I installed the full upgrade in January the sound was much improved but it came with a loud pop when switching on and off. I had difficulty in contacting Net Audio and have since learned that the original owner has passed away. It would seem that ownership has passed to a chap called Andy Williams. I sent the amp back to him for repair / testing to find out what the problem was. After many weeks of chasing he replied that the power boards had a problem and the amp would be fixed and returned. The amp has just been returned with the same problem. He is now not responding to emails.\nHas anybody else had a problem with this upgrade ?\nCan anybody shed light on what the problem may be .