Dedicated digital COAX cable vs. stereo RCA

[mkrzych]

Hello,

I have one question. Is it something special in the digital COAX cable that I cannot use just one stereo cinch RCA cable? Both are shielded and both seems to work fine. Any impedance issues or something?

[Kal Rubinson]

Hello,

I have one question. Is it something special in the digital COAX cable that I cannot use just one stereo cinch RCA cable? Both are shielded and both seems to work fine. Any impedance issues or something?

In theory, digital coax is a 75ohm connector specified for digital interfaces while standard RCA cables are of undefined impedance. In practice, plain RCAs will work for short digital connections and, of course, digital cables will work for analog. Also, it is doubtful that, on the digital cables, the RCA connectors, themselves, are truly 75ohms and that BNCs are the proper way to go.

 

Messy but that's the way it is.

[mkrzych]

Thanks Kai. So for 0.5m of connection should I rather avoid using RCA in general or if it's working it's just fine? Just not to generate the additional cost.

[4est]

Is it working just fine? I'd at least try a cheap video cable or two if you do not want to spend anything/much.

Thanks Kai. So for 0.5m of connection should I rather avoid using RCA in general or if it's working it's just fine? Just not to generate the additional cost.

[mkrzych]

Just wondering if changing that cable for better dedicated coax may have positive impact on the sound? Taking into consideration the Ohms in digital domain.

[Speedskater]

For coaxial digital interconnects shorter than about 10 meters (33 feet) just about any reasonable RCA coaxial interconnect will do (excluding junk throw-away cables). Over that length you will need a 75 Ohm cable.

At the low RF frequencies of digital audio, the connector (RCA, BNC) is such a small fraction of a wave-length, it has no impact on the signal quality.

[sandyk]

Speedkater

Sorry, but many members will not agree with that claim. To my surprise I heard an improvement with a cheap Digitor 75 ohm digital lead from Jaycar (Au.) over that of a beautiful thick white coax patch cord (RG213 ?) salvaged from a Telstra 12MHZ carrier system, after one of it's plugs broke. The leads were the same length (1.5M) and the patch cord one used high quality RCA plugs.

 

Alex

[crisnee]

I would just see if I could borrow a better quality cable and try it. Then you could see (hear) for yourself.

 

I don't usually concern myself much with cables, but I did have an experience where I noticed a difference when using a cheap run of the mill 10 ft. 75 ohm cable vs. a better quality 5 ft. 75 ohm coax cable. The former sounded harsh compared to the latter.

 

Chris

[Brad O'Toole]

Kal has it right...almost. Many digital audio 75 ohm cables use a standard audio RCA connector. A proper 75 ohm connector must have a 360 degree contact for the shield or it will cause an impedance change, which will alter the signal. These connectors do exist. Video cables are built the same way so you are not getting ahead by getting a cheap video cable. The advice to try a cable is a great one. The proof is always in the experience when it comes to audio. For full disclosure I work at Transparent Cable and of course our cables all have the proper connectors. They start at $100 (100 euro in Poland) so I realize the idea of an inexpensive cable with the proper connector may be out of reach with our products, if not give it a try.

[GoldenEar]

I recently connected my LINN Akurate DS to my Devialet using a dedicated digital cable from Inakustik (100 EUR) that worked well in a previous setup. I was not able to play 192 kHz files with this cable. So I picked up an old RCA cable (200 EUR for the pair at the time) and it worked without a flaw. Thus RCA can be even better than a "digital" cable.

 

Regards

Kay

[sandyk]

I recently connected my LINN Akurate DS to my Devialet using a dedicated digital cable from Inakustik (100 EUR) that worked well in a previous setup. I was not able to play 192 kHz files with this cable. So I picked up an old RCA cable (200 EUR for the pair at the time) and it worked without a flaw. Thus RCA can be even better than a "digital" cable.

 

Regards

Kay

 

In that case you have a problem with either the Inakustik cable due to a fault that has developed ,(crimped connectors for example) poor design, or a marginal problem that is SPDIF level related in your equipment. Some high priced Audiophile cables don't appear to meet the correct specifications.("Snake oil"?)

There was a good example of that posted in C.A. recently about an expensive USB cable that used 2 lots of twisted pairs without appropriate screening. Some systems are more forgiving than others of poorly designed interconnects. Incidentally, many interconnects are of a coaxial type construction with an impedance often around 65 ohms, so it isn't surprising that some may work reasonably well for digital audio.

 

Alex

[mkrzych]

Thanks a lot guys for the explanations. I will stick with that RCA - it's 0.5m Chord Crimson VEE3 wire. So far worked fine.

[Kal Rubinson]

Kal has it right...almost. Many digital audio 75 ohm cables use a standard audio RCA connector. A proper 75 ohm connector must have a 360 degree contact for the shield or it will cause an impedance change' date=' which will alter the signal. These connectors do exist.[/quote']Perhaps they do but one cannot assume that merely appearing to have a full contact shield is sufficient. Nor, of course, is relying on a cable manufacturer's blurb. Can you name a few that qualify?

[Mike48]

Hi Kal!

 

Canare offers a series of RCA plugs that they state are 75-ohm. I know that Blue Jeans Cable uses them; I don't know who else does.

 

Canare Corp.: RCA Crimp Plugs: 75 ohm RCA Crimp Plug(RCAP-C Series)

 

On their site, Blue Jeans says that they consider them the best of the RCA plugs at matching a 75-ohm impedance, but not as good as BNC connectors.

 

Some consumer manufacturers use BNC for SPDIF. I wish more did.

 

Mike

[Kal Rubinson]

Hi Kal!

 

Canare offers a series of RCA plugs that they state are 75-ohm. I know that Blue Jeans Cable uses them; I don't know who else does.

 

Canare Corp.: RCA Crimp Plugs: 75 ohm RCA Crimp Plug(RCAP-C Series)

 

On their site, Blue Jeans says that they consider them the best of the RCA plugs at matching a 75-ohm impedance, but not as good as BNC connectors.

 

Some consumer manufacturers use BNC for SPDIF. I wish more did.

 

Mike

I know about those and I am skeptical. Would like to see some proof.

I, too, would prefer BNC to be standard.

[PopPop]

I would just see if I could borrow a better quality cable and try it. Then you could see (hear) for yourself.

 

I don't usually concern myself much with cables, but I did have an experience where I noticed a difference when using a cheap run of the mill 10 ft. 75 ohm cable vs. a better quality 5 ft. 75 ohm coax cable. The former sounded harsh compared to the latter.

 

Chris

 

Exactly right Chris! Last year the digital cable that runs from my CD player to my DAC quit (broken solder joint). I borrowed a few samples from the audio store and found a 2.5X upgrade that gave me a nice improvement in the sound - more resolution and depth. Then I was left to deciding to fix the old or spend the extra money for the new. It seemed like an easy decision.

[wwaldmanfan]

Hi Kal!

 

Canare offers a series of RCA plugs that they state are 75-ohm. I know that Blue Jeans Cable uses them; I don't know who else does.

 

Canare Corp.: RCA Crimp Plugs: 75 ohm RCA Crimp Plug(RCAP-C Series)

 

On their site, Blue Jeans says that they consider them the best of the RCA plugs at matching a 75-ohm impedance, but not as good as BNC connectors.

 

Some consumer manufacturers use BNC for SPDIF. I wish more did.

 

Mike

 

I upgraded from a Canare 75Ω cable (~$35) to a Black Cat Silverstar 75 ($150) to connect my MF V-LINK192 to my Peachtree DAC•iT, and heard an immediate improvement in SQ. The Black Cat uses BNC connectors, but includes proprietary BNC/RCA adaptors, which I am using, and they seem to work well.

 

Silverstar 75! – Black Cat

[bdiament]

Hi 4est,

 

Is it working just fine? I'd at least try a cheap video cable or two if you do not want to spend anything/much.

 

Agreed. There is *supposed to be* a difference between a cable meant for digital audio or video vs. a plain analog interconnect.

The fact that some manufacturers may not use the right connectors or cables does not mean using a proper design will have no sonic impact.

 

In my experience, there is a quite noticeable sonic difference between using a fine analog interconnect and using a fine digital interconnect. Cable length can be important too.

I suggest folks listen and compare for themselves rather than taking someone's word (including mine) for what they will be listening to.

 

Best regards,

Barry

Soundkeeper Recordings

The Soundkeeper | Audio, Music, Recording, Playback

Barry Diament Audio

[MykhailoM]

There are different designs used for both type of cables either for analogue or digital signal. These signals are different having different audio format. If you would use a similar type of cable for either signal source you would get a very audible difference. I have tried either way and every time I can hear a distinctive difference. I highly recommend to use a dedicated cable for a specific audio course. I personally use Malbru Silver CX coaxial cable and couldn't be happier, an absolute winner in my tests. Auditioning several pares is a good way to chose what you need.

[JohnSwenson]

Hi Kal!

 

Canare offers a series of RCA plugs that they state are 75-ohm. I know that Blue Jeans Cable uses them; I don't know who else does.

 

Canare Corp.: RCA Crimp Plugs: 75 ohm RCA Crimp Plug(RCAP-C Series)

 

On their site, Blue Jeans says that they consider them the best of the RCA plugs at matching a 75-ohm impedance, but not as good as BNC connectors.

 

Some consumer manufacturers use BNC for SPDIF. I wish more did.

 

Mike

 

The Canare plugs make a proper 75ohm connection to the 75 ohm coax (as opposed to how most audio RCA plugs connect to the cable), BUT the RCA connection itself is NOT 75 ohm.

 

To my knowledge WBT is the only company that makes true 75 ohm RCA components. Their Nextgen series has RCA jacks that have sort of a spiral looking metalization over an insulator, when you use this with a connector such as the above Canare it is 75 ohms. But this means making the gear with this connector.

 

They also make special RCA plugs that are not a complete barrel type outer contact, I'm not sure if these will give true 75 ohm connection if used with a standard full surround RCA jack. Or only if used with their own jacks.

 

John S.

[One and a half]

When using a dedicated coax cable (with RCA) Oyaide Continental (0.7m) , the situation when switching on a nearby fluorescent lamp would transmit through the speakers, loud crack quite nasty.

Determined that the cable was the problem cause it was the last one installed, hehe, replaced with 75 Ohm TV coax Quad RG6 with F to RCA adapters. No noise breakthrough now at all. I use the same cable for antenna infeeds as well as digital coax from now on.

 

The RG6 is better crimped, although screw on connectors can be used, not as good though for long term reliability. The toolkit is less than $60 which includes the cable stripper, crimper and tool to loosen the connector.

 

So purpose made digital cables can cause more problems than they are meant to solve. RCAs should be used only for phono connections from moving coil/magnet signals as per the original intention. That the RCA has come so far shows a testament to being cheap has a high priority for manufacturing.

[Oystein]

For a lot op people it is very confusing to talk about 75 ohm connectors as when measured a connector or even an assembled 75 ohm cable they never measure 75 ohm ... even I tried the first time I was confronted with dealing with such hardware.

 

Please correct me if I am wrong .. I use this post now to fill in the blanks or correct the errors in my thinking so I hope to learn from this too and hopefully some other people can benefit from this too ;-)

 

As far as I understand the 75 ohm (or "older ?" 50 ohm) systems are based on the fact that there is a 75 ohm resistance at the receiving end.

This is why it is called 75 ohm cable, plug etc.

 

This 75 ohm resistance together with cable properties like inductance, capacitance creates an L-C-R network which will work fine as all these properties are designed to work fine together for the max. bandwith and cable length as what a 75 ohm system has in their design specifications.

 

The reason for using BNC instead of regular RCA is that the sleeve / bushing which is crimped in a hexagon arond the cable will create to optimum connection to the shielding where the regular pigtails found in assembled RCA connector with hurt performance as supbar shielding and lower bandwith etc.

 

So the same cable can perform differently with RCA or BNC and non 75-ohm cable with BNC can still limit bandwith and destroy the shape of the digital square pulses by having capacitances and induction other than ideal for 75 ohm.

 

I am correct so far ??

[Speedskater]

The 75 Ohm or 50 Ohm impedance under discussion here is;

'Radio Frequency Characteristic Impedance'

This doesn't stabilize until the frequency approaches 1 Megahertz.

And it doesn't matter until the cable or component approaches about 1/4 wavelength of the frequency in question.

So for SP/DIF a 1/4 wavelength is about 25 feet. Neither RCA nor BNC connectors don't have an impedance at SP/DIF frequencies.

[sandyk]

The attached chart may be of interest to some.

 

[JohnSwenson]

The 75 Ohm or 50 Ohm impedance under discussion here is;

'Radio Frequency Characteristic Impedance'

This doesn't stabilize until the frequency approaches 1 Megahertz.

And it doesn't matter until the cable or component approaches about 1/4 wavelength of the frequency in question.

So for SP/DIF a 1/4 wavelength is about 25 feet. Neither RCA nor BNC connectors don't have an impedance at SP/DIF frequencies.

It's a little more complicated. The simple formula above is only for pure sine waves. An S/PDIF signal is not a pure sine wave, it is a digital signal which contains sharp ramp times, these "edges" contain harmonics which go up much higher than than the fundamental. These harmonics ARE high enough in frequency to be affected by transmission line characteristics of digital interconnects.

 

These transmission line effects can cause significant changes in the shape of the edges of an S/PDIF signal. These edge differences can cause significant behavior in the PLLs which are used to extract the clock in many S/PDIF receivers.

 

It's not just simple edge rate changes, impedance mismatches WILL cause reflections, even for S/PDIF signals. If you feed an S/PDIF signal into a TDR (time domain reflectometer) you CAN see reflections from a real S/PDIF signal. The amplitude of those reflections depend on the impedance mismatch and the ramp time of the signal. Slower ramp times cause less intense reflections. BUT slower ramp times can cause many PLLS to generate more jitter. It's a complex tradeoff made by the designer.

 

The length of the interconnect has several different effects on this system. Short interconnects cause the transmission line effects to occur at higher frequency which generally results in better quality edges and less intense reflections, BUT it can cause the reflections to be far more disruptive to a receiver.

 

Even though there is a standard for impedance, very few transmitters and receivers actually meet this, complicating things significantly. A cable which causes a good match with one component may be very wrong with another.

 

The over all result is that the situation is far too complex to make generalizations. The adage "try it yourself and see" is REALLY appropriate here. One cable can be great with one set of components, not great with another, and another set of components may be quite insensitive to the difference between two specific cables.

 

The impedance mismatch caused by RCA jacks over say BNC jacks (as long as they are real 75 ohm BNCs) DOES make a difference in the signal. Exactly what the difference is can vary depending on the cable and the equipment on both ends. How the receiver responds to these differences also varies.

 

So going from RCA to BNC MAY make a difference in a particular situation and it may also not make a difference. Its very system dependent.

 

John S.