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TOSLINK/SPDIF output board (project)

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Twin TOSLINK plus coax output board.


Transformer isolated coax output based on Sony MDS-E10 ‘pro’ output stage. The pulse transformer is the most expensive part by far (about 4GBP) but the PCB is padded out for a couple of options to mitigate against availability issues. 


This project is partially @BearBoy’s fault 😆👍

I subsequently found the part Sony use for the Coax RCA connector so I will redesign the PCB. I also missed one capacitor in the coax circuit. No real consequence but I’m a stickler for detail…


I originally designed this for my MXD-D4 to provide TOSLINK output from both the CD and MD sections. However with @BearBoy’s input I added the coax output and selection jumpers so it can be used with an MD-only machine and thus add twin TOSLINK and coax outputs.


Just a DIP 74HCU04 IC goes in the socket. 



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It has to wire into a couple of points on the main PCB (or stuffed into the ribbon cable socket before @sfbp pulls me up on that one!). The machine doesn’t need to have any digital I/O on the back panel already. 


I’m only really familiar with the Sony machines and it should work with any as they use the SPDIF protocol natively internally. Otherwise this PCB has the interface drive circuits so doesn’t rely on the main board having any digital outputs already. 

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11 hours ago, BearBoy said:

Wow. That looks like a cracking piece of work, @kgallen. Really professional looking.


Will that work on any Sony deck with a single digital output?


And apologies if I was responsible for sending you down this particular rabbit hole 😲  😆


I think I may be the one that (indirectly) caused this. I am the proud possessor of its previous incarnation which is a simple 1->2 Toslink splitter, designed and built by Kevin.

The idea of adding the direct (coax) out is great, too. But I am happy with my gizmo regardless.

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Sorry I didn't realise the photos were so big - shrunk them now I've managed to get on the site via a PC and Firefox (rather than on a phone).


7 hours ago, sfbp said:

I think I may be the one that (indirectly) caused this. I am the proud possessor of its previous incarnation which is a simple 1->2 Toslink splitter

Indeed Stephen, that was the first project that made me dig into the TOSLINK circuits. This new project was originally pretty much that splitter without the input receiver and wired into the machine, but then @BearBoy and myself started discussing a coax output, so I looked into that and added one.


45 minutes ago, Richard said:

This looks fantastic Kevin - really neat! I wonder what the chances are of somehow being able to retrofit one of these into one of the Onkyo Hi-MD decks maybe 🤔

I'm not happy with the coax RCA socket on this v1 PCB since it doesn't have any mechanical support. The one Sony use has a screw that can be used to secure it to the case for mechanical support. The one I have used relies on the solder joints to the PCB (although I did pad out a large area of copper for mechanical support). Subsequent to sending off the PCB design for manufacture, I finally tracked down the part that Sony use (attached) and found someone on eBay selling some, albeit with the black insulator rather than the usual gold/orange for SPDIF. None of the mainstream suppliers here (RS, CPC, Farnell) stock this component. I think Mouser might list the range but I didn't want to buy a thousand or have one shipped from the US at great expense. Anyway I'm in the process of redesigning the PCB for that (larger) part, but I haven't fully tested this v1 design yet, so won't order a v2 design until that's complete.


Regardless, this board could actually be used sub-equipped as a single or dual TOSLINK output, and as long as your machine has SPDIF internally (which it will if it uses the Sony CXD DSP chips) and 0V and +5V then it can be fitted. The electronics is easy, it's the taking apart and drilling the back panel which is the hardest part.


I have some spare v1 bare PCBs if anyone wants one to play with. I'll let you know how I get on with the v2 and if anyone is interested, give me a shout. You lot might get a little prezzie anyway for your ongoing help and encouragement!


I suppose what I should do is do an "all features" PCB that can be a splitter or fitted internally to a machine with whatever combination of TOSLINK/Coax outputs you want. I guess this could end up being a bit over-engineered because the splitter needs a power supply and an input circuit whereas the output board doesn't require either.


However I guess the point is I know about all of the building blocks so if you fancy something, drops some ideas around. After all these little projects come about from suggestions/ideas/threads on here! 🙂


Boy, it's great to be back...


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