[sdiy] S/PDIF cable.

[Batz Goodfortune]

Y-ellow All.
         And thanks to everyone for that. Yeah. Sounds like 75ohm coax is 
the go here. I was kinda hoping the 50 would have been suitable simply 
because it's a narrower diameter but it really isn't overly traumatic. I'm 
not exactly spoilt for choice at the moment.

At 09:01 AM 4/27/02 -0700, John L Marshall wrote:
>Use the 75 ohm coaxial. Do you have RG-59 foam? That would be my first
>choice.

I always thought RG59 was thinner than this stuff but I don't have much 
choice. The sample I have here doesn't have anything printed on it so it's 
unclear what it is. But it IS 75ohm. It's actually designed as aerial cable 
but it works OK for video. I have surveillance cameras running on 20 metres 
of the stuff with out any problems.

>Transformers exist to convert from AES/EBU 110 ohm balanced to 75 ohm
>unbalanced. The unbalanced lines can run long distances.

The problem at that end is that the only option on a Yamaha O1V is a 
4in/4out AES/EBU podule. I'm not even 100% sure it won't spit the dummy but 
since S/PDIF is a superset of AES/EBU (logically) and none of the 
extraneous bits will be sent anyway, it should work. And Biphase mark 
doesn't require polarity concerns unless of course there's some 
non-isolated electrical imperative. Which of course, the transformers take 
care of.

The podule has 8 tiny transformers on it, to, as you say, convert balanced 
to unbalanced. But these seem to be entirely isolated at the back end from 
everything so I should be able to connect the coax across the trannies 
ignoring the centre tap and that should work. I hope! The centre taps seem 
to be common grounded so it would be a good idea to leave those alone.

Some of the sources have transformers but the RCA sockets are still 
grounded. Makes no sense to me but there you go. But one in particular has 
no isolation at all so I'll be relying entirely on the transformer in the 
back of the podule for that. The podule apparently takes care of 
synchronization so I don't have to worry about a central word clock 
generator. I have assurances from the supplier but Yamaha's documentation 
is less than clear. They'll hear me shouting abuse at them all the way over 
in Japan if this is not the case.

Believe it or not it's taken me 2 years to get to this stage. I remember 
discussing how to make a suitable transformer should I need to with Peter 
Ullrich just prior to having to leave the list. Hello Peter if you're out 
there. But it actually took them this long to get back to me with assurance 
that it will handle asynchronous inputs.

The only other problem I've just realized. The I/O on the back of this 
podule is actually a DB25. That's going to be a fiddley cow of a thing to 
hook coax to. Still, we have to do what we have to do. And I've had to do 
worse. And if it really is unworkable, I guess it wouldn't hurt to run a 
short length of some liter shielded cable out to an RCA socket. Or 
something along those lines.

Anyway thanks all for that. Sounds like a plan.

Be absolutely Icebox.

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