Dedicated Line Noise Filter?

Many thanks, @whart . I agree that @jea48 has the knowledge that crosses that boundary between electrician and electronics. All that and I bet he can cook. 

Thanks Bill (whart), and lowrider57, for the kind words.

Jim

Question for @jea48 or @almarg ...

The sub panel feeder Hot/s, neutral, and safety equipment ground conductor are all fed from the same main panel.

The sub panel feeder neutral conductor/neutral bar can not be bonded, connected to the sub panel metal enclosure or the equipment ground bar. The feeder neutral bar must be left isolated/insulated from the metal sub panel enclosure. (Green bonding screw or neutral bonding strap that came with the panel discarded.)
If the the feeder neutral conductor/neutral bar is bonded to the enclosure/equipment grounding conductor/equipment ground bar then the equipment grounding conductor will be connected in parallel with the feeder neutral conductor. What happens then is the equipment grounding conductor will carry neutral current back to the main electrical panel, or where the service neutral is bonded, connected to the enclose, equipment ground, and earth.
Not good for the equipment grounding conductor to carry neutral current.

If the subpanel (containing breakers for 2 lines) takes a feed of hot, neutral, and safety ground from the main panel, are these 2 new lines truly dedicated?
  IOW, by tying in to the main panel (which may have shared neutrals and grounds), is there a chance of causing a ground-loop in the new lines originating from the subpanel?

lowrider57

If the subpanel (containing breakers for 2 lines) takes a feed of hot, neutral, and safety ground from the main panel, are these 2 new lines truly dedicated?
  IOW, by tying in to the main panel (which may have shared neutrals and grounds), is there a chance of causing a ground-loop in the new lines originating from the subpanel?

Yes, that is how a subpanel should be wired. Provided that the lines go directly from the subpanel to the receptacle used by the components, those are considered dedicated lines.

Tying the neutral and grounds together at the main panel is required by code and helps prevent ground loops.

@lowrider57 - @cleeds has it right- all "dedicated" means for our purposes is that the circuit isn’t being shared by other appliances, switches, lighting, etc. It reduces, but does not in my experience, eliminate, noise from other parts of the electrical system. My set up in NY (which was "permitted," but didn’t follow best practices I later learned), picked up noise from a low voltage light two floors away, and from various plug-in appliances, like a humidifier or hair dryer being used in another part of a large house. I also suffered from a nasty zap over the lines every time my tonearm  air compressor motor kicked in- this could have been eliminated by properly separating the lines rather than bundling them.

I guess the other reason why one would install a dedicated line is to be sure that you have no competition for current drawn from the same line.
I believe that the job done in TX in my new place is far better than the one in NY, based in part on the level of knowledge of the electricians, and my prodding with questions (some of which were helpfully answered by @jea48 along the way).