MDAC First Listen (part 00110111)

[jirij]

I wonder have they have achieved galvanic isolation for USB 3 data rates.

Galvanic isolation means two totally isolated electrical domains, and is usually done optically or inductively.

To do that at USB 3 data rates you would probably have to use a fibre optic link, as USB opto-isolator and inductive isolator components are only USB 1.1 compliant.

Well, it depends. It is in theory possible and was done in the past (see one Corning USB3.0 extender - yes, it had metallic wires inside, but those were for power), just that none of these are available in off-the-shelf chips and if John was to do something like that from scratch, he would have intellectual property claims up his a** from all the major chip manufacturers.

IFiAudio have announced the iGalvanic3.0 which they claim offers galvanic isolation, USB regeneration and clean power. It works at all speeds so hi res stuff should be no problem and is USB3.0 and USB2.0 compliant. Last time I looked the DETOX wouldn't do hi res and isn't USB3.0 so the ifiaudio thing looks like a more than serious competitor.

I thought "hi-res" usually means 96k/24bit or more, in which case even USB1.1 is enough. USB1.1 is 12Mbit and 96k*24bit*2ch is ~4.6Mbit, meaning ~37% of the full interface bandwidth is usable. Even if we assume the same is true for USB2 (realistically, it will probably be less), that gives you 480Mbit*0.37 / 2ch / 24bit = ~3788khz of sampling rate, which I consider to be "hi-res" enough for most people (industry-wise, we are at 768khz max).

 

[stephengrenfell]

Well, it depends. It is in theory possible and was done in the past (see one Corning USB3.0 extender - yes, it had metallic wires inside, but those were for power), just that none of these are available in off-the-shelf chips and if John was to do something like that from scratch, he would have intellectual property claims up his a** from all the major chip manufacturers.

Sure it could be done - using fibre optic. Corning do optical USB 3.0 extenders (I almost bought one). But as you say it also has copper wires end–end (to power the far end optical converter) and so is not a galvanic isolator.

 

[BigDog]

Sure it could be done - using fibre optic. Corning do optical USB 3.0 extenders (I almost bought one). But as you say it also has copper wires end–end (to power the far end optical converter) and so is not a galvanic isolator.

You are correct re the Corning. When the product was first announced, I spoke to their technical people about the galvanic isolation and they insisted it was. However, when the product was actually released, I followed up and was told that there was a thin copper wire head to tail providing power to the receiver.

However, if you want galvanic isolation and source-to-DAC separation of more than 5meters, there is a product from Adnaco <http://www.adnaco.com/products/s3a/>
which has a receiver powered by a wallwart thus offering true galvanic isolation. I replaced the walwart with an LPS so as not to re-introduce noise at the DAC end. Not inexpensive but I have been quite happy with it.

This of course was before the proliferation of devices defeating the USB 5V for DACs which allow this such as mine or providing a clean source, e.g., double headed cables with dedicated power supplies.

 

[Rune]

I wonder have they have achieved galvanic isolation for USB 3 data rates.

Does it matter?

No not really because USB 2 has enough bandwidth for even the highest sample rates and are there actually any DAC that has USB 3.

So rather pointless in a DAC/Straamer context

 

[AndyU]

Does it matter?

No not really because USB 2 has enough bandwidth for even the highest sample rates and are there actually any DAC that has USB 3.

So rather pointless in a DAC/Straamer context

According to JohnWs post that I linked to earlier, the DETOX will only galvanically isolate to USB1.1 therefore a maximum of 24bit/96kHz. So it does matter if you want to play higher res than that and get galvanic isolation - you won't with the DETOX and you will with the iFiAudio device. Neither actually exist yet. Here's what JohnW said about the DETOX

The Hub device used has two High Speed USB 2.0 480Mbps outputs. The first is directly RF Filtered and avaible as a USB 2.0 non isolated output.

The second output from the final USB Hub, RF filtered and fed to a USB 1.1 (12Mbps) Galvanic isolation device, RF filtered and then output'ed on the second USB connector (Galvanically isolated, but limited to a maximum supported data rate of 96KHz 24 Bits).

 

[Rune]

Why are you so sure that galvanic isolation is the most important function of the Detox?
My understanding is that it is not.

 

[AndyU]

Why are you so sure that galvanic isolation is the most important function of the Detox?
My understanding is that it is not.

I am not at all sure that galvanic isolation is the most important feature of the DETOX. I just posted about the ifiaudio thing in the context of someone wondering what the competitors to the DETOX might be. Seems to me they might be competitors. Of course, they both need to actually exist first ..

 

[stephengrenfell]

Does it matter?

No not really because USB 2 has enough bandwidth for even the highest sample rates and are there actually any DAC that has USB 3.

So rather pointless in a DAC/Straamer context

I was simply curious how they achieve galvanic isolation at such high data rates for a small cost.

 

[stephengrenfell]

Why are you so sure that galvanic isolation is the most important function of the Detox?
My understanding is that it is not.

No one has said that galvanic isolation is the most important function of the Detox.

Indeed there are other essential features.. like successive USB buffering to reduce the sonic effects of the bursty USB data stream, isolated clock domains for each buffer stage, clean and isolated power supply rails for each buffer stage to avoid injecting noise onto the USB data that goes to the DAC, , being able to clock lock the USB data stream output to the DACs master clock, for example…

 

[stephengrenfell]

However, if you want galvanic isolation and source-to-DAC separation of more than 5meters, there is a product from Adnaco <http://www.adnaco.com/products/s3a/>
which has a receiver powered by a wallwart thus offering true galvanic isolation. I replaced the walwart with an LPS so as not to re-introduce noise at the DAC end. Not inexpensive but I have been quite happy with it.

In the end I solved my distance problem by buying a mac mini + linear psu + non pwm cooling fan control, and putting it next to the mdac instead of using an imac 20m away. Not cheap either but I'm happy with the result.

 

[BigDog]

Does it matter?

No not really because USB 2 has enough bandwidth for even the highest sample rates and are there actually any DAC that has USB 3.

So rather pointless in a DAC/Straamer context

Selling products making reference to USB3.0 for audio, IMO, are like selling ethernet cables making reference to Cat7 (or 8). Inquiring to Blue Jeans Cable about the latter, I was told that while a standard exists it has no relevance for audio. Plus, my source indicated that neither 7 or 8 cable would like fit in an R45 connector.

Interestingly, after inquiring about shielded ethernet cables, i.e., STP, S/STP, I was also told that they may actually be worse for audio than a benefit.

 

[stephengrenfell]

Interestingly, after inquiring about shielded ethernet cables, i.e., STP, S/STP, I was also told that they may actually be worse for audio than a benefit.

If the ethernet cable were to be used for a USB extender - then that might be correct as the shield would provide an end-end 'ground' connection, and it would depend on how the extenders deal with grounding the shield.

However if the Ethernet cable is used to provide a networking connection and the shield grounding is dealt with correctly (at the hub for example) it shouldn’t be relevant. On the other hand if the shield grounding isn’t done somewhere then the shields will float and potentially introduce noise (as may be the case if shield continuity and grounding is not provided by the sockets at the hub).

 

[kennyh]

Maybe a daft but a deadly serious question nevertheless. Why is USB needed nowadays for streaming and listening to music?

Did away with it a while back and for the better.

 

[stephengrenfell]

Maybe a daft but a deadly serious question nevertheless. Why is USB needed nowadays for streaming and listening to music?

Did away with it a while back and for the better.

It's not a daft question. The answer is because it's the easiest way to contact a computer to a DAC. And many folks like using a computer to run their player software as this offers the most flexibility.

If you use a dedicated streamer with a built-in DAC then it may have WiFi or Ethernet connectivity. But then you maybe constrained to use whatever software it will work with.

What did you use instead ?.

 

[kennyh]

Hi Stephen. I use Picore now. If I ever use the MDAC I feed it with a RPI/DIGI board.

However the game changer is the Allo piano dac with Kali clocker. One Cat 6 ethernet in 2 x RCA's to pre amp and an IFI powering it.

Run the MDAC via USB from a PC and the difference for the worse is not subjective.

We had a few "mini PFM" dac bake off's a while back with some surprising results.

 

[kennyh]

To take it one step further, and to maybe glean advice on what I'm missing here.

I've been following this thread since John reworked my MDAC with its new caps etc. I would have maybe jumped in too but can never get a good grasp on what's what in order for me to support it.

For instance, with the news that an RPI board is to be fitted in the new MDAC (am I correct there?) then I'd have thought the streaming capability would be using a programme like picore/roon/volumino etc to enable streaming of things.

The laptop then surely only becomes the control to link it to the net and access the server. Why is a USB connection needed?

Therefore to my mind why the year in year out fuss over detox/USB etc.?

As I say I'm probably missing a huge point here so bring this up to be educated on my beliefs as they stand.

Cheers,

 

[stephengrenfell]

Hi Stephen. I use Picore now. If I ever use the MDAC I feed it with a RPI/DIGI board.

However the game changer is the Allo piano dac with Kali clocker. One Cat 6 ethernet in 2 x RCA's to pre amp and an IFI powering it.

Run the MDAC via USB from a PC and the difference for the worse is not subjective.

We had a few "mini PFM" dac bake off's a while back with some surprising results.

So how do you connect your Allo piano dac to the Raspberry PI via I2S ?.

MDAC2 has a RPI CM3 buit-in streamer option.

Some tests were done by John a while back to compare the Raspberry PI CM3 connected to the DAC via I2S and USB. I2S had significant limitations over USB at higher data rates, and far as I can remember doesn’t support native DSD – I2S can only support PCM.

 

[kennyh]

So how do you connect your Allo piano dac to the Raspberry PI via I2S ?.

MDAC2 has a RPI CM3 buit-in streamer option.

Some tests were done by John a while back to compare the Raspberry PI CM3 connected to the DAC via I2S and USB. I2S had significant limitations over USB at higher data rates, and far as I can remember doesn’t support native DSD – I2S can only support PCM.

Hi Stephen, the Kali sits between the dac and RPI and is supposed to do the i2s bit I was told.

Don't know how the IQ set up works though which is also excellent with no need for USB once more.

 

[stephengrenfell]

then I'd have thought the streaming capability would be using a programme like picore/roon/volumino etc to enable streaming of things.

I recall the supplied SW build for the MDAC2 streamer is to be Volumino. Beyond that anyone can install what they want, but bear in mind some folks might find that easy to do, others less linux savy not so. Horses for courses.

The laptop then surely only becomes the control to link it to the net and access the server. Why is a USB connection needed?

Not everyone wants, or will use, the built-in streamer. So USB connectivity offers an alternative that they might prefer. It’s a question of personal choice rather than what’s technically the best / easiest.

 

[Rosewind]

Interesting product, Kenny.