Balanced to RCA

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.

NEVER short pin3 to pin1 on a balanced XLR output.

@danip   If the equipment supports the balanced line standard then this should be no worries at all. But it is worthy to note that most high end audio equipment and a fair amount of studio gear doesn't support the standard.

The standard (AES48) calls for the outputs of an XLR (IOW, male XLR) to not reference ground. There really aren't many ways to do that! An output transformer is one way, and obviously if one side of the output secondary is tied to ground (pin 1) its no worries whatsoever. Our preamps are another way this can be done as they have a direct-coupled (tube) output (for which we obtained a patent) that supports the standard, so they too can have one side tied to ground with no worries.


If an output is at risk of damage, this is because its being shorted out, which means it is referencing ground and so does not support the standard. When the circuit references ground, it defeats one of the purposes of using balanced lines, which is to prevent ground loop hum and noise. This practice also allows the interconnect cable to impose an artifact on the the sound, as the shield is being used as a signal circuit return, allowing noise to intermodulate with the signal. Now many studio products that don't support the standard try to get around this problem by having a low output impedance, which swamps the noise, but it should be noted that **any** device that has an XLR output should also have a low output impedance.