SPDIF Transport: Allo Digione or Allo Digione Signature Bundle (seeking opinions)

[shyamv]

Hi Shyam,

Yes i can connect the topping d10 directly to amp aswell. but i purchased it recently mainly for conversion. my original dac is still the non-oversampling muse mini as it sounds very good since it has the philips chip tda1543.

the rpi was introduced in the chain few months back for airplay reasons. i was initially using the headphone out, then i had got i2s hifiberry dac in the expectation that it will improve the sound. however that did not happen. then i realized i can get sound from usb out aswell. i then attached some other pcm2704 based usb to spdif convertor but it did not sound good. then i read about topping d10 and purchased it. and now recently i came to know in detail about allo digione and usbridge which look promising.

Got it. If you want to continue using Muse Mini as your primary DAC, then a cleaner solution for AirPlay and USB audio would be Allo Digione as your SPDiF transport. I would not recommend Allo USBridge as your DAC has only SPDiF coax and optical inputs. You already have a RPi. So, just buy a Digione HAT for ₹5.5k , install Moode or Volumio on RPi3, connect your Digione to Muse Mini over Coax digital and you are all set. You can take out Topping D10 out for this chain. Digione takes the i2S signal from RPi and coverts to SPDIF coax or BNC and this is a much cleaner path than headphone or USB A from RPi.

Yes, you would need a proper 75Ohm coax SPDiF cable. The issues you are observing is very definitely due the wrong cable. Typically, Coax has lower jitter than optical so you get cleaner signal if your source is noise-free which is what Allo Digione will deliver. If you have HifiBerry Digi or Digi+, you can use this also as a SPDIF transport but Allo Digione is better.

 

[amit11]

The issues you are observing is very definitely due the wrong cable. Typically, Coax has lower jitter than optical so you get cleaner signal if your source is noise-free which is what Allo Digione will deliver.

My confusion is how do i determine if i am using wrong cable for coax without purchasing a new one? Somewhere i had read that, most rca cables , example the red and white ones which we use for tv audio, are also by chance 75ohms. so i am assuming the mogami 2803 or the normal rca cable which i am using is also 75ohms by chance, or somewhere near it and it should not cause any issue.

Assuming above is true, is it possible that in my system neither the sender nor the receiver is having galvanic isolation for coax and noise is creeping from the sender? and thats why the brightness...

 

[raghupb]

one more thing for coax. i do not have a proper coax cable of 75 ohms. i am using rca cable for coax purpose. the rca may or may not be 75ohms exactly. i tried normal rca cable and mogami 2803 also. in both cases the coax was sounding less warm compared to optical.

Check if you have an old component video cable (the Y-Cb-Cr types)
They will work for digital coax
Cheers,
Raghu

 

[Weathered]

https://hifimart.com/product/mogami-gold-w2964-spdif-75-ohm-digital-cable-rca-to-rca-html/ - This one is a good 75 ohm cable.

 

[amit11]

Check if you have an old component video cable (the Y-Cb-Cr types)
They will work for digital coax
Cheers,
Raghu

Yes i tried with that aswell. The red/white one combo. Inspite of that the coax is sounding slightly brighter compared to optical. It is bcos noise might be creeping from sender to receiver and there is no galvanic isolation?

 

[raghupb]

Yes i tried with that aswell. The red/white one combo. Inspite of that the coax is sounding slightly brighter compared to optical. It is bcos noise might be creeping from sender to receiver and there is no galvanic isolation?

Red/White is vanilla RCA. The termination is around 50 ohms or something.
Component video cables are 75 ohm termination, and were meant to carry high speed digital signals.

BTW, Allo's claim is that they clean up I2S from RPi board in their HAT.
Design wise, using LDOs is the way to go for such clean up.
I say this from EE/board-design experience (non audio stuff)
They seem to have got it right at a fair price point.

Cheers,
Raghu

 

[amit11]

BTW, Allo's claim is that they clean up I2S from RPi board in their HAT.
Design wise, using LDOs is the way to go for such clean up.

Cheers,
Raghu

So if the coax output from allo is already noise free, then as such there is no requirement to have galvanic isolation on the receiving DAC side, right? Asking bcos my muse mini dac I assume does not have such a feature.

 

[Kannan]

https://hifimart.com/product/mogami-gold-w2964-spdif-75-ohm-digital-cable-rca-to-rca-html/ - This one is a good 75 ohm cable.

That is not the right connector to terminate a coax cable for digital audio duty. But is ok for analogue RCA (ie as analogue interconnect)

 

[jls001]

... so i am assuming the mogami 2803 or the normal rca cable which i am using is also 75ohms by chance,

IIRC, 2803 is a 50 Ohm coax cable.

Even if you have a 75 Ohm coax cable, if the termination is RCA then it won't be a proper 75 Ohm cable unless one chooses a 75 Ohm RCA plug (like some Canare models). The condition that a finished coax cable will be true 75 Ohm characteristic impedance is:
1) the coax cable is 75 Ohm
2) the plug is a true 75 Ohm

The distance between the core wire of the coax and the shielding determines the characteristic impedance of that cable. If the shield is split in any way, like it must be for soldering the shield to RCA to ground/barrel of RCA, then the strict geometry is broken, and the characteristic impedance of the finished cable will no longer be 75 Ohm.

 

[Kannan]

Canare RCap is one of the better connectors for Digital coax. Even that too will not spec 75 unlike the BNC.
But again it matters more for transmission of digital video and multichannel audio due to the need for a wider bandwidth than digital audio.

That said it is better to spec the phono (RCA) connectors as close to 75 as possible.
There are ofcourse few other options than the RCap, and a little cheaper aswell.

Another aspect is that RCA type digital type coax cables are excellent for analogue duty aswell.

Kannan

 

[raghupb]

So if the coax output from allo is already noise free, then as such there is no requirement to have galvanic isolation on the receiving DAC side, right? Asking bcos my muse mini dac I assume does not have such a feature.

COAX will never be noise free. The noise levels will be minimal so as to not make an impact when passing through the rest of the chain.
What Allo promises is, that digital noise from RPi will not creep into the audio output.
The HAT is specifically meant to suppress and clean up this noise.
And of course very low jitter.
In fact on the Sig version, they have dirty board, clean board and 2 power supplies.

So you may benefit from this and the DAC does not need to do anything fancy.
The DAC in my chain is a basic one, but dropped in from Parasound's premium line.

Cheers,
Raghu

 

[jls001]

One way of staying 75 Ohm is to buy good BNC-BNC coax cable of desired length, then use BNC to RCA adapters at both ends.

But having said that, I would say that it's okay to use most RCA-RCA cables. Yes, transmission line theory says that you won't be able to get the maximum signal across to the destination because of the impedance mismatch, but maximum signal transfer is hardly the goal in audio SPDIF connections. The timing will also be messed up compared to a true 75. But seeing that practically every CDP and DAC uses RCA for coax, I guess the degradation is not substantial enough to warrant sticking to BNCs.

 

[Kannan]

BNC to RCA adapters

This too is at best a jugaad. BNC to RCA though makes sense. But I have seen many go RCA to BNC which has no advantage

 

[raghupb]

Actually Digione has BNC option. So one would need a BNC/Coax only at DAC, if needed.
Cheers,
Raghu

 

[amit11]

But having said that, I would say that it's okay to use most RCA-RCA cables.

so if coax is lets say 50 ohms instead of 75 ohms, can it create sound quality issues? like in my case i find coax to be slightly brighter compared to optical in the same dac.

 

[amit11]

One way of staying 75 Ohm is to buy good BNC-BNC coax cable of desired length, then use BNC to RCA adapters at both ends.

But having said that, I would say that it's okay to use most RCA-RCA cables. Yes, transmission line theory says that you won't be able to get the maximum signal across to the destination because of the impedance mismatch, but maximum signal transfer is hardly the goal in audio SPDIF connections. The timing will also be messed up compared to a true 75. But seeing that practically every CDP and DAC uses RCA for coax, I guess the degradation is not substantial enough to warrant sticking to BNCs.

I had come across yesterday one of your thread which is 4 years old. it is related to galvanic isolation using pulse transformer module for a coax cable.

https://www.hifivision.com/threads/improving-digital-coax-cable-by-galvanic-isolation.62277/

my thinking is in my setup, the coax output from topping D10 might be injecting some noise which is creeping inside the DAC and making it sounding slightly brighter.

 

[jls001]

so if coax is lets say 50 ohms instead of 75 ohms, can it create sound quality issues? like in my case i find coax to be slightly brighter compared to optical in the same dac.

Your 2803 is NOT 50 Ohm in its present configuration.

2803 is inherently on the bright side. Please try some other cable you have.

My experiments with galvanic isolation on coax cable was mainly an experiment. It will block all unwanted DC components and impulse type fast transients but any AC noise component which comes from the source will be passed through as is.

 

[Madhu75]

I am using two Mogami cables 2534 rca Cable Connecting from Denafrips dac Ares 2 to amp and Mogami 2965 which connects laptop USB to Denafrips dac Ares 2 USB. Very good results. I am not so much aware about ohms etc but practically i find sound very rich.

 

[shyamv]

Canare RCap is one of the better connectors for Digital coax. Even that too will not spec 75 unlike the BNC.
But again it matters more for transmission of digital video and multichannel audio due to the need for a wider bandwidth than digital audio.

That said it is better to spec the phono (RCA) connectors as close to 75 as possible.
There are ofcourse few other options than the RCap, and a little cheaper aswell.

Another aspect is that RCA type digital type coax cables are excellent for analogue duty aswell.

Kannan

Canare RCAP-C53 is good connector for digital coax. I use this with Belden 1694A cable and great value for money. I found this better than Mogami W2964.

 

[shyamv]

Actually Digione has BNC option. So one would need a BNC/Coax only at DAC, if needed.
Cheers,
Raghu

I wouldn't bother with BNC-RCA digital coax in Digione setup. A good quality BNC-RCA digital coax will cost more than RPI+Digione put together and no matter what, I am not a proponent of spending more on cables than the equipment itself. A good 75Ohm RCA coax cable with right terminations around 1-2K should work well.