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TRRS v TRS: what are they on about?

adc

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Yeah, I know how they differ, and I can easily see how misconnections could occur depending on the tolerances of the jack. If physical connections were bridged, reversed, or shorted, I could imagine the effects being audible: hum, phasing issues, unstable connections, etc. However, I've occasionally used TRRS plugs (on, say, Apple earbuds) in TRS jacks for years, and have never experienced any dramatic, or even detectable, undesirable side effects. Just plain old stereo audio.

Yet, the third -- not the first, nor the second, over several years -- Schiit headphone amp that I recently acquired, in this case a recent Magni Heresy, came with a big ol' warning insert about the incompatibility of TRRS plugs with TRS jacks, and a link to an adaptor that they'd be happy to sell me. Now, of course, one could argue that they just want to sell adaptors, but it's five bucks, so I doubt it's a lucrative line for them; thus I'm guessing their pitch is rooted in a legitimate concern.

So ... what are the "problems" that remain undefined by this dire warning insert? Am I simply deaf to the implications, and thus have never noticed the horror I'm inflicting upon my ears by doing so? Are the potential problems with this combination rare enough that I've simply never encountered them? Is there something different about the later-production Heresy which makes it more susceptible to misbehavior when subjected to a TRRS-equipped peripheral than was the original, late 2019 Heresy?

I must know.
 

somebodyelse

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Your best bet is to ask them, otherwise it's just speculation. I don't remember the names of the Schitt guys who post here, or I'd address it to them. My guess would be some manufacturer(s) using the 17mm TRRS variant instead of the usual 15mm, and people have caused damage trying to force them all the way into the amp socket, but it could be a corner case with the mic and control electronics in some headsets.
 

mansr

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incompatibility of TRRS plugs with TRS jacks
There are two different pin assignments widely used with TRRS connectors:
  • Left (T), Right (R), GND (R), Mic (S)
  • Left (T), Right (R), Mic (R), GND (S)
A TRS plug will always work in a TRRS jack since the sleeve simply shorts the mic input to ground. With most TRS jacks, the sleeve of a TRRS plug will not make contact at all while the outermost ring connects to what the jack calls the sleeve. That means a headset wired according to the first option above will work whereas one with the other wiring will not.

If they are concerned about compatibility with TRRS plugs, they could have fitted a TRRS jack and wired the outer ring and sleeve together. That would work with any plug regardless of its wiring.
 
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AnalogSteph

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There are at two different pin assignments widely used with TRRS connectors:
Plus the altogether different 2.5 mm TRRS mono headset pinout found on older phones (e.g. Nokia), plus balanced headphone amp outputs using TRRS jacks, usually 2.5 mm as well.

I suppose the note may be related to headphones intended for the latter, which would be incompatible indeed.
 
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