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Help I think my AC is polluted

After months of trouble shooting, I've come to the conclusion that my AC is the culprit of a very annoying hum. The thing that's odd is it only occurs every couple weeks, and only for two or three days at a time. The other thing that's strange is it happens on the weekend and ends usually by Monday night.

Let me give a few details about my system.
- I recently installed two dedicated 20 amp lines. This did not change the intermittent hum.
- I've tried cheater plugs during the hum and they had no effect.
- I'm in the process of auditioning two power conditioners. The Equi=tech Son of Q Jr. and the Furutech e-PT609. Niether of them has had any effect on the hum when it's happening.

I've put my ear right next to each component during the hum and found the Equi=tech transformer humming. I turned off all other components and the Equi=tech continued to hum, even in standby. When the hum is gone, the Equi=tech is dead quite. The hum doesn't change whether the powercords are plugged into the wall or either power conditioner.

I'm going to give the power company a call but I don't expect much help from them. I may try putting in an isolated ground and see if that helps. According to Equi=tech, balanced power should take care of most all ground loop issues, so I don't think an isolated ground will help much with this problem.

Has anyone else ever experienced this? Any ideas on a solution?

mootsdude

Showing 3 responses by jea48

jea48
4,672 posts
 

Mootsdude posts;

The thing that's odd is it only occurs every couple weeks, and only for two or three days at a time. The other thing that's strange is it happens on the weekend and ends usually by Monday night.
>>>>>>>

Is your house fed by a utility pole transformer?
If so go outside and see if you can count the number of houses that are fed from it. Sometimes 4 to 6 houses
Next thing to check is your neighbors that are connected to the same transformer. Any weekend body or machine shops. Any Arc Welding on weekends?

Next time it happens check the voltage at the power Amplifier's receptacle outlet with the Amp on and a source playing.

Take a walk outside and listen for any abnormal noises coming from any neighbors garage.
=======

I've put my ear right next to each component during the hum and found the Equi=tech transformer humming. I turned off all other components and the Equi=tech continued to hum, even in standby. When the hum is gone, the Equi=tech is dead quite.

Read the specs on the Equi=tech, bet it has a toroidal iso transformer in it. This louder hum than normal is caused by DC offset voltages on the utility AC line. Do a search on Google for more information, what causes a toroidal transformer to hum loudly.
I recently installed an iso xfmr for my Arcam Alpha 9 CDP. The Arcam has a toroidal power xfmr and at times the toroidal transformer was mechanically noisey. Connected to the iso it is quiet.

You also mentioned in your post that the lights in your home would get bright and dim. Brighter than normal? Do light bulbs burn out quicker than normal?
Jim
jea48
4,672 posts
 
http://www.diyaudio.com/forums/showthread/t-2080.html
jea48
4,672 posts
 
Jmho excessive mechanical noise of a toroidal transformer is not due to low voltage. It is due to DC offset voltage on the AC power mains.

Here is a link for the industry standards for power companies. The nominal AC power voltage they should maintain to the customer shoud be within plus or minus 5%. Usually a + or - 10% range for equipment.
http://powerstandards.com/tutorials%5CVoltageRegulation.htm
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