@screener, thanks for your reply and sorry for my late reaction. I tried all sorts of things but wanted to do that again to have a clear start to find what is causing it but haven't had the time yet.
But a while ago I tried different cord, different outlet, different pre-amp with only one (different from regular set) inputsource, different speakers (passive) and different XLR and RCA cords; the hum stayed. The NuPrime's are normally hooked up to a pair of Martin Logan ESL11A, when I hook those Impressions up to my Advance Acoustic X-A220 mono's there is no hum on the speakers.