S/PDIF transmission with RS422/485 tranceiver over twisted pair with SN75176

[emuman100]

Guys,

I have done it! I got the idea from a web site that I forget the URL too. I built some conversion circuits, toslink and coax to TTL, which I fed into an SN75176. It was fed over twisted pair telephone wire using RJ-11 jacks and connectors to interconnect. At 10ft, the sound is perfect. The receiver circuit has an SN75176, it's received output connects to a circuit with converts TTL to coax, which then is fed into jwb's DAC. With a good tranceiver (I'm getting SP1485ECP which operates up to 20Mbps on Monday) reflection and jitter is minimized, and allows transmission of S/PDIF over thousands of feet with no noise or degradation. At work, we have over a mile of cable run that transmits data at 9600bps. Even though S/PDIF uses much faster transmission rates, I am almost positive it will work well. Why hasn't this method of transmission been used? I think it works pretty damn well.

[emuman100]

No replies? I'm sure someone would have found some sort of error with it. Anyone have any input? I had the circuit running pretty much all day and jwb's DAC is still sounding good. The transmitting IC gets slightly warm, but still pretty much perfect operation. I'm looking fot your input because I'm a new commer to S/PDIF transmission, and don't really know much about it.

[rfbrw]

If you are happy with it and it works well, why worry about what anyone else thinks?

[emuman100]

Well, I'm just wondering if anyone else did it. It works too well to be as simple as soldering in an 8 pin DIP socket and connecting lines to it, then connecting it to a transmission line. Because of it's operation, I'm wondering why no one ever tried this before.

[rfbrw]

I once wanted to stick a CD player on a BTS router and I stuck a 75176 in a Technics player drove drove a 100ft drum of coax. With a Prismsound DSA-1 on the other end, doing the testing, there were no problems. The chief engineer wasn't too keen on them though, he felt they died too easily.

[emuman100]

Really? Odd. For the life of me I can't kill one. At work we use them for long distance serial transmission, and they get lightning transients and high voltage spikes, shorts, ESD, and even with atleast 8 years of operation, I never had one die. They seem quite resilliant to me. I can probably go thousands of feet and still get good transmission. I think everyone should use them.

[dhaen]

Modern Rs422 tranceivers are slew rate limited, and will not be able to transmit even the fundamenal.
Twisted pair is used for a similar audio standard described in AES / EBU spec's. This runs for "miles" though proper cable, and quite a distance through "improper cable" (RS422)

[rfbrw]

Originally posted by dhaen
Modern Rs422 tranceivers are slew rate limited, and will not be able to transmit even the fundamenal.
Twisted pair is used for a similar audio standard described in AES / EBU spec's. This runs for "miles" though proper cable, and quite a distance through "improper cable" (RS422)

I once worked at place that needed to move audio around the building in the days when your choice of AES rx was the BBC AESIC or some unobtainable Sony device. Proper AES/EBU spec cable was used and the stuff was hideous. Halfway through the building A4 size eq/boosters had to added. In contrast the 270MHz SDI over coax was a breeze.

[Ouroboros]

Not all RS485 drivers are slew-rate limited. Have a look on the Maxim site for parts with digital pre-emphasis for high bit-rates over fairly long cables.

It is certainly possible to carry SPDIF over CAT5 twisted pair for 100 metres. (As a comparison I am running 2.048M bits/sec over a single CAT5 pair here at work over 500 metres, although I am using a simple first-order C-R equaliser at the receiver).

[Jocko Homo]

With a good tranceiver (I'm getting SP1485ECP which operates up to 20Mbps on Monday) reflection and jitter is minimized.

And you can prove this I suppose?????

Hard to convince me that anything with Schmitt trigger inputs will have low reflections.

Jocko