Coaxial Connection to DAC

[NAIAN]

Hey Guys,

I am thinking about buying the WiiM Pro for streaming only and I would like to connect it to my DAC.

My thought would be: WiiM Pro coaxial> Coaxial cable with BNC Adapter on it> BNC connection in DAC.

Would it be possible to buy a coaxial cable and plug a BNC connector on it to connect it with the BNC input of the DAC?
Any answer is appreciated!

 

[harkpabst]

But… the WiiM does not have a BNC out. A coax input to a BNC output is not ideal. My DAC has a BNC input and for the Pro I used the BJC 75 Ohm (Canare wire with Canare 75 Ohm RCA) which I think is a better fit. Other people I know also use this cable.

I'm afraid can't follow. In the case of @NAIAN there is a an RCA coax output connected to a BNC input on the DAC.

I see no disadvantage of RCA/BNC compared to RCA/RCA. Quite the contrary.

 

[adias]

I'm afraid can't follow. In the case of @NAIAN there is a an RCA coax output connected to a BNC input on the DAC.

I see no disadvantage of RCA/BNC compared to RCA/RCA. Quite the contrary.

The point is the coax in/out ports’ circuits are different. So I go coax to coax and bnc to bnc. Like before, I do me, you do you.

 

[mlsstl]

Best BNC feature, it's the compliance with 75 Ohm impedance required for good coupling in spdif connections.
Frequencies can reach several MHz at higher sample rate but in home use, with short length cables, due to lesser costs, prevailed the not so fitted RCA. It works anyway but rarely, 75 Ohm claimed cables are really at that impedance.
An adapter BNC RCA, raises the probability of not have correct inpedance, especially on gears with RCA inlet, where this value, can vary a lot.

Not uncommon for audio people to take information about radio and communication frequencies that are many multiples and more times the frequencies seen in digital audio (and often analog) and assume the same is a necessity. I've never had a coax connection between a streamer and a DAC not work reliably even with the cheapest of RCA cables, and never heard a difference. I know the cable believers will call me a cloth-eared fool, but that's OK. It's a big world and no surprise to me that others often have different opinions.

 

[merifon]

Mee too, never had a single problem with coax even with cheapest cables. Maybe short length helps.
Anyway I was just referring to a formal requirement for a connection that accomplishes parameters for a perfect coupling, not that this is mandatory for it to work.
Rather, it's hard for me believing that eventual errors on coax or just a slight distorted eye pattern, could be so aligned to bit sequence, in a way to modify only basses or stereo scene, or even single sound characters. It would be an hardly believable coincidence...

 

[harkpabst]

Not uncommon for audio people to take information about radio and communication frequencies that are many multiples and more times the frequencies seen in digital audio (and often analog) and assume the same is a necessity. I've never had a coax connection between a streamer and a DAC not work reliably even with the cheapest of RCA cables, and never heard a difference. I know the cable believers will call me a cloth-eared fool, but that's OK. It's a big world and no surprise to me that others often have different opinions.

The case of S/PDIF is really different. The frequency of the S/PDIF signal is not the same as the highest audio frequency contained in that signal. It's also not the same as the sampling frequency. The clock frequency must be twice the bitrate so the data can be coded into a Biphase mark code. Even a lowly (by today's standards) DAT with its 48 kHz sampling rate requires a clock speed of 6.2 MHz. See here:

S/PDIF - HwB

www.hardwarebook.info

Or have a look at the coaxial output signal of the Ultra as measured by @onlyoneme:

My Ultra tests

It's going to be a long time process, but I will try to add a new content periodically. Everything based on the pre prod device which is PCB ver 2 unit. Just one thing at the beginning, a comparison of the waveforms over the digital coax output, tested with the oscilloscope and 192 kHz sample...

forum.wiimhome.com

Take a look at the time resolution of the x-axis and convert that to a frequency value. This is not audiophile gaga madness. This is good old analogue HF signal processing, plain and simple. And that's why the S/PDIF specification calls for HF coaxial cables with a well defined characteristic impedance.

The point is the coax in/out ports’ circuits are different.

Different between cheap RCA and superior BNC? Why would that be? Both are the same single ended type of connection, following exactly the same specs. It's just that one connector type cannot guarantee the characteristic impedance (RCA) while the other can (BNC). Do you have any real world examples? Or is this something that can only be detected through listening experience? Just asking what I might not be aware of.

As far as the cable goes, having no reflection at one end is better than having reflections on both ends.

Like before, I do me, you do you.

That's fine with me. We don't have to agree on everything.

 

[mlsstl]

Even a lowly (by today's standards) DAT with its 48 kHz sampling rate requires a clock speed of 6.2 MHz.

That's fine with me. We don't have to agree on everything.

Still a big difference between a few MHz and, say the FM band which goes from 88 MHz to 108 MHz, or the broadcast TV bands which go to over 800 MHz. Haven't even gotten to the microwave and other high frequency bands yet.

But, you're right, just because I think specialized high frequency cables and connectors are overkill for audio use doesn't mean others have to agree.

 

[harkpabst]

Still a big difference between a few MHz and, say the FM band which goes from 88 MHz to 108 MHz, or the broadcast TV bands which go to over 800 MHz. Haven't even gotten to the microwave and other high frequency bands yet.

But, you're right, just because I think specialized high frequency cables and connectors are overkill for audio use doesn't mean others have to agree.

You may be able to get away with any cheap analogue RCA cable 95% of the time (maybe more), but that doesn't make deviating from the standard a recommendation. The S/PDIF specification calls for 75 ohms characteristic impedance, so my recommendation is to stick to that.

Anyway, my point is: @NAIAN, if there is a perfectly working S/PDIF connection using a cable with RCA plugs then any additional adapter to BNC can only degrade that connection. If you still want to try the BNC input of your DAC (BNC being a better match, at least in theory) go with a custom made cable instead of an adapter. And don't expect a wonder to happen.

I don't care about how microwave application and analogue FM radio might be relevant to the requirements of a digital audio interface.