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Equi=Core Hum & Other Issues

I’ve owned a Core Power Tech Equi=Core 1800 for 6 months. Recently the transformer has started to hum inside the chassis. It happens when components are on and also when sources are powered down. The transformer hum is intermittent. It ranges from multiple times per day to 3 or 4 days without any hum. I never had DC on my dedicated lines before, so I picked up a Klein Tools AC/DC tester... https://www.kleintools.com/catalog/electrical-testers/electronic-acdc-voltage-tester-12-240v-ac-15-2...
and when plugged into wall receptacles it indicated overload. Line voltage is steady at 122VAC and always has been.
What am I doing wrong, and how should I test for DC on the power line?

I discovered another problem when testing the Equi=Core duplex receptacles; they indicate inverted polarity. All house outlets measure correct polarity.
I’m looking for some assistance in diagnosing this hum. I’m not sure if it’s due to DC offset or if the torroid itself is vibrating in its mounting.

I know this is becoming a long thread, but I must mention that the Equi=Core now trips the breaker at the panel when powered on. It trips several times in a row, eventually allowing power-up. This is a 20A dedicated line from a subpanel which I’ve had for years.
Any advice is much appreciated.


128x128lowrider57
lowrider57's avatar
lowrider57 OP
5,397 posts
 
@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.



lowrider57's avatar
lowrider57 OP
5,397 posts
 
@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.

tuffy72561
181 posts
 
l@owrider57

   Next time it hums I would walk around your place and look for anything turned on that may not always or usually be on. Once I figured out the curling iron thing I never had a problem again. Who would have guessed. Good luck.
lowrider57's avatar
lowrider57 OP
5,397 posts
 
@twoleftears  Thanks.
I'm aware of the Van Alstine as an inexpensive solution...
https://avahifi.com/products/humdinger-dc-line-blocker

The Isotek looks great with its ability to rebalance the AC sine wave, but it's expensive.
https://www.musicdirect.com/power/IsoTek-EVO3-Syncro-Uni-Sine-Wave-Rebalancing-Unit-C19?variant=AISO...

I used to own the Emotiva when I was having ground faults. I guess about five years ago, and there was never any DC on the mains.
As I stated earlier, this issue is a recent occurrence, but a very real problem.


lowrider57's avatar
lowrider57 OP
5,397 posts
 
Tuffy, while the Equi=Core was humming I turned off the refrigerator and other appliances. And no dimmers in my house. I live alone so I know what devices are being used. Although I forgot to turn off the router.

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