sample rates. I know that I can get Toslink-to-coax converters and run one of my sources that way, but that’s adding a crappy external power supply and a potential source of electrical noise to the system.

So I’m wondering whether it’s feasible to mod the DAC, removing the XLR or coax input and adding another Toslink one. The second input is just for my TV so it never goes above 48kHz, meaning I could use a standard Toshiba TORX177 or 147 receiver component if a suitable Vcc is available and if the output from the component is compatible with the circuit to the FPGA.

Electronically, is this feasible?

Edit: perhaps I could turn the coax input into a combo like many other products do, with the new optical receiver’s output soldered directly to the coax input’s signal pin.

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I was going to recommend your suggestion. A TOSLink receiver only needs 3.3V to 5V, Gnd and outputs about 0 to 3.3V (or 5V) You’d want to use a voltage divider to, say, lower the voltage to 0 to 0.5 volts. If you aren’t using one of your I2S outputs you could get 5V from the HDMI connector, use a TOSLink receiver that’s happy with 5V and then divide the output by 10.

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That’s incredibly helpful, thank you! It’s inspired a followup idea…

If 5V is available from the HDMI connector, then I could use that as a power supply for an external Toslink to coax converter that hangs directly off the RCA connector! I get a very clean supply, no ground loops, Toslink’s advantages over the distance to the source and a DAC that retains its resale value.

0.5V is what’s needed on the coax input, you say?

Edit… maybe external is what you meant in the first place. When I first read your reply I was thinking about cutting a hole in the backplate and soldering a line from the 5V supply. Took me a while to imagine that being all external and it seemed like my own idea. Re-reading you, maybe I was just slow on the uptake :slight_smile:

A couple connectors and you can have your own wart :slight_smile: