The Unity/gtk volume manager that comes with vanilla Ubuntu lets you increase the volume past 100%, which is useful for hearing quiet youtube videos. Is there a way to achieve the same thing with the KDE mixer app?
Left click on the KMix plasmoid then on "Configure Channels" button:
In the "General" section of the widget settings check "Volume Overdrive" checkbox.
im not to familair with KDE but, you could try using the alsamixer program in the terminal
The best solution for this (in my case, as all the volumes in
alsamixer were to the maximum) was using Veromix.
First install python script engine,
sudo apt-get install plasma-scriptengine-python. Then right click your destop and select the option add widgets. Select the option "Get new Windgets" and "Download new plasma widgets", then in the search box type in "Veromix".
Once you have it, add it to your desktop or to a panel, and go to veromix settings, select PulseAudio tab and select the higher volume range that you want (up to 255% is allowed, it is not recommended going higher than 200 as that may damage the speakers). Hit Apply and Ok.
You may need to toogle a bit for the changes to take effect. For example, in my case, after I set the volume to 255, I went to the widget and selected an arrow pointing left, right next to the volume bar. Selected unlock channels, and repeated the process (I locked the channels again), that way the volume bar allowed me to set the volume to 255%.