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Using interconnects for digital

gustav_errata said:
I knew that was generally the case, but based on what you say, it sounds like that is necessarily the case. Would you mind explaining why that is or otherwise pointing me to a resource that explains it? Is it something about the geometry that BNC avoids?
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The impedance is determined by the thickness of the conductor, the dielectric and the distance between them. Because of the design of the RCA it physically cannot achieve 75 Ohms impedance.

There can be issues with reflections with impedance mismatches where the signal travels down the cable hits the mismatch and a portion of it bounces back. Obviously this will happen at both ends and if the length of the cable is such that the reflections become "in sync" with the edge of a clock signal that will cause interference.

The magic number in digital cables is 1.5m but that can be any cable it doesn't have to be foo.

So there is absolutely no such thing as a truly 75 Ohm RCA terminated cable but as with many things in HiFi marketing takes these minor things to sell expensive bespoke cables.

PS all the above is a very simple explanation and I'm sure some ASR geek will be along to pick holes in my description or use of loose terms :rolleyes:
 
With a bnc the centre core connects directly to the reciever. With RCA the centre core is soldiered or crimped to another piece of metal. This corrupts the impedance. Some Canare plugs claim to be close to 75ohm as it is crimped close to the receiver end.

There are several other factors to consider, for example, what about the equippment, eg transport and dac. What connections do they use, how close to 75ohm are they, same for the receiver and transformer, if present. What about their quality. These are all usually unknowns.

Consequently there is no real way of knowing how any digital interconnect will perform.

It is probable that high quality professional broadcast cables will perform to specified standards.

Remember many manufacturers try to create an in-house sound style which may mean they intentionally deviate from transparent pass through, this can include equipment and cables.

Ultimately you need to try different cables see what you think. Personally I use 1.5m Belden 1694a these days because it is well made and reliable. Sound wise I have never noticed any significant difference with cables. I don't have golden ears.
 
Our esteemed Jim on here who literally researched and taught this stuff for a living uses TV/Satellite co-ax.
 
I tried different cables for digital, any old one will do just fine. Yes, even the freebie that came with your old VCR (yellow RCAs).
Forget about the whole thing. Those cable discussions are just surreal, but keep coming up. Will they end one day? 😇
 
PS once again none of this is HiFI specific, it is good old fashioned transmission theory and was calculated/standardised back in the 1960's long before "digital" was a thing in the audiophile world.

In the UK E1 (PCM30) telecommunications circuits use 75 Ohm coax for unbalanced or 120 Ohm for balanced.

Back in the 70's audio was being digitised at 8/8 and this is what your CD 16/44.1 or hires 24/96 or 24/192 is all based on. Nyquist theory and all the other lovely phrases you see bandied around in HiFi are from telecommunications.
 
martin clark said:
NO RCA plug, whatever is claimed, can achieve '75ohm' ; neither do any audio cable companies have any real understanding,
of the end-to-end reqts, to achieve ..such.

'They' really, do not.

..so if what you have, works, pleases-you: well - that's pretty much as good as it'll be; just enjoy.
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Hugely overlooked point - I’m running 50cm of proper AES/EBU 110 ohm cable between my DAC and upsampler…you reckon the XLR connectors meet the 110 ohm standard? I seriously doubt it 😆

As said, I’ll try swapping back to 1.5m of 75 ohm cable soon - don’t imagine I will hear a difference…but the 50cm items will go back in in a desperate attempt to tidy the cabling behind my rack 🥴
 
The thing to bear in mind here is it is a network cable, not an audio cable. The RCA connector is one aspect the audio community has got wrong pretty much from the off, it just doesn’t belong here, yet sadly most audio kit has them. It is far better served with an old-style BNC-terminated 10base2 ‘thin ethernet’ cable as that is really what this interface is. That’s exactly what I used to hook my Rega Apollo-R transport to my Chord DSX recently, though I had to hack off a BNC and stick an RCA plug on at the Rega end, which as Martin points out, is just the wrong plug for this interface. It can’t ever be the right one. It may “work”, but it is wrong no matter how expensive the cable!
 
How did we get here. Why did they ever start using RCA for digital?

And while I'm at it, toslink is rubbish too, the seockets seem to be designed to brake.
 
In my experience many analogue RCA cables aren't 75ohm for the cable itself, never mind the connectors, and there's no reason for them to be.
A "digital" RCA cable should be 75ohm coax but analogue cables are often shielded twisted pair construction which is more like 100ohms.
Whilst a non 75ohm analogue RCA cable may "work", a true 75 ohm one should be better for digital applications, all things being equal.
 
adamdea said:
They are basically the same (assuming use of coax. cable) and should work fine. if concerned the thing to use is actually analogue video cable (eg old fashioned coax tv cable) which is what is used in most good "digital" S/PDIF cable. It is cheap.
If you ask a magician, expect a magical answer.
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Yup. The reality is that for short cables I suspect pretty much any coax would do. I've certainly used low loss TV coax for long runs with no problems. In reality the chances are that almost no domestic digital out or in sockets are *actually* of the stated standard impedance across the band. Indeed, this is almost impossible to get when the range of signal frequencies in the pattern is wide and goes down so low. Real coax doesn't have an impedance which is the same from dc up.
 
martin clark said:
NO RCA plug, whatever is claimed, can achieve '75ohm' ; neither do any audio cable companies have any real understanding,
of the end-to-end reqts, to achieve ..such.

'They' really, do not.

..so if what you have, works, pleases-you: well - that's pretty much as good as it'll be; just enjoy.
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Canare is the only maker of BNC->RCA adapters that are true 75r. And they have been discontinued IIRC. On a Laird 75r SDI BNC cable, the Canare RCAP adapters do indeed test out at 75r.

As far as an RCA connector being true 75r, I'm not aware of one, though if it does exist, Canare would likely be the one to have made it.
 
I've tried phono, BNC, adapters etc and have not found any correlation between the cables being technically correct and sounding better. I had two cables which were the same except one was long and the other short. According to the reflection theory they should've sounded different but they sounded the same.

Any differences I could hear were quite small which leads me to believe that it's a very tolerant system. I guess it'll depend on how your particular hardware works too.
 
One of the key purposes of digital signalling and information representation/handling is to make it 'robust' against most of the mechanisms that limit analogue signalling. That's why engineers like it.
 
While my NAS is monopolized by me doing a total copy of the music (approx 5To) to a new set of exteranl hard drives, I've reconnected the Cambridge CXU to the DAC using one length of Kondo Vc analogue interconnect (the VzII digital is too short since I moved things around).

Works fine. In fact, I'm rather enjoying Anticipation by Carly Simon.

This is the reverse of what I used to do with Kondo VzII digital interconnects for analogue between pre and power amps.
 
My dCS Delius has both XLR balanced & RCA single-ended outputs. I’ve been using the RCA happily for a month or so via my new to me Purcell upsampler. I recently tried XLR out and was disappointed compared to RCA out, which sounded much better.

Both cables around 3m long, both studio microphone cable - RCA using Cordial & XLR using Neutrik- why such a large and noticeable sound quality difference? Connectors are old Quad on RCA & Neutrik on XLR - on XLR I have joined the screen and negative together at RCA end, should I try separating them?

Thanks, Richard
 
Dowser said:
My dCS Delius has both XLR balanced & RCA single-ended outputs. I’ve been using the RCA happily for a month or so via my new to me Purcell upsampler. I recently tried XLR out and was disappointed compared to RCA out, which sounded much better.

Both cables around 3m long, both studio microphone cable - RCA using Cordial & XLR using Neutrik- why such a large and noticeable sound quality difference? Connectors are old Quad on RCA & Neutrik on XLR - on XLR I have joined the screen and negative together at RCA end, should I try separating them?

Thanks, Richard
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No idea...
With my fully balanced pre and power amps, balanced via XLR is THE way to go for both phono stage and DAC.
 
For what it's worth, Jeff Day over at Jeff's Place was extremely impressed by, from memory, using a Belden 8402 for digital. and he has some serious Japanese style high-end kit. I might be wrong but seem to recall the tip came from one of the gurus behind SPEC amplifiers. If i'm talking rubbish then shoot me down, but there is definitely an interesting article on this on Jeff's site for those wishing to dive deeper into this
 
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