Digital XLR vs Digital RCA

@auxinput - re: your statement

I have done many tests on different RCA connectors, using RCA that are designed specifically for digital (i.e. DH Labs RCA-75) as well as several extremely expensive and high end analog RCA (such as WBT, Furutech, etc.). In all cases, a good low-cost BNC connector was superior to all RCA connectors.

I agree with your statement regarding the RCA’s you have mentioned - they are definitely NOT suited to the task and one really should use the impedance matched RCA’s specifically designed for digital use

A QUESTION: Have you had the opportunity to try the KLE Innovations Harmony line of RCA’s?

They are perhaps the only RCA that is capable of being used for either digital or analogue use.

I (and many others) have used these RCA’s with great success in constructing cables for use as digital interconnects.

I tried them a few years ago, even before KLE Innovations brought out their line of digital interconnects and could not believe how much better they performed than my impedance matched RCA’s that came on a digital cable from Van den Hul

Selecting a suitable geometry, wire quality and the insulation, becomes more applicable to improving cable performance once the Harmony RCA’s are used

Regards - Steve

@williewonka - yes, I think I have used the KLE.  Well, it was the previous Eichmann Silver Bullet plugs (which are the same thing).   As with all cables, it is system dependent.  The sound was okay, but just a bit too bright for my taste and system.  I don't know that it really improved the sound for me. 

@auxinput re:...

Well, it was the previous Eichmann Silver Bullet plugs (which are the same thing).

Actually - when you get down to the nitty-gritty, these are two "similar looking" RCA designs, that do have quite different levels of performance.

Granted
- both are originally developed but the same guy - Keith Louie Eichman.
- so there are similarities in "design concepts", i.e. the tiny neutral pin in the collar
- but the subtleties are in the pin design, metallurgy and casement materials
- the Harmony RCA’s are a more refined version of the Silver Bullet.
- and so the sound is more refined and more complete

I too started with the Eichman Silver bullet on my turntable - I then tried the Copper Harmony followed by the Silver harmony.... and finally the Absolute Harmony.

I found the Copper Harmony to have a more complete and more detailed sound compared to the original Silver Bullet on analogue cables and the Absolute Harmony to be the very best in the Harmony line.

Anyhow - the topic here is all about Digital performance
- So as an experiment I decided to replace my purpose built Van Den Hul SPDIF cable with one of my analogue interconnects with the Absolute Harmony RCA’s
- to my surprise it sound better - a lot better !
- less glare, more details, improved clarity, better imaging
- how could this be? the cable was not even designed for digital use

I contacted KLEI and asked them about this - They confirmed that the Harmony RCA’s are in fact a very good choice for SPDIF interconnects and that they do not suffer from the same issues that other brands of RCA’s experience, because of their design and materials used.

Shortly after our email exchange, KLEI released their SPDIF cables, which I was asked to review :-)
http://image99.net/blog/files/category-klei-gzero2d-spdif.html

Their are several postings about the Harmony RCA’s in this thread - from both analogue and digital perspectives
https://forum.audiogon.com/discussions/duelund-conversion-to-diy-helix-geometry-cabling

I cannot offer any explanation as to why these RCA’s work on SPDIF cables, but they do - and very successfully.

Combining them with the right geometry results in a cable offering exceptional performance - in either the analogue or digital realms.

Regards - Steve

Digital interface of SPDIF signal is of a low Fr. nature. It may go up to 48KS/Sec, or more like 44.1KS/Sec with home equipment.
As so, cable impedance, ending connectors etc' are of less significance.
When cable do make a difference, is mostly due to a poor PLL at the receiving end. 
If the cable would be a disaster, there would be dropouts. SPDIF has no Acknowledgment of data received or massive correction methods. 
The claim it has no dropouts, but sounds less good, shows of a digital phenomena inflected over the sound...It is called jitter.
Jitter should be taken care by a circuit called PLL. All data receiving devices must have one. If the PLL is good, the cable should make no difference. If the PLL is not good enough, you are dependant on the cable. That doesn't ensure you are good. It only proves that one cable sounds better. No one claims it is now perfect!
When all digital cables sound identical, the PLL is good and it won't get better due to "digital cables".
All data transfer methods, would try to eliminate data error at transmission. So is SPDIF. The fact, that the cable gets so much attention is wrong. The inventors never meant to allow digital cable makers, make a fortune, from their poor design. The fact that we are there, and this and other threads deal with the subject, is so wrong.