Author Topic: Getting from USB to AES3 without breaking the bank  (Read 450 times)

Offline Rotten Johnny

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Getting from USB to AES3 without breaking the bank
« on: February 23, 2017, 08:36:48 AM »
Most DACs seem to include an AES/EBU input but when it comes to using PC/servers for streaming these days USB has become the flavour of the day.  I recently found a (somewhat convoluted) way to get it done.

Put a USB to coax converter at the receiving end of the USB stream, pop a RCA/BNC coax cable between the converter and pop a Neutrik Digital Audio Impedance Transformer (NADITBNC-M) between that and your DAC.  Voila, you have an AES3 input.  Not sure there's any sonic advantage, will do a little listening via the Yggy into the Joty into HD800 to see whether there's any appreciable change one way or the other.



The alternative is to buy a USB to AES3 converter for an ungodly sum of money.

Perhaps pwatts could share his thoughts on using a convoluted signal stream such as this?
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Offline Rodney_gold

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Re: Getting from USB to AES3 without breaking the bank
« Reply #1 on: February 23, 2017, 02:59:08 PM »
I just used a rca to xlr adaptor after my usb to spdif converter

devialet uses that method too to join a master amp to a slave

https://help.devialet.com/hc/en-us/articles/203402291-How-to-make-the-SPDIF-to-AES-EBU-cable-by-myself
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Offline handsome

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Re: Getting from USB to AES3 without breaking the bank
« Reply #2 on: February 23, 2017, 03:44:05 PM »
AES and SPDIF are essentially the same thing: SPDIF is single ended AES is balanced both carry the same signal though. So Rodney's/Devaliet's suggestion will work but it is not true AES it is not balanced, just SPDIF on one pin of an XLR. Your solution of using a transformer is a true SPDIF to AES conversion, I would suggest using as short as possible SPDIF cable to the transformer but it appears that SPDIF cable is captive.

Offline Rotten Johnny

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Re: Getting from USB to AES3 without breaking the bank
« Reply #3 on: February 23, 2017, 03:52:41 PM »
It's my intention to use a very, very short coax cable from the uDSD to the transformer, I thought I'd test it first before making up a short cable.
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Online scrarfussi

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Re: Getting from USB to AES3 without breaking the bank
« Reply #4 on: February 24, 2017, 12:44:40 AM »
It's my intention to use a very, very short coax cable from the uDSD to the transformer, I thought I'd test it first before making up a short cable.
there is an article somewhere about using short coax cables
reflections etc  :whistler:
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Offline handsome

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Re: Getting from USB to AES3 without breaking the bank
« Reply #5 on: February 25, 2017, 07:50:29 AM »
indeed but the rotten man wants to send his signal via AES. having a long SPDF cable then converted to AES plus further length achieves nothing. Ideally the AES convertor transformer should be attached to the sending device - since the thought of that kind of surgery usually scares the heck out of folk as short an external connection as possible is the only feasible way. Then again those transformers are by nature very small......

As to them pesky reflections, to eliminate them you need to be sure your sending and receiving connectors are truly 75ohm impedance and your cable is too, assuming a true 75 ohm output impedance of your device then, there will be no reflections. A 75 ohm transmission line (your cable) terminated in 75 ohms can be any length whatsoever (even infinite) and will always present a 75 ohm impedance to the (75 ohm) source guaranteeing zero reflections. Unfortunately very few RCA connectors are true 75 ohm impedance terminations......

Offline Rotten Johnny

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Re: Getting from USB to AES3 without breaking the bank
« Reply #6 on: February 25, 2017, 08:12:53 AM »
Therein lies the rub, I haven't found a USB to coax converter that has a 75Ω output...they generally have a regular RCA on the output side.
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Offline Hi-Phibian

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Re: Getting from USB to AES3 without breaking the bank
« Reply #7 on: February 25, 2017, 08:32:46 AM »
As the whole chain is a little unknown re exact impedance and without a TDR or similar it's hard to know I think the only way to know re reducing reflections and audible effect would be to compare long and short. 

Jocko Homo I think it was explained at some point that from a dimension spec point of view an RCA can not be 75 ohm at all unless one starts reducing the outer ring to less than 360 degrees. This I suppose has its own issues again.







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Offline handsome

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Re: Getting from USB to AES3 without breaking the bank
« Reply #8 on: February 25, 2017, 10:57:48 AM »
Canare made a claimed 75ohm RCA. And so did WBT  - no doubt at the cost of an AES equipped  DAC or two. Either way if you want all the benefits of AES the shortest cable to your transformer is the way. But do report on the results

Offline Agaton Sax

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Re: Getting from USB to AES3 without breaking the bank
« Reply #9 on: February 25, 2017, 11:05:19 AM »
My little experience. I used a M2Tech Hi face usb-sbdif converter with  a rca connector to the dac. I received a new custom digital cable. The DAC would not lock on to the signal. Thought the converter had fallen and was faulty and bought a new one-still no lock. Tested the cable -it was fine. Lots of experiments later I remain disappointed at the enormous sonic differences  spdif cables make. That is subjective make of it what you want.

Facts as I understand them: No RCA connector can be 75 ohm. The alternative BNC connector is normally 50 ohm unless one use a very specific 75 ohm BNC connector for all female and male connectors. Superficially these look the same as the 50 ohm ones but there are differences. Consensus is that one must use the correct cable with correct termination for optimal performance. You can not  use any analogue cable.

507hohm by jdza, on Flickr

The same goes for AES xlr able. Any old balanced audio cable will not do. It must be 110 ohm. Do not use audi0cable for digital-. So they say

Offline pwatts

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Re: Getting from USB to AES3 without breaking the bank
« Reply #10 on: February 25, 2017, 12:31:02 PM »
If the S/PDIF to AES converter uses a (good) transformer, I don't see why it would necessarily pose a problem. There even are some potential advantages, but whether the tradeoff of more complicated signal path vs. these advantages are worth it depends on the entire chain.
Having a good transformer in the path will offer two advantages:
1) isolate the incoming signal if not already isolated
2) filter RF noise if the transformer is well designed to operate only in the appropriate band
3) jack up the signal swing. S/PDIF is designed for 1Vpp when terminated, wheras AES can go much higher (up to 10Vpp). This of course leads to improved CMRR and higher noise immunity, and this gain is had for free when using the correct transformer and termination.

On the other hand, cheap transformers have high parasitic capacitance and bandwidth limitations: often a regular Ethernet 'pulse' transformer is used which is great for Ethernet speeds, but S/PDIF works at lower frequencies too and therefore they're not as great. Choosing the correct transformer is therefore rather important and only a few companies make them. Scientific Conversion, has some of the best, but hard to find and at a premium price. For AES to S/PDIF one will anyway need a custom transformer dedicated to the job, or using two and an active buffer.

I'm not sure if true 75ohms is really that important TBH, especially since I haven't seen any PCB's that accurately follow the transmission line similarly all the way to the receiver IC. This is especially true with products where the I/O module is separate from the mainboard, where 2 PCB layers alone are enough to get the job done, but not maintain the impedance. It's not that it cannot be done (otherwise measuring gear or even a DSTV decoder would never work), it's just that nobody bothers.

AES uses XLR which definitely is not 110ohms, and many folks prefer AES over BNC S/PDIF which (can) be full 75ohms.

Offline pwatts

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Re: Getting from USB to AES3 without breaking the bank
« Reply #11 on: February 25, 2017, 12:33:15 PM »
there is an article somewhere about using short coax cables
reflections etc  :whistler:

If using only a passive transformer then the short cable will not matter since the total transmission line of S/PDIF + AES is the total length. If there was an active buffer in the converter it's different.

Offline Rotten Johnny

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Re: Getting from USB to AES3 without breaking the bank
« Reply #12 on: February 25, 2017, 12:34:15 PM »
^^^ could you translate all that to English in the context of what I've done above?

Also, I understood AES3 requires a 110Ω cable to be used?
Audiophile: There is almost no other group that prides themselves more on wasting good money on utterly worthless ****, and then trying to furiously blow smoke up their own ass to justify it.

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