Hi @Remus1971, welcome to the community.
Those symptoms sound like the Amp is clamping its volume down to protect it from faulting. There are a few reasons why it might do this such as overheating, detecting a short in the speaker wire, or more likely in your case, trying to push too much power to speakers that can’t quite handle it. It clamps like this to protect itself as well as the speakers that are attached to it. I recommend getting in touch with our customer care team to figure out why your ZP120 is behaving in this way.
Mark good posts by pressing the like button, and select the best answer on questions you've asked to help others find solutions.