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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
nsgarch's avatar
nsgarch
2,524 posts
 
If you plugged everything into one oulet, you have ground loops galore!! You may not have a ground loop thru the in-wall ground wire(s) but so what? Trace the path: from AC ground to component to interconnects to next component and back to AC ground, and so on and so on and so on with each source component thru the preamp thru the amp and thru any powered speakers/subs.

Lift all ground plugs except the preamp so you have a single path from all equipment back to ground.
mab33 OP
101 posts
 
Hi,

Thanks for all the info and ideas. Although I'm pretty sure I had already tried lifting the grounds on everything but the preamp, I tried it again, but the hum persists. Considering that the speaker will hum even if it is not connected to anything, only plugged in to the wall to power the subamp, it seems unlikely/impossible to be a ground loop associated with the rest of the equipment.

I have been researching the subpanel/isolation transformer idea for a month or two now and managed to pick up a 5Kva Topaz transformer on the cheap, so I'll probably go this route at some point in the near future.

I suppose I'll need to call the utility co. and ask them to replace the transformer leading to my house. Is this something I'm likely to meet resistance with?

With respect to Gs5556's response, What does EMI/RFI sound like? Kind of naive question I guess, but does it sound like 60Hz hum? What differentiates it? Second, I do have cable and I remember the installation guys hooking up some kind of grounding to my electrical panel, but I think it's mounted to the outside of the box. There is no cable hooked up to any part of the stereo however. And last, I did actually disconnect the water pipe ground a while back to see if it would make any difference, but it didn't. I never tried disconnecting the other ground though while leaving the water pipe connected so I'll give that a try.

I really appreciate everybody's help!

Matt
nsgarch's avatar
nsgarch
2,524 posts
 
Matt, a lot of subs have a very faint 60 cycle hum/buzz when plugged in alone with no other connections. Something in those class D amps they use. You might want to check with the manufacturer though.
mab33 OP
101 posts
 
Nsgarch,

It's actually a 300W Class A/B solid state amp. If it was only the sub amp then the midrange and tweeter shouldn't be effected according to Kevin at VSA. We'll see...

Matt
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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