Extreme EMI

OK, maybe this isn't exactly the right forum for this question, but I figure someone here must have dealt with this kind of thing before, so here goes.

I live in a single-family house, around 4000 sq ft.  I have extreme problems with EMI.  All of my guitars, single-coil and humbuckers, shielded or not, pick it up.  It sounds like a buzz saw, except when I orient my guitar so it points in one direction, where it nulls out.  It's very clear that it nulls out in the one direction, and exactly 90o away is the worst.  I haven't tested everywhere, but the EMI seems to be pretty uniform. 

The thing is, I've completely eliminated any source for the EMI inside the house.  I did an experiment today where I plugged my Strat into my battery-powered Pignose amp with an overdrive pedal, shut the master breaker off, and unplugged the phone connection at the source.  It was just as loud as ever.

What could it be?  I was thinking it could be the meter.  Also, there's a neighborhood transformer on the property on the other side of the house (100+ ft away).  Are there standards for this kind of emission?  It it's the meter or the neighborhood transformer, is there any chance I'll have a servicible claim with the electric company? (I'm in the US)  Is there any chance of putting up some kind of effective shielding against the interference.  Help!

Do you live in an area where they use broadband over powerlines (BPL)?

hmm maybe there is a earth grounding issue?  That transformer would not be able to transmit 60hz that far.

Maybe wires in the wall? Electronic dimmer switches? <--- these are nasties.
A ceiling fan? or anything with AC motors on it?
Old TV set?

owel said:

Maybe wires in the wall? Electronic dimmer switches? <--- these are nasties.
A ceiling fan? or anything with AC motors on it?
Old TV set?

Click to expand...

No he said he turned the main breaker off.  It has to pretty much be external magnetic fields (i.e., outside of the house).

Pretty intense.  That transformer at 100' sounds intriguing.  What I would do is travel about with your batt operated amp and guitar and seek out the source.  Should be pretty obvious when you close in on it.

Ooops, missed that part. Yeah, that line transformer could be a suspect.

I worked at a studio where we had problems with external EMI.  It turned out to be the electric mass transit trains ALMOST 2 BLOCKS AWAY!

What I would do
Using the battery power amp and your guitar like you have done

Find the null in one spot of your house and/or yard note your headstock guitar direction use a piece of paper and place it in the spot with an line drawn for the null direction

more to another spot in the house and/or yard find null and direction 20 or more feet mark the spot and direction

find where the lines meet in the distance.  It could be along the length of the guitar in both directions

This uses the guitar and amp as a direction finder I would guess single coils might work the best.

That's a good suggestion, although, I think the direction may be perpendicular to the length of the guitar.  I have a good hunch it's the house meter, rather than the transformer.  The transformer side of the house seems to be quieter overall.

Oh, and to the previous question, no, no overhead power lines in my neighborhood.  Everything is underground.

Use a battery AM radio (boombox?) tuned-off a station.  They have a semi-directional dipole antenna inside which you can use as a rough direction tool.  Walk towards the louder buzz and find the culprit.  So much EMI is not good for the body or soul, either. . .
If everything is buried, is the main mains feed under your house?
It can also be RF- any towers within a mile?  Any heavy industry around?
Mike
PS: reminds me of the stories about people with huge coils in the barn under the high tension runs, sapping electricity from the grid.  "The man" can always find them because of the extra load on the system.

Hello,
It remembers me a crazy story that happened at a new studio, nearly 20 years ago...
They experienced the EXACT same situation as you...  could not record any guitar in the studio, so much hum/buzz/noises...and it was also making the mix bus of their SSL humming a bit...
Like you, there was also a big transformer from the electrical company near the studio, and we all thought it was coming from there, but it was not.
We were several techs to cut our teeth on the problem, before one discovered the culprit : a BIG mains cable running... 15.000 volts ( !!! ) had been fitted a few inches (!) under the floor of the studio, to power a building that had got renovation, and this building needed a new mains power cable.
The walking distance from the transformer to the building entrance is about 300 meters.
What happened ? The workers from the electrical company " cut " their way ILLEGALLY on the basement floor of another building, where the studio was later built, and then "spared" 250 meters of very expensive wire, compared to the "normal" way ( cutting a deep slot inside the street ground, and running the cable around the block )  ! .
When the manager of the electrical company district arrived to the studio he was quite afraid of what he discovered...
Kafka, may be some wires from the transformer are running ( too ) close to your house underground ?
Just my 2 cents...
Guy

Hi, thanks for all your responses.  I have a strong suspicion that it's the utility meter, although I'm not 100% sure about it.  From the position of the nulls, it doesn't exactly seem right.  I'm thinking that some other iron in the vicinity - perhaps a water main, is distorting the field so it doesn't exactly center around the meter.  It's a little hard to tell with a Strat and a Pignose.  I took a large steel amp chassis that I had and put it between the guitar and the meter, and it seemed to cut most of the higher frequency buzz, so it seems that could be it.  If I can get it down to a constant 60Hz hum, I can probably handle the sound in the mix.  I'll just have to stand perfectly still when I play bass.

I ordered an AC Gaussmeter so I can try to determine exactly what the source is.  I've been looking into putting some magnetic shielding up, although I have my doubts as to how effective it will be.  Unfortunately, other than professional consultants that do shielding for medical and scientific purposes, it seems that most of the businesses that supply shielding are also selling stuff like EMI-resistant underwear and paranormal research tools!  I hate doing business with someone who deals in snake-oil, but they seem to be the main retail suppliers.

Just a thought, but there is one thing that might cause this in the context of a US install.

Do you have any sub panels in your building?
If so, do they (correctly) have the neutral/earth commoning link removed? In US electrical installs this must only be fitted at panel connected directly to the incoming supply.

If this link is fitted in a sub panel then part of the neutral current will flow in the ground network, which will massively increase the loop area and thus the interference (it is also not compliant with the NEC).

As to shielding low frequency magnetic fields, forget it, you are talking megabucks to do anything that will work, if I was really desperate I might try something with large helmholtz coils and phase shift networks to create a localised null, but that sort of thing is a nightmare to engineer.

Regards, Dan.

I've traced out the magnetic field, and it's very interesting.  With the power completely shut off at the main breaker, there wasn't any significant reduction in the field.

It turns out there's a very high magnetic field around the water pipes, due to a net current through them.  There's a 27mG field at 8" coming off my main water pipe into the building.  Most significant to my recording workspace, there's a copper pipe* from my furnace to the AC unit outside, that has around a 7mG field at around 8".  There's also 3-5mG in many parts of the house that are near the central plumbing.  When I get a room or so away from this area, or upstairs, that field drops to .1-.3mG.  When I go outside, I can exactly trace the water main into the house with the Gaussmeter, and I'm picking up around 1.5mG at ground level.

I'm not sure these levels are acceptable living standards, let alone recording.  One solution I've heard about is to have an insulating connector between the house and the water main.  This seams reasonable, but it's easy for solutions to seem correct before you know what you're talking about.



* I don't think this pipe actually carries water.  I think it carries the coolant from the AC unit outside to the condenser inside.  I measured there was minimal resistance between it and the water pipes.  So, electrically, it's effectively part of the water system.

Electric company dirt-ground is failed. The line down the street is grounded THROUGH your house and out to the water utility.

Any lightning-hit on your street will also flow through your house.

It also sounds like the ONLY grounding-electrode at your house is the underground water pipe, although it is possible you have a dirt-rod which "works" but is only taking 1% because it is so very much smaller than the water company's pipes.

> an insulating connector between the house and the water main

When you disconnect the water pipe to insert a bushing, you will be electrocuted. So will the next water-company tech who replaces your water meter.

I think you and the water company need to YELL at the electric company.

I think this probably also explains why I lose my GFCI sockets during every electrical storm, as well as why my AC pops the circuit breaker so frequently during the summer.

BTW, the reason that I specified 8" measurements is that I read that at that distance, mG = Amps.  Is this correct?  Do I really have 27 Amps of current going through my water main?  Good God.  That's unreal.

If this is a dirt failure, it would be the third confirmed time ive seen this. the first time we ran a hose on the ground rod and the bulding got quiet immediately. second time was at the "big" studio in LA and they swore that it wasnt the "dirt" until a few days later when they ran a hose on the ground rod. I suggested the ground failure but they brushed me off, new guy and all. I have since learned that large portions of the US have different soil hence different ground potentials. Very interesting. Our dirt here is sand and the moisture can just seep away after months of brutal heat and no rain.

kafka said:

BTW, the reason that I specified 8" measurements is that I read that at that distance, mG = Amps.  Is this correct?  Do I really have 27 Amps of current going through my water main?  Good God.  That's unreal.

Click to expand...

OK, I verified, at 8", mG / 10 = Amps.

I also was able to see 12 Amps on my water main, which is the most I've seen.  I also saw 7 Amps on my neighbor's water main around the same time.

Downstream neutral problem.  I got my service provider to come out twice this week.  The first time they didn't really confirm anything, and sort of brushed off the issue of the current on the water main.  I found that it was mostly a question of getting the right person on the phone.  Those who understood what I was talking about took it pretty seriously.

The end result, the neighborhood neutral looks bad.  They put a temporary neutral on my and my neighbor's house, and said they are probably going to dig up the old neutral and replace it in the next week or so.

I did some testing, and I now have 0.00 Amps on the water main, and 0.0-0.1 mG in the middle of my main room.

Congrats!

This has been a fascinating thread to follow.