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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
jea48
4,451 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
gs5556
1,235 posts
 
"Dirty AC" will not cause transformers to hum, but direct current in the AC line will (transformers are AC devices). It sounds like you're getting excessive DC in your house on those days. You can complain to the power company or you can buy DC blockers like the ones sold by PS Audio, Xantech, etc.
tobias
1,534 posts
 
Fascinating to hear that undervoltage can lead to hum. That conforms to my experience: our AC line hums most in winter, when heating is on and power draw would be highest.

Humming toroids eh? My loudest hummer is a Chinese integrated with an 800VA toroid in it.
jea48
4,451 posts
 
http://www.diyaudio.com/forums/showthread/t-2080.html
jgreene
18 posts
 

My BAT amp's 1000 KVA toroid transformer hums loudly when my girlfriend uses her hair dryer. Scared the heck out of me when it first happened; I thought that something had gone bad in the amp. But it was low-voltage. I just turn the amp off now before she turns the dryer on.
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