SPDIF to AES/EBU conversion

[SGK]

Howdy

I'm a novice to electronics but learning.

I have an ESI Juli@ XTe sound card from which I have jumpered a short coaxial cable to an RCA jack to bypass the breakout cable for S/PDIF out. I'm now thinking about replacing this with an AES/EBU connection and want to make sure I understand how to implement this properly.

From here I read the following (My underlining emphasis):

AES3id or S/PDIF to AES3

This conversion only requires impedance matching since the levels are smaller than AES3, but compatible. No satisfactory resistor-only network exists to convert between AES3id or S/PDIF and AES3 even though one appears in the AES3id document. While the network given matches the impedance, it does so with an attenuation of the input signal, running the risk of making it too small for the AES3 receiver, and it does not create the balanced 110-ohm lines that an AES3 receiver needs. Therefore it is recommended to use a transformer for this conversion as shown in Fig. 4. Note that this adapter is identical to that shown in Fig. 3, only driven backwards. Using the store-bought converter with a male-to-female adapter allows it to be fully bi-directional _ or build your own using the recommended transformers. BUT DO NOT FORGET that the levels coming out of an AES3 transmitter are too large for the typical AES3id or S/PDIF input so you must add the attenuator. Going the other way you do not need the attenuator since all AES3 receivers can handle the smallest in-spec AES3id or S/PDIF output signal as long as a minimum of 200 mV arrives.

I take it from the above that implementing this connection is as simple as sourcing and wiring a transformer. The article references a Schott P/N 22523 through hole transformer for this purpose but I've not been able to find a source for this. This article recommends a number of suppliers of transformers but I've not yet found a source for these either. I have found a source of Lundahl transformers that claim to do the same.


Am I on the right track here?


Regards


Steve

 

[SGK]

84 views and no takers?

 

[SY]

There's a few ways to take care of the levels- there's also some subtle code differences, but they aren't of great concern for home audio use. Here's the schematic of the adapter that I built- the output transformer is a standard inexpensive Murata unit that I got from Mouser or Digikey (can't remember which).

 

[SGK]

Hi. Thanks for the response.

Are the hex inverters in your schematic for the "subtle code differences"? I will take a look for the transformer.

I guess one thing in the back of my mind re this conversion is whether a SPDIF to AES/EBU conversion without the higher voltages of the later is worth doing - if I understand the differences between the two correctly. Is getting a 110 Ohms impedance any gain over straight SPDIF?

 

[SY]

No, they're just level shifters. I don't worry about the code differences since this isn't a studio installation. No, there's no particular advantage to AES/EBU over SPDIF in a home installation, they're just slightly different standards.

More reading:

http://www.nu9n.com/images/AES3-SPDIF-notes.pdf


and for nitty gritty:

http://tech.ebu.ch/docs/tech/tech3250.pdf

The differences in the two standards' code is the channel status bit, usually a non-issue.

 

[gazza49]

http://www.bodziosoftware.com.au/AES_EBU_Converters.pdf

 

[SGK]

SY, I think your first link is the same article I posted to. As to the differences between SPDIF and AES/EBU in a "home installation" there is still a strong preference for AES/EBU in the high-end segment. I guess my first question is whether people prefer the latter because the voltage signal is stronger. I'm trying to understand what you mean by "level shifters". You bring the voltage up to an AES/EBU equivalent?

Gazza49 - I'm talking about going the other way. If going from AES/EBU to SPDIF then the levels need to be attenuated and the impedance corrected. Here I'm talking about taking SPDIF from the Juli@ card and converting it to AES/EBU. Note that this is exactly what Bryston did with their BPD-1 and 2. I'm just not sure if all they did was provide the impedance transformer and leave it at that.

 

[SGK]

Also, isn't the turns ratio on the Murata DA103 transformer 1:1? How is impedance managed? (Sorry if these are basic questions given you have provided your schematic.)

 

[SY]

I'm trying to understand what you mean by "level shifters". You bring the voltage up to an AES/EBU equivalent?

Yes. Additionally, the output impedance is raised to the AES/EBU standard. The transformer is 1:1 because the impedances are already correct, all it does is provide galvanic isolation.

 

[gazza49]

i cant answer your questions but ,this item goes both ways

What's small, square, roughly the color of the Cookie Monster, and could quite possibly save your sanity? Give up? Why, it's the Hosa CDL-313 S/PDIF to AES/EBU converter box. Seriously, have you ever had the frustration of trying to hook up a piece of gear that outputs AES/EBU to your interface. It's about as easy sticking a round peg into a square hole... while wearing greasy oven mitts. Most high-end interfaces have ADAT light pipe and S/PDIF inputs, but AES/EBU? Yeah right! That's where the CDL-313 comes in. Just hook up your AES/EBU and your S/PDIF cables, and you're golden! You can even go the other way around too. And we're not talking about some crippled digital audio either - straight up 24-bit/96kHz performance here! So make your life easier, and pick up a Hosa CDL-313 S/PDIF to AES/EBU converter box before you end up beating your head against a wall.

 

[SGK]

Yes. Additionally, the output impedance is raised to the AES/EBU standard. The transformer is 1:1 because the impedances are already correct, all it does is provide galvanic isolation.

got it. I will spend more time with your schematic. I guess one would have to make this up on protoboard at a minimum.

 

[SGK]

Yes it does. In a box that would be difficult to wire into my audio server unless I pulled it to pieces. I'm intrigued by the advertisement's reference to 96kHz. Why not 192kHz which is what my ESI Juli@ sound card is capable of?

 

[SGK]

This is probably a super basic question but am I right that U1a-f is all one component and that you have supplied 5V via USB port? I will have to study the data sheet and see if I can figure out what's going on. I think I may be slow… 🙂

 

[SY]

Yes, I paralleled a bunch of sections since it's a hex unit and they're there anyway. That drops the output impedance and lets the series resistors dominate it. And yes, I did it on a small protoboard.

 

[SGK]

Any pics?

This is probably above my skills for now but I will persevere.

 

[SY]

Here ya go.