This tutorial worked for me when I had 16.04. It also worked for me with 18.04, but I didn't do all of the steps.
What I did was to skip all of the steps, tried this in terminal that I saw in another posting.
and then went straight to step 6.
sudo apt-get install pavucontrol
With this opened, I went to the Output Devices tab and changed the Port to Line Out (unplugged). And then I saved the icon in the launcher to add to favorites. Whenever you restart or start up your system, you might need to set this setting. I wish there was an automated setting where it is always set. I also changed my configuration to analog stereo output and then moved the slider under the port setting in the Output Devices tab from Silence to 100% (0dB).
To automate it, after setting volumes through pavucontrol, from terminal:
and autorun at login the restore command (probably both by sudo, whitelisting the command on sudoers to not ask password)
Let me know if this helps.