Recommended RCA Coax Digital Interconnect?

Go for a longer digital coax.

To avoid confusing reflections at the receiver the suggestion is to use 1.5 metres coax, at least.

With a 1m length cable the reflection of a digital transition is likely to arrive at the receiver chip about the same time it is sensing the subsequent transition.

 

Length is an interesting one.
I have about 0.5m currently, also a 1m - can't any difference but I can easily build a 1.5m - that's tonights DIY sorted...

 

Steve, in theory 0.5m coax may also cause jitter. In a 0.5m cable the reflection caused by differential impedance will still superimpose before the receiver chip samples the original transition. Above 1.5m cable the reflection voltage will superimpose on the original transition voltage after the time the receiver chip has sampled the transition.

Whether the jitter is audible is another question, if you are able to detect jitter caused by the impedance of RCA plugs then the longer coax is worth trying on your ears.

For my money, even if all impedance-induced jitter is more theoretical than audible, the tiny cost of a longer cable will allow me to sleep better at night.

Good luck with the cable length test. Did you also test the jitter benefits of 75-ish ohm RCAs versus regular RCAs?

Tony

 

Excellent.

I happen to have a drum of twin HT100 cable - well what's left of it after making loads of speaker (Ubyte) and other cables for myself and pals.

So made up a new 1.5m long cable. After about an hour (amp warmed and cable a little 'burnt' in)...

I interpret the sound as different.
How?
Well, difficult or critical vocals that before wanted to make me change tracks are better resolved. Some of Sheryl Crow's stuff came in to this category. I put this down to poor recording or mastering before.
I think I would be kidding myself to say that other frequency bands are improved - it is easy to imagine perhaps -or wish it to be so. Certainly not worse.
Some of the echo and timbre on Dire straits Every Street certainly sounded great. Goldfrapp also pulsed well.

It's a fairly subtle change but quite sweet - Thanks for the tip Tony.

I still think hundreds of pounds for a digi coax is fairy dust - until I hear one and am converted to the great norse god Valhalla

BTW what makes an RCA 75ohm imp? Is it the fact that the core to screening relationship is maintained as well as possible so that the plugs are an extension of the cables?

I think I can see the importance if the cable was say a 50m cable with RCA male to an RCA female with another 50m of cable carrying the signal.
BUT we are terminating to RCA sockets on equipment and on the other side they are just open with soldered on core and screen - so can a plug make that much difference in this use mode? I guess you could carry the 75ohm bit further in but eventually it gets to point to point wiring as in my tube amp or a circuit board... Is it worth it?

 

Just spotted this thread...

It so happens that I have a Virtual Dynamics Master RCA digital I/C that I would part with. But you may already be committed elsewhere?

 

75 ohm is the standardised impedance - it should be from the traces on the Transport chip right through all the wiring and connectors to the traces on the Receiver chip in the DAC. Each time impedance changes it causes a 'shock' which can propogate back to the driver, until it hits another impedance change and reflects forward again etc etc. These reflections superimpose their voltage on the transition voltage thus degrading the quality of the transition.

Yes you can find impedance mismatches everywhere, still it is desireable to minimise where possible. When connecting a 75 ohm impedance digital coax cable into a RCA socket on the CDP or DAC which is not 75 ohm you have an unavoidable impedance mismatch, whether or not the interconnecting RCA plug is rated 75 ohm impedance or not. Equally fitting an RCA 75 ohm socket on the CDP/DAC won't avoid an impedance mismatch unless the wiring behind it is impedance controlled and the circuit boards are 75 ohms too. The idea behind longer coax cable is to minimise the impact of the potential impedance mismatch created in the cable by delaying the reflection until after the transition has already been sampled.

What makes a 75 ohm RCA plug? I believe the physical dimensions of the RCA plug render true 75 ohm impedance impossible, but I'm not an electronics engineer. Most RCAs do have a soldering point for the inner core and for the braid (very non-coax!) a long way from the connection tip - as you say Steve, the best designs are RCA plugs which fit the cable layout right up to the tip.

There is no need to worry about matching impedance beyond the DAC so don't rewire your amp! Impedance is an issue only for the digital signal because of its frequency and shape. After the DAC you have an analogue sine wave and impedance is not an issue.

Tony

 

Thanks - more things to try, which is always fun.

Have you heard of

http://www.bluejeanscable.com/articles/75ohmrca.htm

They say to have true 75 ohm RCA's...

 

They are using Canare RCAP connectors which are as close as anything else to 75 ohm impedance. Also Canare connectors come in different sizes to match different cables widths.

My current coax was donated to me but it is amateur-constructed with screw-up death-grip RCAs and frankly it has proved troublesome and anyway is too short. I recently ordered a pre-terminated cable from the US - with Canare connectors - and am waiting for this $32 toy to arrive. I see Bluejeans recommend Belden cable although what I ordered is fitted with Canare cable LV-61s, but I'm sure it'll still be good.

When it's all here there's gonna be a listening session with my small band of believers, non-believers and generally not-interesteds: comparing the 6 foot Canare against the 0.5m RCA coax, borrowed expensive Missing Link coax, and QED plastic/TOS optical...

Tony

 

FWIW,I have some Canare 75 ohm rca'd belden digi cables and found them to be quite forward/ brash at the top end but good bass(1m long)

 

Tony,
I look forward to 'hearing' the result of that test.

 

I'm looking forward to the comparison too - tho' having checked out MISSING LINK i'm giving them a miss and my 'quality' benchmark will be from ECOSSE CABLES who use copper RCAs.

Will be choosing between several grades of cable and connectors to keep budget sensible. Ecosse Cables's top grade coax is shielded which is bit of a luxury as far as coax is concerned so may put money into their better plugs instead.

Anyone have experience of these tasty-sounding products?
http://www.ecossecables.co.uk/Tables/table_frameset7.html

 

Cable length in an interesting perspective, and one that I can technically understand would have a bearing on sound.

I have had a couple of days with The Missing Link Binary Star (0.8m) and have been listening to it versus the Chord Prodac (0.5m).

My initial impressions was that he ML has a more depth and bass, but that the Chord has more top end (treble) detail on certain tracks (Keane / Atlantic for example). I need to listen to some more stuff. Overall, the ML is more my type of sound .... perhaps a longer cable will give a bit more of the detail that's in the Chord? I think I'll get on the phone to Jan on Monday morning.

 

So after an extended listening session, with a bottle of Fleurie, to my taste the Missing Link Binary Star Cryo'd lead wins it over the cheaper Chord Prodac.

Tracks played:
Kate Bush - Man With The Child in His Eyes
Goldfrapp - Black Cherry
Air (with Beth Hirsch) - You Make it Easy
The Beloved - Sun Rising
David Sylvian - Orpheus
The Sundays - Monochrome

overall the Chord's are "brighter" than the ML's. For example the trumpet solo on Orpheus was almost tinney in comparison to the robustness of the ML. The ML has more depth, and a much more stable bass. It lacks nothing in detail to the Chord (as heard in Beth Hirsch's vocals, and even more so in Harriet Wheeler's on Monochrome).

I will call Jan on Monday and order the 1.5 metre length as per the earlier suggestions.

 

i agree with what you have said RIPit, ive compared the ML cable to the chord signature at length, and found the signature bright, brash and metallic sounding. I never enjoyed it.

The ML is a smoother and at first seems softer, but extended listening reveals that all the detail, air, space and timbre are in there, they just arent shoved in your face the way the chord cable does.

 

Rip,
If you haven't tried the bog standard ML I 'd recommend you give it a go-full refund if not satisfied anyway so all you've to gain is about £60/90.so you could order both and just keep the one you like best.
The cryo does initially sound really lush but after a while it's deep soundstage and ambience began to sound very artificial to my ears-to the point I thought I had a phasing fault on my xta digital xover, even started stripping my system down trying to isolate what was up then had a DOH! moment and I dropped the bog standard ML back in and solid focus returned.

 

Cooky thanks for the recommendation. You are spot on as the basic ML is really cheap. I will ask Jan to send me a 1.5m length of both. My impressions will be posted.

 

Oh my good God! I am a firm believer in good cables but please don't spend 500 quid!!

In all seriousness, I implore you, please buy an NVA digital soundpipe from eBay. They are only 35 quid and you won't find a better cable for 500.

 

Yep, I agree, NVA just shades the ML IMHO tho' it is very close.

 

Thanks stugeek ... I have just mailed them to get a price for a 1.5m length. Will probably be around £70 which will be slightly more than the basic ML, but a lot less than the ML Binary Star.

 

You're more than welcome RIPit.

As a by the way, if you are already placing an order with them, do try one of their analogue "soundcords" - currently 10 quid for 70cm (usual price £35). The soundcords are "better" than the £100 Chord and VdH alternatives when used in my system. My father has also had similar experiences with them - he was all but ready to replace his aging Shure/SME/Technics system when I gave him a spare soundcord and now he's decided not to bother!