Q. Can I use a video patchbay for S/PDIF signals?

By Hugh Robjohns

Is it possible to use a video patchbay, such as the one Studiospares sell, as an S/PDIF patchbay? The Studiospares one has 75Ω BNC connectors, so obviously appropriate 75Ω cables with BNC-to-phono connectors and/or adaptors would be required. From what I can see, the available S/PDIF patchbays, especially the programmable sort, are prohibitively expensive for the requirements I have.

Gavin

Mosses & Mitchell Musa.

Technical Editor Hugh Robjohns replies: Yes, it is perfectly possible to use passive video patchbays for routing S/PDIF (or unbalanced AES) digital audio signals — indeed, that is precisely what many professional installations actually do. As you say, the standard characteristic impedance for video systems is 75Ω, the same as that required for S/PDIF digital audio signals.

If you anticipate a lot of plugging and unplugging of patch cords, then its best to use a patchbay with video connectors designed for the job, such as the Mosses & Mitchell MUSA design. A BNC patchbay can be used just as reliably, but is rather more awkward to use. I'd stay clear of phono jackfields though, as these tend to become unreliable relatively quickly.

If possible, use BNC-to-phono cables (those designed for video applications will be ideal) rather than phono-phono cables with BNC adaptors, as the boundary between the adaptor and phono cable may well make the signal less reliable.

If you only need a few inputs and outputs, it may prove more cost-effective to use something like Canford Audio's modular patch panel system and install the required BNC sockets for the digital audio circuits, possibly along with other connectors to suit other applications (analogue audio, microphones, AES, MIDI and so on).

Published March 2005