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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

Showing 1 response by gs5556

gs5556
1,209 posts
 
If you plugged everything into one outlet, then ground loops are not the problem. It is most likely caused by either external RF/EMI interference or power line noise which may be in the power coming into the house (yes, the power company xfmr can radiate the noise). Only an isolation transformer can solve this problem. If there are RF sources, then the long Romex runs pick up the noise. One method to solve this may be to put the romex into metallic tubing and ground the tubing by bonding it at the panel.

A second source of the problem could be if you have cable TV service and the incoming cable is not grounded to the house electrical ground or is not connected at all. This can cause ground loops within the house wiring from the CATV equipment.

Another problem could be the second ground. Try disconnecting the water pipe ground and see if there's a problem with just the ground rod connected. Then try the disconnecting only the ground rod. If either of these is the problem, get an electrician to confirm that they have been reconnected properly. Usually, two ground connections result in a voltage differences throughout the grounding system making it more likey to pick up stray currents.
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