XLR, RCA and adapters: Working with active speakers and subs

I came across an interesting discussion here about XLR to RCA adapters in 2010 and I have a variant of it. My current system is an Oppo 203 to a Directstream dac, to a pair of ATC SCM19A speakers via XLR. The ATCs are XLR only. The DSD has both XLR and RCA outputs, and I'm using the former. I’m looking at adding a pair of subs, such as the JL Audio e-110s, which are RCA only on the inputs/outputs. That would mean giving up XLR, at least electrically. I ran a test with RCA’s to the ATC’s with XLR adapters, and noise wasn't a problem. I should add that by the time I do this, the Oppo and dac may be combined into a ModWright 205, which has fully balanced XLR and RCA single-ended outputs, but I don't think that would necessarily change anything in cabling.

The issue I'm looking at is how to approach cabling and adapters. If I were starting fresh, I’d run RCA’s to the subs and onto the ATC’s, using an RCA to XLR adapter for the ATCs. But I’m not starting anew, as I have two pairs of MG Audio XLR’s and would like to limit the damage in $$ and sound. How would you approach it? What do you think of using XLR’s for both runs, with an appropriate adapter on each? I’ve been warned off using external transformers or anything active, that I would easily hear any of them through the ATC’s. Thanks,
Hello Highstream,

The DirectStream DAC is described as having a transformer coupled output stage, and the ModWright 205 might also, as its description refers somewhat ambiguously to its analog stage as being transformer coupled.

Most XLR-to-RCA and RCA-to-XLR adapters short one of the two signal pins on the XLR connector (usually pin 3) to ground (XLR pin 1). Aside for some unusual exceptions (such as certain fully balanced Audio Research power amps, which require a balanced pair of signals at their inputs) that is appropriate in adapting to an XLR input, and is also appropriate in many cases when adapting to a transformer coupled XLR output. However, it can sometimes cause problems when adapting an actively driven XLR output (as opposed to one that is transformer coupled), since in those cases the active circuitry driving the signal that is shorted to ground may not be able to handle a zero ohm load.

So with respect to the connection between DAC and sub I would suggest that you contact both PS Audio and ModWright to verify that connecting the XLR output of each of those components to an RCA input via an XLR cable terminated with an XLR-to-RCA adapter which shorts pin 3 to ground is ok. I suspect the answer will be "yes" in these particular cases, but that should be confirmed with the manufacturers.

If it turns out to not be ok, though, Cardas can supply adapters on special order which leave pin 3 unconnected.

Also, I see that the input impedance of the E110 sub’s RCA inputs is 10K. I suspect both the DirectStream and the ModWright 205 will have no problem driving that impedance, but you might also ask the manufacturers to confirm that.

Regarding the connection from sub to speaker, I have been unable to find a spec on the output impedance of the sub or the input impedance of the speaker. I would suggest contacting both manufacturers to verify that impedance compatibility would not be an issue for that interconnection. But since in that case you would be adapting an RCA output to an XLR input, use of a standard adapter which grounds pin 3 shouldn’t be a problem in itself, as the experiment you’ve already performed appears to confirm.

Finally, just to be sure, I assume you are aware that the E110 provides speaker-level inputs, but that consistent with JL’s recommendation you anticipate interposing the sub and its high pass filter function between the DAC and the main speaker.

Good luck. Regards,
-- Al

Thanks! ATC said no problem with adapters. The engineer at JL Audio thought I might need to use an active adapter, but the tech I was talking to agreed with Drew Baird of Moon Audio that there shouldn't be a problem with short runs. What I mention about the ModWright in the OP was the answer to the question, "Is there anything in your builds that affects balanced and unbalanced outputs that I would need to know about in looking at how to deal with IC's and adapters?" I'll ask him about pins. Yes, I didn't state it directly, but am aware that the route will be through the subs to the ATCs.