[CentOS] Headphones volume control not working in CentOS 7

[Fred Smith]

On Sat, Jul 29, 2017 at 12:28:40AM +0200, Bernard Lheureux wrote:
> Hi all,
> 
> I hope someone could enlighten me...
> How could I resolve the fact that the volume controls of all the
> headphones I try on CentOS 7 are not working, they are OK on CentOS
> 6 but impossible to make them work on my Thinkpad Laptop with an
> iPhone headphones or a Marshal Monitor plugged with a jack
> connector...
> Those 2 headphones work correctly in CentOS 6...
> What could I do to get the same behavior on CentOS 7 and this damned
> Gnome 3 ?
> Thanks for your help...

On Centos-7, some apps use PulseAudioVolumeControl (pavucontrol)
instead of the one that defaults to the top panel. (I am running
Mate, not Gnome--yuck--so YMMV).

I wish there was a way to control all from a single place, but AFAICF
there isn't. for some things I use the one on the top panel (which is
Mate Volume Control) and for others I gotta start up pavucontrol.
it's a nuisance.

My USB phones seem to be controlled by the pavu control, while the
speakers tend to be controlled by the mate volume control. and I can't
get my old analog (1/8 inch plug) headphones to work at all anymore,
no matter what control I use or how I poke at it, all the sound comes
from the speakers (which are plugged into the line out [green} jack
on the rear of the computer, while the headphones are plugged into the
green jack on the front.)

digressing a little... A few years ago my systems all supported 
auto-switching between speakers and headphones when the phone plug
was inserted, but the only one I have now that does that is my netbook.
the current desk-side system and its last couple of predecessors now
do not do that. Go figure.

-- 
---- Fred Smith -- fredex at fcshome.stoneham.ma.us -----------------------------
                       I can do all things through Christ 
                              who strengthens me.
------------------------------ Philippians 4:13 -------------------------------