I never get time to listen to HP anymore and so sold my unit. During transit, some of the side screws came a little loose and the front faceplate/fascia was thus loose. This pushed outward causing the volume knob to have a scratchy-stuck feeling, which the new owner was dissatisfied and wanted to return it. I was flabbergasted, and the unit was sent back to me. That is not the way the world works here, but I accepted the return and found the problem.
So, if anyone is having a scratchy and stuck vol knob then just push the front fascia while tightening the side screws and it's all fixed.
Had a short listen, and the sound was just great! Looks like I will keep this little gem for the rest of my life!
Really good HP amp, but sadly lots of people look to buy something else these days.