i would still use a good power conditioner. even with a dedicated line whether it be romex or say another type of wire. you are still going to get noise coming in. this makes a good power conditioner a must so as to filter out any noise that is going to get in. you are also going to pick up noise from your other components. another reason to get a power conditioner is for surge protection( lighting, power spikes etc). romex is going to be ok but a wire that is made for audio dedicated circuits is going to be better( more dynamic, smoother, a bit more on the quiet side).
as far as your phono stage is concerned it sounds like you have isolated the problem. power supply or bad tubes sound like the culprit. i take it that your phono stage in made in china( most are now ). send it back and get a new one or see if you can get one that is made in the US. i am not a fan of chinwa audio gear.
hope this all helps. good luck and tell us how you make out.
R.
I would get a good power conditioner if it didn't cost as much as my beloved rm10.
Allnic is a well respected S. Korean audio shop.
In fact, I have (for other reasons) swapped out my original stage for another one, and it results in the same problem. Perhaps the stage's ground wiring is done incorrectly? I was also thinking that it's not the Allnic per se but rather its interaction with my passive pre. Is that possible? I don't have another pre to test this.
At any rate, if Roger ever releases his phonostage, I'll be in line. I'm certain it'll be much quieter than what I have.