Can an unbalanced-to-balanced adaptor damage an amplifier?

Yeah, my dealer has had a question in to T+A but no reply so far from Germany.

The issue, I’m finding out, is that XLR connectors can have two different pin outs. If an adaptor, or a cable with a balanced connector, is wired to the wrong standard, then it would short the output of most home-audio amplifiers.

Some amps can survive a direct short for at least a few seconds. And the majority of audio-targeted adaptors are wired correctly these days. But when you buy an adaptor online, you may not have any idea if it’s designed for home audio, pro audio or some other application, how old it is, etc, nor how robust your amplifier is in the face of a direct short.

Depending on what T+A tells me, I guess, I’ll consider buying the company’s own TRS-to-Pentaconn adaptor for $200. But it would be nice if I could get away with something cheaper.

Anyway, this took a bit of digging, since it’s obviously not an issue on many people’s radar. But I think what I outlined above is accurate.

The issue for any amplifier, headphone or speaker, is whether the (-) side is active or grounded.

99% of all amplifiers out there only drive the (+) terminal and leave the (-) attached to the signal ground.  Sometimes those amps can be bridged so that you use the (+) of channel A for the red and the (+) of channel B as the black wire.

In the case of grounded negative terminals, there’s no difference between the two speaker (-) terminals and they can be safely jumpered together. The (+) terminal however cannot be jumpered together. Even small differences in voltage can cause massive current flows.

The problem is when the (-), like the (+) side is driven, and the same problem applies. Even a small (0.5V) voltage difference can cause very large current flows to occur. A simple 4 conductor to 3 conductor adapter likely shorts the two (-) together which would be bad.

Thanks, Erik. That’s good input -- although your last paragraph, I think, highlights the problem: Unless a manufacturer publishes a pinout, buying an adaptor can be a crap shoot until you have it in hand & can check it out with a multimeter.

*******UPDATE

Just got a reply from T+A.  Guess this answers the question:

"The balanced Pentaconn headphone output transmits the audio grounds of the right and left channels separately. This is also the principle of balanced transmission. The two audio grounds can easily be bridged using an adapter (e.g. from Pentaconn to unbalanced 6.3 mm stereo jack plug). This will not cause any damage to the R2500R! For this case (Pentaconn to 6.3mm jack plug) we also have an adapter with the article number 4683-99101 in our accessories program."

FINAL RESOLUTION

I plugged in the headphones with the Amazon adaptor & they work fine. The T+A hasn’t been reviewed yet, but I can confirm that it drives my 22-ohm Audeze phones quite nicely. Can’t comment on SQ b/c nothing is broken in yet, but even now, I don’t hear any red flags, not even in the bass.

If the sonics ultimately are not clearly superior to my Class-A Audeze HP amp, I may spring for the T+A adaptor, which seems to be much better made. But for now, I’ll sit tight.

Thanks everybody for your contributions to this discussion.