• Registered: 2022-10-26
  • Posts: 21

Topic: XLR to RCA AES/EBU cable

According to the ADI-2 manual

https://www.rme-audio.de/downloads/adi2dacr_e.pdf

such cable should have pin 1 wire floating on the RCA side

"Using a simple cable adapter XLR to RCA, an
AES/EBU signal can be received too. To achieve
this, pins 2 and 3 of a female XLR plug are connected individually to the two pins of a phono plug.
The cable shielding is only connected to pin 1 of the
XLR - not to the phono plug."

but on the other side, according to the UCX II manual

https://www.rme-audio.de/downloads/fface_ucx2_e.pdf

such cable should have pin 1 grounded on th RCA side

"To receive signals in AES/EBU format, an
adapter cable is required. Pins 2 and 3 of
a female XLR plug are connected individually to the two pins of a phono plug. The
cable shielding is connected to pin 1 of the
XLR and the ground contact of the phono
plug."


Why there is such a difference?

2 Reply by ericseaberg (edited by ericseaberg 2024-01-01 17:19:16)

  • From: San Diego, CA
  • Registered: 2017-09-18
  • Posts: 73

Re: XLR to RCA AES/EBU cable

What you should do is look for a BALANCED to UN-BALANCED transformer. There’s much more to it than just a connector difference… balanced is 110-ohms and unbalanced is 75-ohms, but there is a big level difference as well.

Something like this to get it to unbalanced BNC and it should come with BNC to female RCA adapter.

https://www.bhphotovideo.com/c/product/ … hm_to.html

_____________________
Eric Seaberg • San Diego, CA • USA
A.E.S. • S.M.P.T.E. • S.P.A.R.S. • I.E.E.E.
  • Registered: 2022-10-26
  • Posts: 21

Re: XLR to RCA AES/EBU cable

I know that there are balancing adapters available from Canare or Neutrik, but it is not the case I was asking about.

4 Reply by Kubrak (edited by Kubrak 2024-01-02 11:19:23)

  • Kubrak
  • S/Mux specialist
  • Offline
  • Registered: 2023-08-03
  • Posts: 266

Re: XLR to RCA AES/EBU cable

I have checked manuals for UCX and FF 802. And UCX has suggested wireing like in UCX II manual and FF 802 has recomended wireing like that in ADI2 DAC manual.

Good to know it is not the same for all RME devices....

But why? I do not know....

5 Reply by KaiS (edited by KaiS 2024-01-02 11:25:56)

  • KaiS
  • DAW Mastermind
  • Offline
  • From: Germany
  • Registered: 2020-02-05
  • Posts: 3,126

Re: XLR to RCA AES/EBU cable

Both variants usually work:

AES to RCA, pin 1 / shield floating at the RCA side avoids ground loops, in case the connection causes ground related noise further down the signal chain.

Pin 1 connected is the safer bet, as ADI-2’s SPDIF Coax doesn’t use an isolating transformer at the Coax input.
This can cause unstable connection due to different ground potentials of the involved devices when shield is not used.


Try with Pin 1 (cable shield) connected to XLR and RCA first.
If you experience hum or other noises, cut the shield on the RCA side.

It‘s easier to cut than to re-solder the shield, so …


An additional 110 to 75 Ohm transformer is not needed in this direction.
Only from SPDIF Coax to AES such a transformer - sometimes - is needed to gain a bit more (digital data) signal level.

KaiS's Website

6 Reply by MC

  • MC
  • MC
  • Administrator
  • Offline
  • From: Germany/Thailand
  • Registered: 2007-04-06
  • Posts: 24,847

Re: XLR to RCA AES/EBU cable

The units have different digital input stages, and the manual lists the way it 'seemed' to work best. In theory the ground connection 1 to RCA GND should not be necessary...

Regards
Matthias Carstens
RME

MC's Website

7 Reply by onlyoneme (edited by onlyoneme 2024-01-02 12:24:26)

  • Registered: 2022-10-26
  • Posts: 21

Re: XLR to RCA AES/EBU cable

KaiS wrote:

AES to RCA, pin 1 / shield floating at the RCA side avoids ground loops, in case the connection causes ground related noise further down the signal chain.

Pin 1 connected is the safer bet, as ADI-2’s SPDIF Coax doesn’t use an isolating transformer at the Coax input.
This can cause unstable connection due to different ground potentials of the involved devices when shield is not used.


Try with Pin 1 (cable shield) connected to XLR and RCA first.
If you experience hum or other noises, cut the shield on the RCA side.

It‘s easier to cut than to re-solder the shield, so …

I've tried first with pin 1 floating as stated in the ADI-2 manual, and it works fine in terms of digital transmission but also increases higher frequency noise in my audio subsystem. It can be visible during measurements with Cosmos ADC. Devices to be connected this way are UCX II and ADI-2, both grounded via USB and both using standard PSUs without an earth ground.

So I've decided to ask before re-soldering as I wasn't sure if connecting pin 1 on the RCA side is fine for both devices, as manuals are confusing a bit.

I guess that galvanic isolation on the UCX II AES output is enough to prevent ground loop.

  • KaiS
  • DAW Mastermind
  • Offline
  • From: Germany
  • Registered: 2020-02-05
  • Posts: 3,126

Re: XLR to RCA AES/EBU cable

onlyoneme wrote:
KaiS wrote:

AES to RCA, pin 1 / shield floating at the RCA side avoids ground loops, in case the connection causes ground related noise further down the signal chain.

Pin 1 connected is the safer bet, as ADI-2’s SPDIF Coax doesn’t use an isolating transformer at the Coax input.
This can cause unstable connection due to different ground potentials of the involved devices when shield is not used.


Try with Pin 1 (cable shield) connected to XLR and RCA first.
If you experience hum or other noises, cut the shield on the RCA side.

It‘s easier to cut than to re-solder the shield, so …

I've tried first with pin 1 floating as stated in the ADI-2 manual, and it works fine in terms of digital transmission but also increases higher frequency noise in my audio subsystem. It can be visible during measurements with Cosmos ADC. Devices to be connected this way are UCX II and ADI-2, both grounded via USB and both using standard PSUs without an earth ground.

So I've decided to ask before re-soldering as I wasn't sure if connecting pin 1 on the RCA side is fine for both devices, as manuals are confusing a bit.

I guess that galvanic isolation on the UCX II AES output is enough to prevent ground loop.

If you‘re a solder guy - there‘s a 3rd option:

Connect shield via a resistor ca. 6.8 Ohm, paralleled with a ceramic cap ca. 100 nF.
Exact values might need some experimentation.
This decouples ground somewhat and might reduce noise.

4th option: galvanic isolation through a 110 to 75 Ohm AES to SPDIF transformer.


For listening this all won’t make a difference, but for measurements maybe yes.

KaiS's Website