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Electrical issue

I have an electrical issue/s that I could use some help with. It's a hum issue, but after exhaustive research here and on AA I still cannot figure it out. I have 4 dedicated lines for my stereo run approximately 75 feet with 10/2 romex all connected to Porter Ports. I own Von Schweikert DB-99's, which have a powered sub built in. I have tried lifting the grounds on all the equipment except one(and every conceivable variation,I think), I've tried plugging everything into a power strip and then that into just one outlet, I've even tried using other outlets(not dedicated). In the end, if I disconnect everything and just plug the speaker into the wall with no other connections I will get a hum thru the woofer only. I have even put a PS Audio P500 between the speaker and the outlet to see if it made any difference to the hum, but no luck. If I leave the speaker wires connected and turn on the main amp then I will hear hum thru all the speakers(tweeter/mid/woofer).

I called VS and spoke with Kevin and he said that the signal is split in the speaker before the sub amp which would suggest that the hum is coming from my electrical system rather than my equipment. IOW, if I heard hum only thru the woofer and not the other drivers when the main amp is connected then there could be a problem with the sub amp, but this is not the case.

My house is new and the electrical and grounding system seem to be in good shape. I have checked every outlet I could find with a polarity/ground checker and did not find any problems. My panel is grounded both to the water line and a spiral rod buried next to the house. According to the builder these are acceptable to code here in Austin, Tx.

The only thing that seems odd is that when my A/C turns on, and sometimes my TV, the lights will dim for a second. I had the builder double check all the connections and made sure the proper gauge of wire etc. was used to hook up the A/C, but nothing seems to be wrong. Is it perhaps the Transformer on the pole outside? It's definitely old as it looks a bit rusty up there(new house - old neighborhood).

The hum is not particularily loud, but i can here from my listening position 10 feet away when no music is playing. I appreciate any help you may have to offer, and I'll answer as many questions as you have because I'd really like to solve this.

Thanks,
Matt
mab33
nerspellsner
41 posts
 
Call your power company and have them test the transformer and install a data recorder at your meter if the CATV and phone grounds are not the problem. CATV and phone must be connected to the same ground rod as the service grounding conductor. Most power companies are required to provide clean power to the service. If you have a well, the ground rod or rods are your ground and the water pipes are not. The pipes are bonded to the ground for saftey. Never ever disconnect the ground wire of the service with the main breaker on. Turn off the main breaker before disconnecting the service grounding conductor. You could get electricuted if you dont. Your lights will dim for 1-3 seconds no matter what the size of the transformer when you AC starts. What you are hearing is probably a 60Hz hum. The hum could be coming in through the neutral from the transformer. If you lift (remove) grounds on your equipment with metal housings, you have a small chance of getting killed. If the power company will not help you do this. Hire an electrician and ask him to connect an outlet directly to the line (street)side of the meter socket. Plug your subwoofer or you whole system into that outlet. If it still hums, complain to your power company about bad power and have them fix it.

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nathanso
25 posts
 
Noisy power poles are a longtime nemesis for ham radio operators whose sensitive receivers try to pull weak signals from the ether. An arcing insulator on the 12KV lines atop most residential and rural neighborhood power poles can spew RFI across hundreds of Mhz.

Depending on what mode you listen in (AM, FM, SSB) it sounds like a grinding buzz, or your basic 60-cycle hum. There's a pole 2-300 yards from our house that has been causing me no end of grief, and the local power company doesn't give a rat's ass about it. Last year I complained formally and after 7-months they dispatched a truck to "rebuild" the entire top of the pole. The parts all looked the same when I got home from work that day, and of course, the noise was still there.

Use a portable AM radio tuned to an empty spot on the AM band. Walk down your street from power pole to power pole noting if static/hum increases as you approach/depart each pole. If a pole has guy wires, twang the wires and listen for noise (it shouldn't cause any). Bring a pad of paper and pen as you'll need to note the pole ID numbers to lodge your formal complaint. Some utilities are pretty good about fixing these things; others, like PG&E here in NorCal, are not.

If you end up finding a noisy pole and file a formal complaint, I strongly recommend you log each and every contact you make with your utility as you may need it later when the issue has dragged on longer than you ever imagined possible.

I have a hum problem on my newly assembled high-end system and I'm hoping it's something *inside* my house and not something *outside* in PG&E's domain.
mab33 OP
101 posts
 
The power company made it out today and although they couldn't find a voltage problem they installed a data recorder and said they'd be back in a few days. They agreed that the transformer was very old and possibly undersized as well. He said they would turn in a work order to replace it after they finished recording it's activity. Fairly positive visit, but we'll see how it turns out. Sometime next week my electrician is going to come over and install the iso transformer as well so pretty soon I should have an answer. Thanks for your help so far and I'll let you know how things work out.
mab33 OP
101 posts
 
The electric company let me down. They said that, although my voltage did drop below 120V when the A/C turned on, it was otherwise operating normally. They also said that noise on the line was not their problem and they weren't willing to use their resources to track it down. They suggested getting a "Starter Kit" for my A/C, but I know nothing about these so I'll have to do some research. They offered no real help with the hum. I'm going to try and schedule some time with the electrician to install the Iso tranny and see if that helps. After that I'll try and run the Romex thru metallic tubing that I ground to the subpanel. Eventually, I may solve this:-).
nsgarch's avatar
nsgarch
2,524 posts
 
A heavy duty starter kit is a good thing to have on your A/C anyway (though I don't think it will solve your noise problem) It's an especially good thing to have if you've got children who play with the thermostat!
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