Hello,
whenever I run
sound goes mute in alsamixer on Master M channel. Why?!
I used
but still when I run mplayer in different TTY (I'm not using any X) then I always have to unmute master channel in alsamixer.

Please advice!

The original folks who wrote alsa apparently imagined us all with big woofers on hundreds of watts amplification. So in case we'd blow speakers with the power-on "Whooompf!" as we charged our 1 Farad of capacitors, muting the output seemed smart to them… very strange and weird as it seems.

It turns out alsa users are in the main are using small speakers usually amplified only by the soundcard and we have microphones in the vicinity. So we don't want huge volume and get annoyed when alsa mutes the sound again. I have found little cure but to be aware of it.

It's wierd. I'd like to set the output level ~40% and save it somehow, yet mplayer keeps muting all

Since mplayer does it why not have a closer look at its configuration files? I don't have it any more as I switched to mpv long time ago, can't give more detailed help. Running alsactl is clearly missing the target, it sets the levels for reboot, it won't automatically correct levels every time user adjusts levels, because this is what you are doing with mplayer. As a matter if it did then you would go mad, every time you adjust sound levels it would reset them, clearly undesirable.

I'd also question your alsactl syntax. 'alsactl store' stores the current values, which is hardly what you want if the sound is muted.

Fix the sound, then run 'alsactl store' once. When mplayer mutes the sound, get into a terminal and run'alsactl restore' which overwrites current values with the saved ones. All alsactl commands need root, so use sudo as needed.