When I had Windows 7 on my machine (Lenovo W53) the sound volume was high enough that I usually set it at ~50%. With Jessie 100% volume seemed barely adequate, and I was experimenting to see if I could get more. In KDE->System Settings->Multimedia I played with the settings; the result was that no available playback devices are shown. Pressing the "Reset" and "Defaults" buttons at the bottom of the screen had no effect. How can I get back to the defaults?