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Input selector for SPDIF inputs

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I don't know whether this has been asked before, but it'll be strange if it hasn't.

I am thinking of designing (or even buying off the shelf) a simple 3-way or 4-way relay based input selector module and using it for selecting from 3 or 4 digital SPDIF inputs, and then feed the selected output to a DAC.

I intend to mount the input selector board really close to the rear panel, and then the DAC within a few inches of the input selector board's output. The RCA sockets will be panel mount types, and I'll have a few inches of cabling from those sockets to the inputs of the relay board.

The relay board will not have any active or passive component in the signal path, other than the relays.

I intend to use a DPST or DPDT relay for each SPDIF input, so that I can switch both the ground line and the signal line.

  • Will this work? Do you see any problems?
  • If I use the Toslink modules from Twisted Pear, can I wire one Toslink module's output signals in parallel with the wires from an RCA socket, so that a user can choose whether he wants optical or coax digital for each input? No switches to select between Toslink and coax -- just hard-wired in parallel. Will this work?
 
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I think mechanical relays are not the most suitable for high speed digital signals.

For your input circuit build something like this:
(please note that the shown MAX3280 should be better replaced by a 26LV32)
1k0.jpg


After the individual inputs use a 74xxx series digital ports to enable / disable each input.
An "AND" port would be an easy implementation but please realize all signals here are 3,3V (not 5V as common TTL is)
 
This is what our 4:1 Mux/Demux module does. No relays.



4:1 Mux/Demux Switching Module
Yes, I'd asked you about these a few years ago and you had explained. I was wondering whether I can build a relay based switching board. I was also thinking of more than 4 digital inputs. 4 digital inputs seems like it's more than enough for any normal household, but the split between optical and coax seems to cause problems for many of my friends. They always complain that they either have too few optical or too few coax inputs in their DAC or amp.

That's why my exploration started with the thought: can I have effectively just 4 inputs but support both coax and optical for each input, so that some people may use most of their optical inputs and others may use most of their coax?

Can I use your 4-way board and still somehow connect both optical and coax to each of the ways? Can I use a simple DPST switch at each input on the rear panel, for instance, and "up" will mean coax and "down" will mean optical?
 
On second thought, DPST does not seem like a good idea -- will DPDT work?

Due to some strange coincidence, when I looked for DPDT toggle switches with
  • panel mount
  • gold plated contacts
  • flatted lever
  • ON-ON actuation
I get only one choice from both Mouser and Digikey: this NKK switch

I didn't realise this was such a unique combo of features. Expensive.

What are B1 to B4 on the silkscreen image of the 4:1 switching module?
 
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