Length of digital cable?

Arnett - 18 feet is totally unnecessary and you can do a LOT better than Belden 1694A. Many years ago when I still had a set of inexpensive cable from 1964A. I have a giant spool of it. I finally concluded that it cannot be done.

If you want a fantastic sounding cable, get the 4 foot BNC-BNC cable with RCA adapters from my website for $250. It is literally unbeaten. Use the pull-down on this page:
http://www.empiricalaudio.com/products/off-ramp-converter

Here are some reviews:
http://www.audiocircle.com/index.php?topic=115008.msg1208227#msg1208227

http://www.audiocircle.com/index.php?topic=115008.msg1208373#msg1208373

The optimum length of a digital cable is entirely a function of the risetime of the signal on that cable due to the driver in the source device. The analysis is in my white-paper here:

http://www.positive-feedback.com/Issue14/spdif.htm

Steve N.
Empirical Audio

The BNC-BNC cable is on the pulldown menu at the top of the Off-Ramp page. It is generally sold as an accessory to the Off-Ramp, but can be purchased alone. You can also email me and I can send you a paypal invoice.

Steve N.
Empirical Audio

HK990 issue was likely a ground-loop issue.

One must take care to use the optimum AC outlets and circuits for digital, particularly when the devices don't have galvanic isolation from each other. Never use two different phases from a panel and best to use the same circuit for all devices.

Steve N.
Empirical Audio

"I was using separate circuits for digital and analogue. That is, transport was on separate circuit but was using the amp's onboard D/A converter."

That could easily do it.

Camb - Its true that RCA connectors are more like 45 ohms, but if you use good 75 ohm BNC adapters like I do, the effect is negligible. If you have BNC on either the output or input device, you can use the native BNC which is better.

The benefit is really the cable itself and how it is terminated to the BNC and shielded. It cannot be just any 75 ohm BNC. The BNC must be designed specifically for that particular cable to avoid an impedance change at the cable termination.

If you terminate to an RCA, it is very difficult to avoid a big impedance discontinuity because it is never a good match for the cable.

Steve N.
Empirical Audio

"Although BNC would theoretically be preferable to RCA connection, there is actually next to no audible difference between an spdif using either. Steve mentions that the BNC must be designed for a particular cable, which frankly is a dubious statement. The connectors 'are what they are', and the cable that exists to connect them together should offer as close to the 75ohm Zo as is possible, which is not difficult."

Whether you hear differences will depend on your source and your system. If the source is truly low-jitter and has fast risetimes to insure that the low-jitter is maintained through the receiver, the BNC will make a BIG difference.

Termination of the coax to the RIGHT BNC connector is critical. Even a millimeter difference in diameter inside the connector will change the impedance. Many so-called 75 ohm connectors are also not 75 ohms exactly.

"If using RCA connectors, the shorter the better, i.e. Furutech FP126, and designing the cable to terminate at 75ohms exactly can make a perfect match. Using adaptors also makes little difference, both on a scope and audibly. Saying that, I do agree that more equipment manufacturers could do with offering them.
Cable length should not be an issue if the said cable is an exact impedance match for the output and input, as refections should not occur."

Also untrue. There will ALWAYS be reflections, even in the best of cables and connectors. The reason to have a 1.5m minimum length as recommended in my paper is to insure that when those reflections get back to the receiver, that it is not when the receiver is detecting the edge. Its just common-sense.

You obviously did not read my white-paper, which has been the standard for S/DIF cable length for many years now.

Steve N.
Empirical Audio

The 1.5m cable length is a good guideline. Shorter cables can be problematic depending on the signal risetime. The 1.5m length insures that any jitter causing reflections occur too late to have any impact. Really short, say 6 inches can also be good, but between 1 foot and 1.5m, you are taking a risk IMO. Dont spare the change.

Adapters do make a difference, but again depending on the signal risetime. The faster the risetime, the better the jitter result. Here are some plots showing jitter with different cables and adapters:

http://www.audioasylum.com/forums/pcaudio/messages/13/132743.html

I have been doing this a LONG time and I know what I'm talking about.

Steve N.
Empirical Audio

The best performing and also the best price coax cable is my 4-foot BNC-BNC cable with RCA adapters. Beats everything in customer shootouts, at any price. Silver with expanded Teflon dielectric and terminated to low-loss true 75 ohm BNC connectors. A steal at $250

Steve N.
Empirical Audio