Maximum length for Digital Coax (or Toslink)?

[Toussaint1800]

Help! Cable experts, I have a cable question! Can anyone tell me what is the maximum length of digital coax (or Toslink) cable? I want to link two AV receivers together and the two units are separated by 25 meters (82 feet). If anyone can provide a web page link to an "official" source, I would be grateful! Thanks!

[Aussie Geoff]

Hi,

Try this LINK. Two quotes:

Coaxial S/PDIF connections work typically at least to 10-15 meter distances with good 75 ohm coaxial cable.

Because high light signal attenuation in the Toslink fiberoptic cable, the transmission distance available using this technique is less than 10 meters (with some equipments only few meters).

Geoff

[Airplay355]

how come you are linking two receivers together? and why with a digital cable?

[Toussaint1800]

I've included a JPG file here that shows a sketch of what I want to do. As the graphic shows, I've got a Home Theater receiver on the top floor of a house, and another HT receiver on the ground floor. I want the ground floor receiver to "see" the top floor receiver as a digital input - in other words, I want to listen to the music output from the top floor receiver via the receiver on the ground floor. The distance from the digital output of the top floor receiver to the digital input of the ground floor receiver is approx 25 meters (82 feet). I believe a cable run of 25 meters is too long for digital optical cable (Toslink), so I'm thinking digital coax is the right way to go. Does anyone think that 25 meters is too long for S/PDIF digital coax cable? Is it necessary to amplify the digital signal along the way? (is a "repeater" necessary?) Many thanks for your opinions and advice, cable experts! -- Toussaint

[Aussie Geoff]

Tousant1800,

I see that you are trying to do...

Clearly the run length you are planning is at the outer limit of the SPDIF specifications - so some hardware will work with it and others not. Also you will not be able to use any specialist high quality cable (too expensive). I recommend that you get your cable intallation people to make a up a 25m length of reasonable quality 75 Ohm (Beldin etc) cable and try it with your recievers before you run it though the house (save money if it doesn't work) as I am not aware of any domestic extenders etc for SPDIF links...

As an alternative there are a number of products that broadcast the digital signal over an 802.11G Wireless network... and you can get recievers at the other end... However this technology can be a little complex to set-up...

Geoff

[Toussaint1800]

Hi Geoff - thanks for that reply. I've been shopping around the web and I found a cable company based in Spokane, Washington that proposes custom length SPDF digital coax cable : (http://www.cobaltcable.com/product/index.htm). 100 feet of SPDIF digital coax costs $258. But it would be a shame to spend the money and later discover that it doesn't work. About that wireless configuration you mentioned -- would that transmit a digital signal point to point? Can you tell me who manufactures these products? I was thinking about avoiding a wireless solution because I'm afraid of line interference, but I could easily be wrong - I'm a newbie to this stuff!

[Toussaint1800]

Geoff - By the way, I forgot to mention that I've already tested the link between the two HT recievers with both SPDIF digital coax and SPDIF toslink cables. The cable length tested in both instances = 30ft (9.14m).

The two systems were in separate rooms, and the sound from both systems was crystal, really good quality (in my humble opinion). According to my (simple) reasoning, I'm just trying to multiply that cable length by 3. I'm thinking : Surely a digital audio signal should be able to travel that far, right? Wrong? Hmmmm ... not sure ...

[Aussie Geoff]

Toussant1800,

I've just checked the specs for three wireless digital transmitters and while they all have TOS Link and Coax SPDIF interfaces they only support MP3 and WAV style files (CDs) not DD or DTS - so this leaves the cable as the likely best choice...

I guess you are going to have to take a punt and order the cable - the fact that you have got 10M to work is a good start... I'd definely get Coax... Good luck!

Geoff

[brucek]

100 feet of SPDIF digital coax costs $258

That's fairly expensive. I would suggest you use 75 ohm quad shield RG-6 instead. A lot cheaper and very effective. It has a bandwidth that far exceeds SPDIF digital signals.

Radio Shack sells this in pre-made lengths of 100 feet terminated with F-Connectors - used generally for satellite instalations.

You can purchase very nice adapters to convert to RCA connectors. The adapters in gold are $4.29 and 100 feet of terminated RG-6 is between $35 and $45 dollars.

Here's the adapter:

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=278-290

Here's the cable:

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-1559

:roll:

brucek

[ekkoville]

Hey Bruce, the plugs you show look like regular RCA connectors, would two cables and connectors work the same hooked up to analog outs/ins? Or would the signal be compramised? Cambridge Soundworks here in New England makes custom runs of cable with 75 Ohm coax for their installs, but I wonder if you can use the RG6 for analog.

Erik

[Toussaint1800]

Bruce - Thanks very much for that. Interesting. So, if I understand correctly, you're saying that this "75 ohm quad shield RG-6" cable will carry the SPDIF signal a hundred feet or so, and I would just need those RCA plug adapters on each end to connect the cable to each receiver? Interesting. I wonder if anyone has actually tried that and got it to work? I'll have to try it.

In my research, I found this website : http://www.epanorama.net/documents/audio/spdif.html

"S/PDIF ( IEC-958 ) uses 75 ohm coaxial cable and RCA connectors. 75 ohm coaxial cable is inexpensive, because it is the same cable as used in video transmission (you can buy a video cable with RCA connectors to connect you S/PDIF equipments together). Coaxial S/PDIF connections work typically at least to 10-15 meter distances with good 75 ohm coaxial cable".

Also this note :

http://www.rane.com/note149.html

Containing a table which "summarizes the differences in the electrical characteristics of AES3 and S/PDIF interfaces". In this table, the author claims that S/PDIF experiences "signal loss driving long cables" and is limited to 10 meters.

I wondered : The S/PDIF specification is two things : a data protocol and a physical transport (a cable), right? So where does this "10 meter" limitation come from, anyway : the protocol or the transport? Maybe that's a dumb question, I don't know ...

[Chris D]

FYI, I use RG-6 Quad Shield cable in my walls to pass audio signals. I use connectors that I bought from Parts Express (see the link at the top of the page) that crimps on RCA connectors straight to the RG-6 cable, so I'm making my own cables. No adapters necessary, and it works fine. I'm currently using it as subwoofer cables through the walls in my theater.

[ajpoe]

If you are only listening to music, then have you considered just running analog cables from the source to the second receiver? I just did this same thing for my HTPC since it's my music server. I had speaker wires already run to my bedroom from a previous zone 2 setup. I turned those speaker wires into RCAs. From my soundcard, I run the digital out to my DAC1 in the main room and the new RCAs from the analog out to my bedroom receiver. I like this setup much better than a zone 2 setup because I now have full control in the bedroom with its own remote and the main processor doesn't have to be powered on for zone 2. I would think analog cables would carry a signal further than a digital coax without issues, but I'm not an expert in this area either. I just know it works great for me... I would say my run is at least 60-80 feet and I still have crystal clear sound in my bedroom.

AJ

[aaron]

Gents.

I ran quad shielded RG-6 75 ohm cable from my PC to my home theater recently when I put on my addition and used those RCA adaptors Bruce pictured. The run connects my soundcard's digital output to my Preamp and the PC serves up a vast MP3 collection for summer parties outside (zone 2). I don't recall the exact footage I ran, but based on my home dimensions, it has got to be somewhere around 60 + feet. I never had any problems.

I did use very good quality quad cable.

I suggest you simply visit your local radio shack and buy that 100 foot roll of pre-teminated coax with a pair of those adaptors. Put the receivers in one room and hook them up. If it works you're golden. If not, return it. Just don't lose your slip.

[ajpoe]

Just some FYI since I had to get some for my satellite run. Parts Express has pre-terminated RG-6 cable on clearance. A 25' cable with F connectors is $1.80 and a 75' cable with F connectors is $4.80. It might save you some money to get it from them if you plan on going that route.

75'
25'

AJ

[Meat_PoPs]

I've made >50foot spdif runs on dollar store grade rca's without any audible signal degredation. This is strung side by side with analog cables, power cables, near flourescant and incadescent lighting, and not so much as a crackle or pop. Using three dollar store 18foot rca's strung with dollar store female-female adapters.

If you use high quality cables and the equipement you're using has good termination / transmission properties, I can't see having any problems getting well over your attempt.

I was using a harmon/kardon avr300 receiver for reception, and an nvidia nforce mcp-t based motherboard in my computer for transmission.

[Meat_PoPs]

Warning: Off topic.
You guys seem to be in the know about proper cabling. What's the proper way to ground 75ohm coax from an antenna? I just went to hook up a run from my massive rugged area antenna (picks up fm stations out of province woohoo) and the bastage threw sparks! The tower it's on is grounded with an 8' ground spike so thats taken care of but the antenna definitely isn't.

[brucek]

You've demonstrated the importance of grounding antennas and how a potential can build up on the ground lead. You can imagine how bad the ground loop you would have created with this situation.

You need to do two things.

First you have to run your antenna coax lead through a grounding block that is mounted outside before the lead enters the house. If you can't find a sheltered spot to mount it, they have rubber boots that fit over the termination ends of the leads to keep the moisture out. The blocks are inexpensive and found at Radio Shack.

http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=15-909

The grounding block is grounded with heavy cable to the outside grounding rod that the tower uses.

Secondly, and this is a step a lot of people don't perform. You should bond the antenna ground system to the house ground rod system outside with #6 cable so they're at the same ground potential. If you don't bother to bond the antenna ground rod to the house ground system, it can create a loop when the antenna coax ground comes in contact with the house power ground at your HT system.........

brucek

[Goombaw]

Hello

i know this post is old but im trying to do kinda the same thing in a customers house i have a rack of electronics including a control 4 hc500, a sony da3300es and a sony cx777es( 400 disk changer) the customer also has an aditional surround sound system in another room where he wants surround sound from the 400 disk i have already ran a rg6 quad to the location one end is terminated with an fcon rca connector the other with an f connector in a wall plate then i connect to that and convert it to a rca with another pice of rg6 the total length is around 120 ft. I am not getting any signal. is there any kind of a booster or repeter that i can use?

any ideas??

thanks

[audioqueso]

That CD changer has a digital output, correct? Sure, they sell fiber repeaters.