Each time I log in I need to make PCM move to 100 value because sound is too low. I have option Startup → Restore volumes on desktop startup active (marked). I want to set it in some configuration file so that it doesn't change. I want to change volume only with Master because I use keyboard shortcut for it. This would be the most convenient way to manage it. I had to remove PulseAudio.

Hm, unless you use a very, very old distribution where Pulseaudio is not integrated, this is a bad idea. Please specify your distribution and Plasma version

It is Plasma 5.8.9 on Kubuntu 16.04. Unfortunately I need to use it because of another application that I have to use in the specific version that is on 16.04.

PulseAudio was very buggy on this release so I had to uninstall it.
I repeatedly got the error message:
https://i.imgur.com/lmpiQIK.png

It is not a big problem. I can live with it but I imagined it will be as easy as to edit some configuration file to set PCM fixed value.

how about updating your distribution? The current release is 18.04, and you would get also a newer plasma. Removing an essential component of the sound stack is really not a good idea...