Dedicated Line Noise Filter?

@lowrider57,

On second thought, if you see the green bonding screw on the neutral bar or a bonding strap connected to the neutral bar that is connected to the metal enclosure, do not remove it.

Post back what you find. Do not change anything in the panel.

Just post back what you see.

@jea48 , Thank you so much for taking the time to share what I consider expert advise and knowledge.
I'm going to email your information to the electrician and we'll find out what is really going on. (I'm hoping that I'm wrong about how the subpanel is wired).
And @almarg , you're always a key resource for any audio issues I have.
 
What do you fellas think is the issue with the Atma-Sphere preamp (single ended)? It has always caused hum in my system.
It is designed with star-grounding and I confirmed that the safety ground is tied to the chassis. (also confirmed the grounding on the amp). This hum (which sounds like a ground-loop) has been constant even during the time I had the original dedicated line. Before that, I had a Rogue pre with no issues.
Your thoughts?

did you get construction permits for this project? Was the work inspected by your town's electrical inspector?

@cleeds , I just noticed your post. In Philadelphia, a permit is not required for an electrical addition or upgrade in a residence.
The law states that an inspection is required at the time a house is being sold.

Thanks for the nice words, Lowrider.

Given that when only the preamp and power amp are connected there is a loud hum when a cheater plug is not used and a lower but still significant hum when a cheater plug is used, it sounds like two problems are present. One being a ground loop between preamp and power amp, and the other probably being due to something internal to the preamp, such as some of the possibilities Davehrab mentioned.

I say "probably" because it is also conceivable that what you are hearing when only the preamp and power amp are connected is the result of having the preamp’s high impedance inputs left unconnected and essentially "floating." Unconnected high impedance inputs often tend to be susceptible to pickup of hum and noise, that may even be coupled into them from elsewhere within the same component. Which would have no relevance to what would occur when a powered up source component having reasonably low output impedance is connected. And if you also hear a low level hum when a powered up source component is connected, perhaps that is due to a ground loop between source component and preamp. (Although if I recall correctly you may have sorted out that possibility some time ago with a Jensen transformer and/or a cheater plug).

But to assure that assessments that are performed with unconnected inputs are meaningful it would be desirable to purchase some RCA shorting plugs. A search for "RCA shorting plugs" at eBay will return many sellers offering those at low prices.

Finally, regarding the possibility of an internal problem in the preamp, the next time you are in contact with Ralph (I recall that you’ve discussed this issue with him) you might ask if the UV-1 uses AC or DC on its tube filaments. While I suspect the answer will be DC, if perchance AC is being used I would speculate that a tube problem may be contributing, unless you've eliminated that possibility via tube substitutions.

Good luck. Best regards,
-- Al

@almarg ... Thanks, Al. Can always count on you. I thought about using shorting plugs a while back, but now I can't remember if they can be used on the UV-1. I'll reach out to Ralph next.

What if Lowrider57 has lost a power supply cap or has a cracked solder joint in one of his component's

Yes, it's possible that there is an internal problem.
I did use a Jensen, following your recommendation, on the preamp output and the sonics were so terrible I quickly removed it. Ralph has stated many times how adding a transformer inline with an OTL component can have a negative effect, and wow, he was not kidding. So I can't remember if it corrected the ground loop.

The Jensen did perform well on the source which was involved in the ground-loop in my system. If you recall, my Sunfire amp was designed with the signal and the safety ground tied together, which threw a wrench into the entire system. I now have a tube amp, properly grounded, so there should be no ground-loop. I can't confirm that, of course, until the electrician verifies that his wiring is correct.
Many thanks to you and Jea48,
Jim