FOH Cable Extention

[Bryan Cole]

Hello All,

I'm sure this has been visited before, but I need a longer FOH cable, abtou 16 feet. Near as I can tell, the cable contains CAN bus, VGA, Audio (headphones and Talkback) and USB.

I don't have a challenge getting a cable made, however does anyone know (Sheldon?) which signal is it that may need to be boosted? If CAN is the most length sensitive (I can't imagine USB, audio, or vga being the problem) can I gain a few feet (reduction in overall run length) by using interconnects between the sidecars that are just long enough (instead of the supplied ones that have a few feet extra each?

Please know I'm not planning to hold anyone at Digi accountable to this (I know this is an 'expiriment'), as I know the spec is 11 feet (I need 16). I'd just like some technical assistance knowing what kind of issues I might encounter, and maybe how the 11ft was arrived at. It is a fairly critical peice to this install.

Thanks so much to all!
Bryan

[Sheldon Radford]

Hi Brian,

Use of a cable other than the provided FOH Link is not supported by Digidesign.

In theory, the USB signals are the only ones needing an external booster at that distance; all other signals could be extended using a heavier gauge cable than what's currently used in the FOH Link cable. Pinout and connector details are provided for reference in the D-Show User Guide.

Sheldon

[M-ManLA]

I don't know if this will help but check out this site.

http://www.gefen.com/

they do make extenders that you might need.

[eytan]

Hi Brian,

Use of a cable other than the provided FOH Link is not supported by Digidesign.

In theory, the USB signals are the only ones needing an external booster at that distance; all other signals could be extended using a heavier gauge cable than what's currently used in the FOH Link cable. Pinout and connector details are provided for reference in the D-Show User Guide.

Sheldon

Hi Sheldon,

If only the USB signal needs boosting, can the booster be placed inside the FOH Rack or the Main surface? If there is a lot of demand for a longer cable, maybe Digidesign can offer a thicker/longer cable (as an option) and maybe a booster for user installation?

Does that make sense?

I find it that for permanent installations there is a need for the FOH Rack to be located further away in some situations.

[Sheldon Radford]

Hi Eytan,

This could be done but there simply isn't enough demand for it, and commercial "off the shelf " solutions are readily available. I realize it's a bit of custom engineering work to make a longer cable, but this can typically be absorbed into the cost of the installation.

Sheldon

[Duncan Stewart]

We've extended the length of our cable, though it wasn't plain sailing.
The biggest problem we had was with the CAN pairs.

This is eventually what we did:
4 CAN bus pairs through Canare AES - suggest using Gotham mini-AES instead... Canare is too stiff.
VGA: Fat, low loss cable - connected straight to monitor instead of going through the console.
USB: off the shelf USB extenders

All other connections were carried by heavier gauge cable, approximately quadruple what's found in the FOH Link.
Hope that helps - you should be able to do about 100ft.

[Sheldon Radford]

Thanks for sharing this Duncan. One important clarification: the maximum distance the CAN signals are qualified for is 75 feet. It may work beyond this under some circumstances, but it's really not recommended as random data errors can occur. The data errors will likely take the form of momentary control surface glitches, or possibly losing sections of the control surface altogether.

Sheldon

[[email protected]]

Hi Sheldon!

I'm about to make a longer FOH cable and I wonder if it's enough to run the CAN signals trough 90 ohm cable or do I need like the cables Duncan mentioned 110 ohm.

/Moses

[Sheldon Radford]

Hi,

Only 110 ohm cables suitable for digital signals should be used for CAN.

Sheldon

[Chris Johnson]

Just out of interest - i presume CAN bus is CAN bus? As in, the variations between manufacturers implementations are the data being sent, not the protocol spec in terms of the way data is transmitted?

Because, d&b D series amps use CAN bus for remote control of parameters, and i can get this to run hundreds of meters using STP Cat5 cable.

Maybe wiring the FOH cable with STP Cat5 for the CAN pairs will give you a greater length?

Electrically it makes sense - twisted pairs gives you a high CMRR and overall shield prevents excessive outside EM interference...