I have what I consider a really nice set up by all accounts it should sound perfect but it seems that as I save my cash and add "better" and "better" components the noise just gets worse and worse.
I do not have a dedicated circuit... yet but I have a horrible ground or power buzz not a hum but a very loud buzz when I connect my Cable box coax to the wall.
I had the cable company out and they hooked my Manley's up to a power inverter via there truck Vol-a ground/power hum gone. The guy says I have a powered ground somewhere I checked every outlet in the house with a continuity testing plug and they all read OK.
My current set up comprises of the following Merlin VSMs Signal cable Double run Shotgun speaker wire Manley Snapper monos Powered via an MIT Z-Isolater CJ PV15 pre via a Tice Power Conditoner Purist Audio Collosus IC through out (Re-terminated by Frank at Signal Cable)
These are my problems When I switch on the Manley's I have a loud hiss from the speakers even at low volume could it be the tubes which are Electro Harmonics less than a year old.
I also have hum when I turn on the CJ this is different from the coax hum the CJ is also supposed to be filtered through the Tice power conditioner all my Power cables are ether Signal or MITs
Assuming you add a cable isolation transformer like the Jensen or the Magic Eye, most hum/buzz problems from preamp are usually resolved by relocating the pre and its ICs away from AC transformers (Tice) and AC cables.