Is it possible to take the signal before optical for a coaxial digital connection? - diyAudio
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Old 25th September 2013, 10:46 AM   #1
Nazo is offline Nazo  United States
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Join Date: Nov 2010
Location: Alabama
Default Is it possible to take the signal before optical for a coaxial digital connection?

So I'm thinking of building a project where I would have a cheap USB DAC connected to a Fiio D3 to act as the actual DAC with a CMoy handling the analog stage. While it may be no substitute for the $200+ DAC+amps out there, it's pretty darned good in my initial tests. One piece of inelegance is very annoying though: connecting the USB DAC to the D3. Running a huge optical cable from one to the other and then having to switch them back and forth (or using a Y-splitter) isn't just ugly and messy, but it actually gets in the way and makes the whole package bigger and less portable.

I'm wondering: is it possible at all that the digital signal going to the optical converter is basically the same as what is used with coaxial connectors? Or, if not, could it be something simple like adding a resistor or capacitor or other such thing? If I could just run a couple of wires from it to the D3's coaxial input, I could have it completely internalized. It might be bad to have both the USB DAC and something else connected to that input at the same time, but I can't foresee having the USB connected AND an active coaxial connection at the same time.

Is it possible, or are they two very different things in this case?

I've attached a picture of the PCB from the USB DAC in case it helps determine anything. I circled the three pins that I believe go to the optical section of the TRS connector.
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Old 26th September 2013, 11:06 AM   #2
atupi is offline atupi  Romania
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My Egreat media player has only optical digital output and i obtained a spdif connection installing a RCA connector between GND and Signal of optical connector. Works very well for me. I have already a coupling cap on my DAC spdif input.
You can follow same way for your situation and it should work.

Adrian
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Old 27th September 2013, 06:02 AM   #3
Nazo is offline Nazo  United States
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Join Date: Nov 2010
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Ok, after a LOT of digging around and confusion since I've never done anything remotely like this I managed to find a data sheet for the VT1620A and figure out which pin of the three is the signal. In fact, it explicitly states "SPDIFO" for pin 28 in the datasheet. After following the trace, failing, and using a multimeter and a magnifier and a very very steady hand, I managed to identify connector 3 (the bottom one) as being the SPDIF signal and soldered in a connector with RCA on the other end. After not so bravely forcing myself to flip the switch, it worked. No smoke, just clear clean audio.

Thanks. I am curious, is there any danger if there were two SPDIF signals connected at once to either the USB DAC or the D3? I seriously doubt I'll ever have both at once, but I'd like to at least hear that the whole thing won't go up in flames if I did accidentally do it...
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