Re: 3.5mm jacks (was Re: [gentoo-user] Bluetooth speakers)

[Michael]

On Tuesday, 10 May 2022 11:29:51 BST karl@××××××××.se wrote:
> Michael:
> ...
>
> > Jacks have a TS, or TRS, TRRS, or TRRRS contacts arrangement, depending on
> > the connectivity they are meant to offer - mono, stereo, stereo+mic and
> > whether this is balanced or unbalanced.
>
> ...
>
> I have an old laptop (Thinkpad T61p [1]) with a stereo and
> microphone jack, both 3.5mm.
>
> How do one know if it is a TRS or TRRS variant without opening the
> case ?
>
> Maybe it is a trrs jack since when I inserts a trs cable (to speaker)
> the ouput sound whines a lot, mostly masking the intended sound.
>
> I found some specs in [2] and [3].
>
> Regards,
> /Karl Hammar
>
> [1] https://www.thinkwiki.org/wiki/Category:T61p
> [2] https://www.headphonesty.com/2019/04/headphone-jacks-plugs-explained/
> [3] https://en.wikipedia.org/wiki/Phone_connector_(audio)

I'm not familiar with the specifics of your laptop.  It is a matter of digging 
through spec sheets to find out, or opening up the case, but often the socket 
is enclosed in a plastic molding.  Checking part numbers may reveal what the 
contacts arrangement is.

If you're only getting one channel audio or noise/distortion, after the jack 
has been inserted fully, then it is likely you have a mismatch between the 
jack & socket contacts.  In all likelihood you have a TRRS line-out for stereo 
earphones and perhaps a TRS line-in for mic mono.

Sadly there is a historical mismatch between different manufacturers' pin 
arrangements, especially so with camcorders and old portable DVD players 
(remember those?!)  So there's no guarantee some mic or earphones released by 
one manufacturer will always work with other devices.  The contacts look the 
same, but the ground and live connections could be reversed.  With PCs the 
contacts tend to be more standardised.