Using RCA cable for Coax output

[dtc]

I have a new Pro and am using one side of the included RCA cable for outputting to my dac via the coax output. I am using it partly because it fits nicely in the Pro's output and in my dac's input. Not all cables do, so this is a test phase.

Does anyone know if that is a 50 ohm or 75 ohm cable? RCA cables can be either 50 or 75 ohm or something else, so I am just curious what this one is.

Thanks.

 

[Balthazar B]

It may be neither of the above, and even the usual crappy cables from the same source that are bundled with audio devices may not match each other. You'd have to measure your own cable(s) to know for sure. Well-built and 75 ohm-compliant coax cables aren't expensive, so IMHO you'll likely be better off just getting one of those, especially if you're outputting to a good DAC.

 

[dtc]

As I said, this is a test case and I am just curious about these cables.

My guess is Wiim is shipping the same cables with each Pro. So, I am just curious if anyone knows what impedance they are.

By the way, the included optical cable is one of the few that I have tried that works at 192/24. So maybe Wimm is actually paying attention to the quality of their included cables, even if they are cheap.

 

[Mr Ee]

As it's an 'analog' rca cable it ought to be (around) 50 ohms. But who knows without measuring / checking!
As you know, it'll work, and a different cable, of either 50 or 75 ohms, may or may not sound better.
I know, I know, it's just a cable with 'digital' analog pulses going down it, but the right impedance is meant to help.
I also know that I couldn't tell the difference between a good 50 ohm analog cable and a 75 ohm digital cable when I tried both.
As I've posted before though, when I had a very cheap analog cable used in the same way you are now, it was significantly worse than the other two I just mentioned.

 

[dtc]

Thanks. One reason I got the Pro was the optical cables I tried on the Mini either did not pass 192/24 or did not fit securely in the Mini. The Pro seems to have a similar problem with fit for some coax cables. So, I hooked up the RCA for testing before potentially having to figure out what 75 ohm cable will fit correctly. It fits fine. That lead me to a simple question - does anyone know the impedance of the RCA cable that Wiim provides? Simple curiosity.

I am familiar with the pros and cons of these cables. Unfortunately, I do not have a LCR meter handy. Hence the question.

 

[Musician]

Read more here.
spdif signal is RF signal and should be treated like that.

Q. Why are S/PDIF cables specified at 75Ω?

In a digital S/PDIF cable, what exactly is the 75Ω specification a resistance measurement of?

www.soundonsound.com

”As the S/PDIF digital signal contains fundamental frequencies of 1.5 and 3 MHz, even quite short S/PDIF cables behave like transmission lines.”

 

[harkpabst]

... I do not have a LCR meter handy. Hence the question.

You cannot measure the "characteristic impedance" (also called "wave impedance") with an LCR meter, anyway. It's completely different from ohmic resistance, which will be close to zero for pretty any of those cables.

Read more here.
spdif signal is RF signal and should be treated like that.

Q. Why are S/PDIF cables specified at 75Ω?

In a digital S/PDIF cable, what exactly is the 75Ω specification a resistance measurement of?

www.soundonsound.com

”As the S/PDIF digital signal contains fundamental frequencies of 1.5 and 3 MHz, even quite short S/PDIF cables behave like transmission lines.”

That's a pretty good explanation.

 

[JohnEss]

You have to trust that the cable is built using the correct stuff. Blue Jeans has well made cables for this application...and not crazy money either. https://www.bluejeanscable.com/store/digital-audio/index.htm

 

[dtc]

You cannot measure the "characteristic impedance" (also called "wave impedance") with an LCR meter, anyway. It's completely different from ohmic resistance, which will be close to zero for pretty any of those cables.


That's a pretty good explanation.

An LCR meter is designed to measure capacitance, inductance and resistance. It is a different device than a standard multimeter.

 

[harkpabst]

An LCR meter is designed to measure capacitance, inductance and resistance. It is a different device than a standard multimeter.

That doesn't change a thing, though. You cannot measure a cable's characteristic impedance using one of them, neither a standard multimeter nor an LCR meter.

 

[KCS]

I think there are a few threads on this. I am not sure if there is a standard for the regular analog RCA cable. For coax, there two popular standards, 50 and 75 ohms. Spec for digital audio coax is 75 ohms. The question is if a regular analog RCA cable can be used. The answer is yes and no. You probably get sound, maybe even decent sound depending on the analog RCA cable. A dedicated digital audio coax will provide better sound quality. That is my experience. If you have both, try it and let the forum know how they compare. Here is the fine print. TRY THIS AT YOUR OWN RISK. I AM NOT RESPONSIBLE FOR ANY DAMAGE TO YOUR EQUIPMENT :=)

 

[Mr Ee]

A dedicated digital audio coax will provide better sound quality. That is my experience.

And yet my experience (well, if you can call comparing one analog cable with one digital cable "experience"), is that I couldn't tell them apart; from a pro into my hegel.

 

[KCS]

Score is 1 to 1. Anyone else?

 

[Fender]

Checked it right now with stuff at hand. No audible difference between Inakustik Excellence 75 ohm coax and the red one from the same line of this as nf rca. Eventually I'll try the white one later ;-)

 

[Mr Ee]

Checked it right now with stuff at hand. No audible difference between Inakustik Excellence 75 ohm coax and the red one from the same line of this as nf rca. Eventually I'll try the white one later ;-)

Yeah, you need to use the wight one!
(No, that's not a typo.)

 

[KCS]

Checked it right now with stuff at hand. No audible difference between Inakustik Excellence 75 ohm coax and the red one from the same line of this as nf rca. Eventually I'll try the white one later ;-)

Interesting. I wonder what it will sound like with two coax for analog RCA. Unfortunately I don't have two coax.

 

[Fender]

Interesting. I wonder what it will sound like with two coax for analog RCA. Unfortunately I don't have two coax.

Checked it too this morning. Incidentally I found a second identical coax cable. Again no differences. Ok, one is 25cm longer than the other. ;-)

 

[dtc]

I got a 75 ohm cable (AudioQuest Forest) and compared it to the RCA that came with the Pro and did not hear any difference. That does not confirm the impedance of the RCA cable but it does say it is potentially an option for using as a S/PDIF cable for the Pro, given the issues of finding a cable that fits the connector in the Pro. My equipment is a Chord Hugo DAC, a Pathos Classic One MkIII amp and Sonus Faber Grand Piano Home speakers. Very happy with the Pro as a front end for this system. Music sources are JRiver via DLNA, Amazon Music and Qobuz.

 

[KCS]

Below is what can be at the DAC input with and without impedance matching assuming DAC input is terminated with 75 ohms. Delay in the coax is set to 15nS for all.

Green is a 100 ohm coax cable
Red is a 75 ohm coax cable
Yellow is a 50 ohm coax cable

 

[dtc]

Yes, 75 ohms is optimal. The question is how the receiver interprets those somewhat distorted signals, which depends on the tolerances built into the receiver. Most good receivers will have a tolerance which would not see differences in those signals. But, that really does depend on how the receiver was designed, so different DACs may respond differently to these small changes in the signal. Note that these signals represent either a 0 or a 1, so the receiver can have a pretty large tolerance for non-square wave signals.