Equi=Core Hum & Other Issues

Lowrider57 said:

This leads me to the question; can DC offset be measured by the electrician either at the service panel or the wall receptacles?

DC on the AC mains can be measured at either location. In your instance you want to measure it at the wall receptacle outlet that you are using for your audio equipment.
Question is does the electrician and or electrical contractor you have hired have the test equipment to properly measure for DC voltage on the 120Vac mains. Unless the electrical contractor/electrician has a power quality analyzer meter something like this one then the answer no.
https://www.fluke.com/en-us/product/electrical-testing/power-quality/437-series-ii#

A typical good quality digital multimeter (DMM) will not correctly measure for DC on the AC mains unless a low pass filter (lps) is used. The lps is connected between the 120Vac mains and the DMM. The DMM is set to auto DC Mv.
I have a FLUKE 87 DMM and it cannot correctly measure for DC on the AC mains. I made a simple lps. Nothing to it. It’s of a lot cheaper than buying a power quality analyzer meter.

I don’t know how big the electrical contractor/electrician is that you have hired.
I do know a few good sized electrical contractors in my area. They could easily afford to buy a $10,000 power quality analyzer meter. I doubt if any one of them has one setting on a self in the shop just setting there waiting for the next time it will be needed.

If they have a customer where they may have a power quality problem in their facility the electrical contractor hires a Power Quality Testing Company. For around $150 to $200 an hour you can hire a Power Quality Testing Company that employs qualified, certified, trained, technicians to preform the power quality testing. The testing company furnishes the electrical contractor a complete certified test report when they are finished.

Do you need to hire a Power Quality Testing Company? Probably not.
I do find it odd though that the transformer in the Atma-sphere power amp is mechanically vibrating more than it normally should. It’s my understanding Ralph installs a DC blocker in all his amps that use a Toroid power transformer.

Quick test. Check/measure the AC line voltage at the duplex receptacle wall outlet with the power amp turned on. You want a conned load for the test.... A higher than normal AC voltage can cause a power transformer to buzz, mechanically vibrate, louder than normal. Normal? Voltage should be around 120V.123Vac is getting on the high side. 124Vac -125Vac and higher is definitely on the high side.... Look on the rear panel on the amp, what is the recommend nominal AC line voltage for the amp?

Jim

Correction:
Low Pass Filter (LPF).
NOT lps.

.

There are many DC blockers available, at different price points.  PS Audio used to make a popular one, occasionally available used.  Audio by Van Alstine, Emotiva, and Isotek all have models.

@jea48 , this is a large electrical contractor in Philadelphia. I’ve been with them since they were a small family business. Now their prices are high and using younger techs. My guy, a master electrician who knew audio and owned a nice system is no longer with the company.
He did test for DC offset and polarity when he upgraded my power 3 years ago.

This morning line voltage was 124VAC on my monitor I keep in one of the duplexes. That’s high, it’s been steady at 122V for years (using a Furman conditioner with voltage display).
I’ll test voltage on the amp line as you suggested. I know Ralph uses a DC blocker in his amps.
Many thanks, Jim.

@jea48   Multimeter reading on the dedicated Atma-sphere line is 123.0V. Amp is powered up with no transformer hum. I guess I should take a reading when the amp is humming.
 
BTW, the digital line measured 123.8V and later dropped to 121V, so voltage is fluctuating.