Hi, and excuse the english.
I am using Fedora 29, kernel 4.20.6-200.fc29.x86_64 with Plasma KDE 5.54
CPU : Core i5 6500
MB : H170M D3H
I bought a usb headset Vykon me888, on the other system :D ... it works perfectly, so it's not a hardware problem.
On KDE, if the volume in the mixer is below...