Because of the way i2s and spidif are implemented. One has embedded clock and i2s has separate line.
I thought the same as 75-ohm is the SPDIF standard and I would guess 99% of people using the Digital Coax output of the DigiOne are using a 75-ohm RCA cable (marketed at 75-ohms at least - how close to 75-ohm, due to RCA geometry limitations, who knows, as you said also).
Johan has been gracious to send me a replacement DigiOne for a faulty unit - amazing customer service.
Now I’m getting a Blue Jeans Cable BNC-to-RCA cable made - not expensive and at least I reduce one RCA connection/interface in the chain.
I doubt it will make an audible difference but at least I can put the DigiOne’s 50-ohm RCA output out of my mind and reduce one RCA connection in the chain.
Would be interested to see your measurements now…
Hi Johan
I received a replacement DigiOne yesterday.
Thank you very much for your prompt replacement.
But I am busy with other things and have not yet tested the new DigiOne.
I will try to test it tomorrow.
Hi Stephane,
I’m sorry.
I will try to measure tomorrow.
Have fun and keep us updated.
No need to be sorry! I am just curious to see additional measurements, and of course read your impressions.
Hi Johan,
It turns out I have Raspberry Pi version B, which is 26pin GPIO. I know that I still could use the kali / digione with some modifications, am I correct?
After receiving my replacement board super quickly and after being surprised to read about the DigiOne’s digital coax connector using a supposed SPDIF standard 50-ohm, I replaced my BJC digital coax RCA-RCA cable with their BNC-RCA, same Belden 1800F cable.
So only the other end of my cable is now a pseudo true 75-ohm, instead of both ends (so one less RCA interface). Although iFi say their SPDIF Purifier end is 75-ohms or close to it.
And I’m now super pleased with this sound and definitely say this now beats my Digi+ Pro in my system.
After a couple weeks of proper system and brain burn in, I’ll see if the DigiOne allows me to lose the iFi SPDIF Purifier at the Dac input.
Kudos to Allo.
Thx you very much Sean .
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Little update:
I’ve made the digi one my default input now.
I had planned to use the newly released RoonAIR streaming for solo/evening listening, on the basis that it would have be ‘better’. But I have to say after a couple of weeks I’m still barely (if at all) able to discern a difference between that and the Allo.
So, since having the two inputs causes much confusion for anyone else that uses the system (“use Devialet on Ethernet for just the lounge, but if grouping use Allo on AES input” was met with gazes of ‘oh for goodness sake’) , i leave it as the permanent input, which is grouped to the kitchen most of the time. I don’t generally even bother ungrouping - setting the Allo to sync master seems to deliver on its promise and the Devialet always sounds just as good when grouped.
I would like to lose the boxes, so if the Devialet new streamer is RAAT I will definitely go that way, but meanwhile I’m very happy. 
No problem Johan, thx for the first class support and first class product.
Now that I am very comfortable replacing the HiFiBerry Digi+ Pro in my system, I am looking to remove the downstream iFi SPDIF Purifier - in particular for it’s galvanic isolation.
Of course I will let my ears make the final decision but can you share more info on the digital isolation of the DigiOne?
I understand the power and data lines are isolated - this includes the ground plane?
Many thanks again, Sean
The Hifiberry Digi+ has now gone from my system too in favour of the DigiOne. I will try the USBridge too before deciding which to use in the main system.
As an aside I am Building another complete system for my daughter using a RPi3 with Kali and Piano 2.1 in dual mono mode. I have to say is sounds pretty good!
There are 2 ways to isolate the spidif signal
- Use a transformer in the end. Unfortunately transformer distorts signals.
- Use digital isolator + isolated DC (ground is isolated)
We chose the latter.
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Thanks, since power, ground and data are all isolated and then reclocked, I should be able to remove the iFi SPDIF Purifier from the chain.
I’ll let me ears and brain adjust to this new fantastic sound first, then remove the iFi after a couple of weeks to test.
Hi, all. Will the BNC be better than RCA?
Only from my limited experience, I would use a Blue Jeans Cable’s BNC-RCA cable if your DAC only has digital RCA input. There’s a high chance your DAC’s digital RCA input is optimised for 75-ohm (optimised, not true 75 ohm, as discussed earlier up in the thread).
The DigiOne’s digital RCA output is optimised for 50-ohm.
I’m definitely not an expert though. Just personal experience with my system.
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Theoretically yes. BNC is a true 75Ohm impedance and physical connection is slightly better .
Practically , depends on your particular system and how RCA/BNC is implemented at the DAC side.
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Thank you Sean! It’s really useful!
Now I know why there’s a bnc output on Digione and hifiberry digi+ pro support it.
So, even use a BNC-RCA cable would be better than RCA-RCA, right?
In my system, yes that’s the direction I went and am very happy.
It can vary between each system of course.