Balanced to RCA

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

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

@sunnybaker

As Bob and Mike indicated earlier the best approach to connecting a balanced output to an unbalanced input is widely considered to be with a Jensen Iso-Max transformer.

A suitable transformer, given that you are using a two-channel amplifier (as opposed to monoblocks) would be the Jensen model PI2-XR. It is available here for about $270 in a configuration having XLR inputs and RCA outputs. (That page shows a PI2-XX, having XLR connectors for both inputs and outputs, but you can specify RCA output connectors in the options menu near the bottom of the page). Further details can be found at the Jensen site.

A transformer such as that would eliminate the possibility of ground loop issues, and it would provide essentially the same noise rejection as a balanced interface would provide. Or perhaps even better noise rejection, because its bandwidth limitation of about 55 kHz at -3db will tend to filter out RFI that may be present. It would also eliminate whatever audible significance the "micro-capacitive flutter" effect that Teo referred to may have. (Although I would not expect that effect to be significant if an XLR-female to RCA-female adapter leaving pin 3 open is placed at the output connector of the dbx unit, and is used in conjunction with an RCA-to-RCA cable. I suppose it might be significant if an XLR cable is used in conjunction with an XLR-to-RCA adapter at the input of the destination component, due to capacitive coupling that may occur within the cable. And there certainly may be an issue if pin 3 is left open on an XLR **input**; when adapting an RCA output to an XLR input pin 3 should be grounded).

Regarding the need for additional cables with a Jensen transformer, as you can see in the manual for the PI2-XR the cables on its output side must be very short (no more than 3 feet long, and preferably less, depending on the capacitance of the particular cable). So given the minimal length they shouldn’t cost a great deal, and whatever sonic effects they may introduce should be less than if they were longer.

Regarding the use of adapters or adapter cables at the outputs of your dbx unit, to expand on my previous comment a bit the only situation in which it is necessary to ground pin 3 when adapting an XLR output to an RCA input is when the signals on pins 2 and 3 are "floating" relative to circuit ground (i.e., the voltages between those signals and circuit ground are not controlled or defined, or putting it another way the signals are essentially "isolated" from circuit ground). That is not the case in most designs, and I suspect it is not the case with your dbx. So I think it likely that connecting pin 3 to pin 1, either directly or via the 10 ohm resistor you referred to, won’t do any good and conceivably could do harm, eventually if not sooner. But without a schematic or other detailed knowledge of the specific design I can’t say that for sure.

Regards,
-- Al

@david_ten

Thanks for the mention, David. Most (but not all) XLR-to-RCA adapters ground the signal on XLR pin 3, i.e., they connect pin 3 to pin 1, which is the ground pin. In the case of most (but not all) components providing XLR outputs that kind of adapter should not be used, for the reason @mike_in_nc stated. And the same considerations apply in the case of an XLR-to-RCA cable.

Following is an excerpt from what I had said when we discussed this issue via PM in November 2018:

An adapter that shorts pin 3 to pin 1 would be appropriate when adapting an RCA output to an XLR input, and would be appropriate and sometimes even necessary with **some** designs (especially some tube-based designs having transformer coupled outputs) when adapting an XLR output to an RCA input. However in many cases, especially cases involving solid state designs having low output impedances, such a short could cause adverse sonic effects, buzzing, or even damage, eventually if not sooner. I once diagnosed a severe buzzing problem that occurred with a member’s CD player which was caused in exactly that manner. When he went to an adapter cable which left pin 3 open everything worked fine.

You subsequently received a response from the designer of your Grandinote preamp stating that pin 3 should be left open (unconnected) when adapting its output to an RCA input.

And chances are that would also apply to the OP’s situation, but not necessarily. For a firm conclusion to be reached he should either ask the manufacturer of the component providing the balanced output (as I see Mike suggested just above), or let us know the specific make and model of the component and we may be able to determine the answer.

Best regards,
-- Al