electro-magnetic hum - how to get rid?

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briomusic

briomusic

Well-known member
Joined
Mar 1, 2009
Messages
411
Location
London/Berlin
hi group.
just before xmas i started getting severe hum problems in my studio on all electric guitars and certain mics and mic lines.
to clarify: this is NOT a ground loop or anything related to my equipment or wiring. i verified this by walking around the studio with a guitar and a battery powered amp, having pulled out all the fuses, i still get a very noticable hum, with hotspots in certain areas and the guitar at certain angles.
even at the best spot the hum is louder than what is acceptable.

can anyone make a guess as to what might cause this? i.e. neighbours installing an MRI scanner?  ::)

is there anyway to measure magnetic interference and is this grounds for a complaint to the landlord? I am at my wits end on this one!

cheers
briomusic
 
I just read about a troubleshooter finding 7 Amps of current on a water pipe below the floor.  Try doing your test again, but very near the floor, walls and ceiling.  It would be hard to file a complaint against the landlord unless an un-safe condition was found.

See page 10:

http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf
 
just to reiterate, the hum does not originate from the electricity grid - the whole unit's electricity has been shot down, all fuses out.
no heaters, no lights (dimmed or otherwise), no sockets - nada.

i am walking around the building with a guitar hanging round my neck and a battery-operated amp tied to my belt, plus a battery flashlight so i don't run into things. the hum (50Hertz and assorted harmonics) is 'in the air', it is being picked up by the guitar which is not connected to the electricity grid by any means. it is tons louder than at home, and than it was in the same studio a month ago. something changed in the environment.

I wonder if there is a more accurate way of measuring this with a coil connected to an ac-voltmeter? I would just like to establish the direction of the magnetic waves and their origin (presumably the boundary of the building where they are strongest).

thanks for any advice
 
Keep walking with the guitar on your neck. ;D

Joking.

I am not aware of such equipment at least in affordable price range.

Only way to find out is to look into what has been changed in the environment and work backwards. Knock doors and ask people if they have anything new installed.

We still have a (small) Sony Trinitron TV in our bedroom. Some plants even abut a foot distance from it dry dead in a week.
 
In my earlier post, the problem can be from someone else's electricity. A co-worker discovered current on his water pipe.  It was from a neighbors home that had a broker neutral wire to the power company. The return neutral current went house to house through the water pipe then to the power co.neutral via my co-workers breaker box.
 
HI Brio,


  are you anywhere near railway or underground . .. had problems near underground(to put it mildly!)


  i find that dimmers are the biggest pain in the ass. If your neighbour has em, this could be the source.
 
Did symptoms show up the same time as the source? In other words, do you often use this battery powered guitar amp and notice the interference on it the same time as your grounded studio equipment?

I may be way off the mark but I would check your grounds. You say that your battery powered guitar amp is picking up this RF intererence but properly designed and shielded studio equipment should drain RF to earth ground. Your battery powered amp wouldn't.

Also, I'm no plumbing expert but has anyone in the neighbourhood had major plumbing work done? Many areas, electricians will ground your panel to the copper water pipe. If a key section of pipe was changed to plastic (you should probably have 10ft/3m of copper buried before it becomes plastic for a proper ground) you may not have a proper earth reference.

You could also call the power company and give them your address or the number off the pole with your transformer and ask if there's been any major work done that could affect you and if anyone else has complained.
 
Delta Sigma said:
Did symptoms show up the same time as the source? In other words, do you often use this battery powered guitar amp and notice the interference on it the same time as your grounded studio equipment?

I may be way off the mark but I would check your grounds. You say that your battery powered guitar amp is picking up this RF intererence but properly designed and shielded studio equipment should drain RF to earth ground. Your battery powered amp wouldn't.

Also, I'm no plumbing expert but has anyone in the neighbourhood had major plumbing work done? Many areas, electricians will ground your panel to the copper water pipe. If a key section of pipe was changed to plastic (you should probably have 10ft/3m of copper buried before it becomes plastic for a proper ground) you may not have a proper earth reference.

You could also call the power company and give them your address or the number off the pole with your transformer and ask if there's been any major work done that could affect you and if anyone else has complained.
Click to expand...

hi all, just checking back into this thread to let you all know I am checking up on replies and thankful for your thoughts and tips.

i do indeed have a major underground line close by, I would say 50m away, and no idea how much deeper (I am ground floor). however, the problem appeared recently - and as I found out today - is somewhat intermittent. Today the hum was normal/acceptable.

delta, the problem does not only appear with the battery amp, it started during normal recordings, with DIs Amps etc. I did the battery amp test to take my own electricity/grounding out of the equation. For me this established that the problem is airborne electro-magnetism and not related to my own electricity supply/grounding. It might well stem from neighbours electricity/facilities/machines etc.

I wonder if the chickenwire-faraday-cage is worth trying out, I have a vocal booth where I could try this, unfortunately it has 3 doors.

alternatively I am tempted to ignore the problem and hope it goes away  8)
 
briomusic said:
I wonder if the chickenwire-faraday-cage is worth trying out, I have a vocal booth where I could try this, unfortunately it has 3 doors.
Click to expand...

Since you are picking up this interference with a guitar pickup it is most likely a magnetic field. Unfortunately, a Faraday Shield will only stop very high frequency magnetic fields and will have no effect on 50Hz. What you need is a magnetic short circuit between the interference source and your equipment. The cheapest magnetic short I can think of is sheet steel.

Cheers

Ian
 

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