BNC vs. RCA for Digital - BNC Rules.

[Lizard_king]

For those of you who use separates for digital, like a transport and DAC, the SPDIF coaxial normally has a RCA jack. Use a 75 ohm BNC jack, it is a true 75 ohm connection to bring out the music. I am using a BNC cable that is made for digital (stereovox/stereolab XV ultra) with the M2tech Hiface for my computer with a BNC. I had the rCa jack o n my DAC pulled a Kings 75 ohm jack is there and the SQ is much better. The analog sound not is so good!

Liz

[tmazz]

It is all about the connector impedance. RCA plugs are very difficult to make at 75 ohms, a 75 ohm BNC is a snap. Nagys cable make a digital cable with a proprietary RCA connector that is almost exactly 75 ohms. (While this helps with the male end I would think you are still at the mercy of your hardware manufacturer as to the impedance of the females jacks  on your equipment which is why BNC is still a more reliable solution) This may account for some of the very positive reviews it has gotten, in spite of it's sub $100 retail price. Rollo had a demo piece recently and absolutely loved it.

Here is a technical explanation from the Nagys web site:

RCA Impedance

    This is a phenomena that happens only at higher frequencies.

    In consumer products the load is 75 ohm and in military it's 50 ohm.
    So, when you have a cable that goes from your transport to DAC,
    everything must be 75 ohm, this includes the female RCA connectors,
    male RCA connectors and the coax cable itself.

    If one of these components is not true 75 ohm part of the signal will
    reflect, but only at high frequencies, like the ones digital signals are
    transmitted in.

    If the cable it 75 ohm and the connector is 70 ohm only a small
    fraction will reflect, however if the cable is 75 ohm and the RCA is
    40 ohm (which is typical for most expensive/fancy so called audiophile
    RCA connectors out there) significant part of the signal will reflect.

    First, this reflection makes the signal weaker and second, the 
    reflection can cause an avalanche effect where it disturbs the signals 
    behind it.

    This is all very bad for an instrumentation type cable.

    Most RCA connectors are 40 ohm. At high frequencies, the
    shape of the connector and the thickness of dielectric will determine
    the impedance. That is why it's so hard to make RCA connectors 75
    ohm, their shape and conductor spacing prevent this. BNC connectors
    are a different story, they can easily be made to be 75 ohm.

The full text can be found at:

http://www.nagysaudio.com/digitalcabletech.html


 

[Lizard_king]

Tmazz,

   Thanks for you response. I have been using this digital coax cables since the early 90s and the manufacturer who i know and am friends with tells me the BNC version will yield better SQ than than RCA one. The cable comes as BNC and he provides RCA adapters.

    Before I put the front end that I am using I did my research. I leaned about the Hi-Face and wrote the designer who told me in an email the the BNC version is better sounding that the RCA version. He even has that on his web site.

     I know a very bright Engineer who is so knowledgeable about this and he told, you should have less reflections. This confirms what the designers of the cable and Hi-face told me. The DYI forums are full of people who use BNC.

     I did make a post about this on another site and someone responded that he did that same this with his modified high end DAC and he got better performance across the board.

     I do not have an way to measure signal via a device. From what i can tell, the digital signal leaves the interface via a BNC connector and goes over the BNC XV Ultra cable to a BNC chassis mounted on my DAC and there is a 75 Ohm (i am told my the Manufacturer) coax cable going to the digital board.

     I can not speak for all systems yet it seem clear to me that BNC is a big step up in my system and a lot of other audiophiles systems as well.

Liz

[mdconnelly]

I've had excellent results with the BlackCat Veloce digital IC. 

See here: http://www.audionervosa.com/index.php?topic=2279.0

[Carlman]

   Most RCA connectors are 40 ohm.

I'd like to know which ones are "most RCA connectors".  I know of a lot of manufacturers out there.. It'd be helpful to know which is closest to 75 where you can't retrofit BNC.

However, that may just be puffery to sell his own wares.

[tmazz]

However, that may just be puffery to sell his own wares.

No!    A salesman lie to us???? I can't believe that would ever happen. 

[GaryB]

For those of you who use separates for digital, like a transport and DAC . . . Use a 75 ohm BNC . . .
SQ is much better.

I've done this mod on quite a few DACs and can also recommend it.  But I've think that it has become less important on some of the latest DACs.  DACs using the older digital receivers such as the CS8412 or CS8414 seem to be sensitive to the details of the digital cable and connector and replacing an RCA input jack with a 75ohm jack is a real improvement.

This year I auditioned the Neko Audio D100, which uses the Wolfson WM8404 receiver and the Citypulse DA-7.2X DAC, which uses the Cirrus CS8416.  For the first time, I couldn't detect a difference between the SPDIF input using Stereovox digital cable and the TOSLINK input.  Normally the TOSLINK input is considerably lower quality.  So this makes me think that the latest version of digital receivers may finally have gotten to the point where we don't need to obsess over the quality of digital interconnects and connectors.  I don't own the Neko but I do own the Citypulse, so I could do the experiment of adding a 75ohm BNC.  But it already sounds good enough that I'm not sure it's worth the trouble.

---Gary

[richidoo]

Blue Jeans Cable: http://www.bluejeanscable.com/articles/75ohmrca.htm
http://www.bluejeanscable.com/store/digital-audio/index.htm
They use these plugs:
http://www.bluejeanscable.com/pages/technicaldocs/canarercap.pdf
they fit very well, super high quality construction. But Belden 1505 coax is not so great for analog, highs are rolled.  But I use this for digital audio with good results, but true high end digital audio cables do sound better.

Canare also makes some jacks called "75Ohm Type" jacks:
http://www.tecnec.com/Attachments/ProductSpecs/RJ-R.pdf

Comprehensive Cable makes a True 75 Ohm plug. This brand, but not the 75 ohm version, is used on anticable ICs, they are decent quality.
http://www.comprehensivecable.com/connectors/7633-comprehensive-premium-true-75-ohm-rca-plug-26-awg-mini-coax.html

[Lizard_king]

Very nice GaryB.

My DAC uses a CS8414 SPDIF receiver so using BNC makes a difference!

Thanks for the info.

I've done this mod on quite a few DACs and can also recommend it.  But I've think that it has become less important on some of the latest DACs.  DACs using the older digital receivers such as the CS8412 or CS8414 seem to be sensitive to the details of the digital cable and connector and replacing an RCA input jack with a 75ohm jack is a real improvement.

This year I auditioned the Neko Audio D100, which uses the Wolfson WM8404 receiver and the Citypulse DA-7.2X DAC, which uses the Cirrus CS8416.  For the first time, I couldn't detect a difference between the SPDIF input using Stereovox digital cable and the TOSLINK input.  Normally the TOSLINK input is considerably lower quality.  So this makes me think that the latest version of digital receivers may finally have gotten to the point where we don't need to obsess over the quality of digital interconnects and connectors.  I don't own the Neko but I do own the Citypulse, so I could do the experiment of adding a 75ohm BNC.  But it already sounds good enough that I'm not sure it's worth the trouble.

---Gary
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