I always wondered if it was just me or other people noticed the change is sound quality too. I knew I wasn't imagining it, but always wondered if the situation was common. Anyway, I use two of the Blue Circle Noise Hounds now, and have found much more consistent sound quality in my system. I had tried some power cords, which made some sonic differences, but did not make the sound any more consistent. Whereas the Noise Hounds made the system sound as good during the day as it does late at night. Thus, the hypothesis of noisy lines certainly seems believable to me.
Different & inconsistent sound quality
I am noticing different sound quality from my audio system, depending on when I listen to them. My system consists of Krell integrated amp, B&W CDM 1SE, and Sony DVP-7700. They are connected with Transparent ML Super interconnect and MIT T2 Biwire speaker cable. For example, in the moring and very late night, piano recordings sound very clean, detailed, and transparent, however, in late afternoon or evening, it seems that some of piano notes from the same CD sound very dull and veiled. The phenomenon is true of other recordings of cello, violin, and etc. I suspect that AC noise has to do with the problem, so as a first step, I consider upgrading stock power cord for my integrated amp to a better one such as Transparent PowerLink Super or others. Could anyone help me with any possible solutions to the problem I'm experiencing? Any suggestions or comments would be greatly appreciated.