2. tech-talk
  3. 154986-2280

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
5,417 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
5,417 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.

lowrider57's avatar
lowrider57 OP
5,417 posts
 
An update and a question...
The dodgy breaker fried when resetting it to power up the Equi=Core. It left a strong burning smell in the room. Of course when the electrician was here it worked fine, but he will be replacing it.

So, I moved all components over to the other dedicated line and all is well. No hum from any toroid.
Question: is it possible to have DC offset on only one line coming from the subpanel? A heavy gauge cable from a breaker in the main service panel feeds two 20A breakers in the subpanel. Two Romex lines (same length) take separate paths up to the receptacles.

Or could there be a different issue with the one line?

erik_squires
16,237 posts
 
You could have had a bad breaker this whole time.

Yes, it is possible to have DC in only 1 leg.

It can happen if a power supply sucks juice only on the positive, but not the negative cycle, on the same phase. I could also see something funky if  your neutral was loose, but it wouldn't be DC.


Best,

E
lowrider57's avatar
lowrider57 OP
5,417 posts
 
Thanks, @erik_squires
Speaking of positive and neutral, why does a balanced power conditioner have inverted polarity? I know the 120V signal is inverted into + - 60V, but shouldn’t the polarity be corrected at the output?


More to discover