i have the same problem. It´s hard to control the volume with the master volume. When i turn the volume 1 mm then its going up to the full volume and my ears nearly explode. I play my valve in my arpartment and so its hard to control the volume. I do at the moment a workaround that I use the "Channel Volume" but everytime i switch to another sound, the volume is going to maximum. The master volume is currently not to control with the knob.
Do you have an idea, what i can do with this knob ? Can i use any spray. Is is hard to pull the know out, that i can use contact spray ?