Balanced to RCA

NEVER short pin3 to pin1 on a balanced XLR output.

@danip

It’s never a good idea to say "never" :-)

As my previous posts should make clear, I agree with your post when it comes to most designs. But there are exceptions.

You referred to balanced output stages utilizing op amps, and a notable exception to the general guideline of not shorting pin 3 to pin 1 when adapting a balanced output to an unbalanced input applies to op amp-based output stages that are "cross-coupled," which thereby provide outputs that are essentially floating with respect to circuit ground. See pages 11 and 12 of the following reference, in which such circuits are referred to as "active floating sources." And note the statement on page 13 that "Grounding one output line at the driver, which is REQUIRED [emphasis added] to guarantee stability of most "active floating" circuits, degenerates the interface to a completely unbalanced one having no ground noise rejection at all."

https://www.jhbrandt.net/wp-content/uploads/2014/11/Design_of_High-Performance_Balanced_Audio_Interfaces.pdf

That is further confirmed in the Rane document that was referenced earlier in the thread by Rauda1. See diagram 6 on page 7 of that document.

Also, while I’m not specifically familiar with the designs of the output stages of Atma-Sphere’s balanced tube-based preamps, Ralph (Atmasphere) has explicitly stated in past threads here that connecting the balanced outputs of his preamps to unbalanced inputs without grounding pin 3 will result in a huge hum. Which can be expected, given that the balanced outputs of his preamps, although not transformer coupled, are nevertheless floating with respect to circuit ground. And consequently if pin 3 is not grounded the signal on pin 2 will be received by the destination component with an uncontrolled and undefinable voltage relative to pin 1.

There are undoubtedly other such examples.

Regards,
-- Al

What needs to be known when going from an unbalanced/RCA output (such as an active electronic x/o) to a balanced/XLR power amp input (the XLR wired in accordance with AES File 48: Pin 1 ground, Pin 2 non-inverted signal, Pin 3 inverted signal)? Not in terms of impedance considerations, only in regard to the inter-connect RCA/XLR plug wiring connections.

Hi Eric (bdp24),

One way to do that is to simply insert an RCA-female to XLR-male adapter which connects XLR pins 1 and 3 together (as most such adapters do) into the XLR input connector, and use that adapter in conjunction with an RCA-to-RCA cable.

Alternatively, a cable having an RCA connector at one end and an XLR connector at the other end could be wired up correspondingly.

Another approach, which utilizes a two-conductor shielded cable, is shown as diagram 17 on page 8 of the Rane document that was linked to earlier.

Finally, a suitably chosen Jensen transformer could be used to convert the unbalanced signal to a balanced pair of signals. "Suitably chosen" would take into account impedances and other parameters.

Best,
-- Al

Great, thanks Al---Eric.

@almarg Thanks for the info never seen this kind of driver output on the devices I serviced (or did I miss that???).
I am pretty sure that everything I laid my hands was ground referenced. Transformers were a very expensive rare option (available on the better DSP or mixing consoles).

Thanks for the paper i'll give a full read when I have more time.

Anyway, If the OP wants the schematics he can just ask the ppl at DBX, I have never had a decent pro-audio/light brand refuse to hand out schematics or service manuals.