Need Help With Nasty Hum

[silverhawk103]

Hello Fellow Slutz-

Before I begin to outline my problem, I just want to say that Gearslutz is a great, fantastic and generally groovy place to learn how great sound is massaged.

I was a lurker for the last 5 months, and through a zillion threads, I was led to purchase a Chandler TG Channel, a Distressor and a Soundelux U99, all of which I love beyond my wildest expectations when I first started thinking that a decent pre would make my Digital Performer experience as much fun and warmth as I used to have with a 57 plugged direct into a Teac 3340.

So, I am most grateful to all for their experience, opinions, shoot outs, diversions, links, and rants. Thank you, thank you, thank you. (by the way, my original budget when I started this process was $500. I have spent more than 10 times that, and don't regret a penny, though I'll be paying on it for awhile). My mic chain is glorious.

So, on to my nightmare. It's called hum and it showed up the very first time I went to record a bass track. The situation is that I live in an apartment that was wired in 1924, with two pairs of fat, ungrounded AC lines running under my floor and in my ceiling (my upstairs neighbor's power). And these lines put out magnetic fields that my pick-ups just eat up.

I have tried ground lifts, power conditioners, turning off the power to half my apartment, ferrite clamshells, and no matter what I do the fields are present wherever I am. There are a few null spots in my apartment, if I hold the guitar in an exact right position, at the exact height and angle. If I was a machine, I could play that way, but alas, I am all too human.

So, this human is screaming for help. Anyone have any ideas? (Please don't tell me to move, I love my home and it is super affordable.) I am thinking about shielding, but after hours and hours on the net have come up with nothing but a very expensive material ($18.95/linear foot) with no reliable info on what I would need to create a hum free playspace.

So, I humbly appeal to all the helpful geniuses in the house. Save me. Please.

Thanks, Steve

[Helsing]

Are you sure there isnt any grounded AC outlet in your apartment? Maybe there was a remodel done at some point and you can tie in there.

I would guess that your rig wants to see a solid earth ground somewhere. If you cant find one you might want to call out an electrician to help you add a ground point for your studio.

Jon Erickson

[silverhawk103]

Actually, there is one set of grounded outlets, at least according to the tester I bought. Among the many things I have tried is using that outlet with a power conditioner and an extension cord and going to various points in my apartment with a simple test rig and there was no spot where the pickups weren't generating hum and harmonics of hum.

I meant to mention in my original post, that the hum is much less noxious with humbuckings (duh!) but still present, and I can't imagine living without the option of that single coil sound.

I will be talking to an electrician, the question is who. If anyone knows an audio oriented electrician in LA, I'd be grateful for a connect.

[David Kulka]

If your hum is really getting into the guitar pickup, and it sounds like that's the case, the noise is going "though the air" and no sort of ground wire type solution is going to make any difference. Your problem is magnetic fields, not grounding.

Short of modifying the guitar with more shielding, or using a different guitar, or trying to put more space between the guitar and the offending wires, about the only solution I can offer is to have an electrician rewire the problem electrical circuits, tightly twisting the hot and neutral conductors. This will tend to make the hum field cancel out, which should reduce the noise level by quite a lot. I don't know if this is really a practical option for you, but it would probably work.

The hum field is generated by current through the power wires. Perhaps you can also get the noise level down by plugging your gear and appliances into different outlets or circuits. Turn off everything in your place except for bare minimum stuff you need on in order to monitor the noise. If it is lower, then start turning things back on one by one, to see which devices are the offenders. Of course, the real problem might be caused by something in a neighboring apartment, but at least you can got some answers by doing that test. Kaplan Electric in North Hollywood is very studio savvy. Good luck!

[paully]

Originally Posted by David Kulka

If your hum is really getting into the guitar pickup, and it sounds like that's the case, the noise is going "though the air" and no sort of ground wire type solution is going to make any difference. Your problem is magnetic fields, not grounding...

>>>>>>>>>>>>
I'll bet you're using a Fender, right? I have a REALLY quiet, well grounded studio, but I still have to shop around for a 'clean' spot to play a poorly shielded guitar.

Paul

[silverhawk103]

Thanks for getting back to me David and Paul. (I haven't quite mastered the "quote" thing yet).

The problem is definitely magnetic fields generated by wires. Unfortunately, even if I flip off the power at the breaker to half my apartment, I am still getting hum from across the room due to the wires which power the still working side and my upstairs neighbor's wires. Fun, huh... I have isolated everything, and the offending appliance seems to be the wiring itself.

I would be interested in hearing more about shielding the pickups. And I will call Kaplan Electric on Tuesday if I can track them down. Thanks for the tip.

And Paul, I'm actually playing one of Schecter's Diamond Series (Korean construction and very nice in my book) guitars with Duncan Humbuckers that I can flip into single coil when I am looking for the bite. I would love to have a good strat, but my gear dollars are all going to things that I don't have one of yet.

I hope the quiet spots in your studio are big enough to move around in. As I said, there are a few pretty quiet nodes in my place, but I can't move even a few degrees in any direction without getting hummed. I suppose I could bolt the guitar in place, but it doesn't seem like it would be much fun.

[Sounds Great]

Line the whole room with tin foil?

[silverhawk103]

I tried wrapping the guitar in tinfoil (do I sound desperate?) and it had no impact on the hum.

There is a foil I found online that has super low impedence to tempt magnetic fields away from the air, but the stuff costs $18.95 a linear foot and I don't know if I would have to line floor, ceiling and all 4 walls and if a slight gap would let the field through anyway.

I would love to hear from someone who has experience or knowledge of shielding an environment. I could build a booth and shield that, but I need to know that it would even do any good before heading down an expensive road.

There is a thing called a Farraday Cage that I have heard rumors about. I have heard that some have had success building a chicken wire cage that is grounded directly to earth, but it seems that it is only good on RF, and that it won't impact ELF (60 hz). Any experience with the cage?

[Helsing]

Try running a piece of wire from the 1/4" cable's shell to your bridge. Old trick that might help.

JE

[Sounds Great]

Originally Posted by Helsing

Try running a piece of wire from the 1/4" cable's shell to your bridge. Old trick that might help.

JE

I was having this problem for a while with a light dimmer. And this was with humbuckers. I found that the hum went down while I was touching the strings. Ended up with a wire around my wrist to the ground on the guitar.

[Helsing]

Heres a more professional way of doing it. These are readily available through computer parts supply houses, old school electronic parts houses, Frys, etc.

ESD Wriststrap

Jon Erickson

[Matt Syson]

Hi
Use your guitar pickup and 'map out' the areas of worst radiation. Go around your whole house at floor and ceiling level. Follow traces of high radiation and use 'post it' notes as markers. If you get a pattern that lines up with known wiring runs (your house or neighbours) then this could be tackled as mentioned above by getting the mains wires twisted. Assuming this can't happen then you need proper screening. We are talking sheet steel probably 1 - 2 mm thick. This will be HEAVY but is pretty cheap. You need to basically clad the whole studio area floor, walls and ceiling although depending on results of your tests earlier you may not need total enclosure. Aluminium foil does not work at screening this as the frequency is too low. A 'cage' of wire mesh might help but as it has so many holes it will not properly divert the low frequencies. Apart from the weight sheet steel is easier to make presentable (paint!). The steel plates should ideally be all welded throughout but cover plates over gaps will be sufficient.
A tough job!!
A small 'steel plated' booth may be more practical. Earthing should be done dor safety but it makes hardly and difference to electromagnetic shielding.
Go wave a pickup around and map out the hum field.
Matt S

[paully]

Originally Posted by silverhawk103

(I haven't quite mastered the "quote" thing yet)...

The problem is definitely magnetic fields generated by wires...

>>>>>>>>>>>
'Quotes' are easy. Click once on the 'quote' icon of the message you want, then when it arrives at the 'reply' box, 'cut' out any parts that you don't need using 'Edit'. Everything quoted should arrive in your 'reply' message box.

My studio is absolutely hum free, but not without some tweeks. Any guitar that gets near a computer or TV screen will hum. Avoid. As mentioned, phase-related dimmers ANYWHERE in the house will cause hum if they are on the same power leg (at the fuse box) as your studio line. Same with any motors; refrigerators, heating motors, flourencent ballasts, etc. Make sure that you're on the other AC leg. You might have to do some wire switching at the breaker box. AC wires in and of themselves won't create a magnetic field problem unless they cross an audio wire at a right angle, or unless they're carrying huge current. That's why Romex cable is acceptable. Keep AC and audio wires well seperated. Shielding the entire room is a good suggestion if the field is being generated outside of the studio, and if that's what it takes.. One final thought. Make sure the service has a real good 'earth' ground. Good luck with the 'sweet spot'.

Paul

[Matt Syson]

Sorry I have not got the hang of quotes either!
My studio is absolutely hum free, but not without some tweeks. Any guitar that gets near a computer or TV screen will hum. Avoid. As mentioned, phase-related dimmers ANYWHERE in the house will cause hum if they are on the same power leg (at the fuse box) as your studio line. Same with any motors; refrigerators, heating motors, flourencent ballasts, etc. Make sure that you're on the other AC leg. You might have to do some wire switching at the breaker box. AC wires in and of themselves won't create a magnetic field problem unless they cross an audio wire at a right angle,
Sorry, they SHOULD cross at right angles for minimum interference.
or unless they're carrying huge current. Any current is huge compared to a mic signal. I know this is voltage and not current but your mains is about +40dB and a mic signal is around -70dB. This is far from subtle!
That's why Romex cable is acceptable. Keep AC and audio wires well seperated. Shielding the entire room is a good suggestion if the field is being generated outside of the studio, and if that's what it takes.. One final thought. Make sure the service has a real good 'earth' ground.
A magnetically shielded room 'conducts' magnetism not strictly voltage so does not really need earthing although doing so will help reduce electrostatic interference and make it 'safe'. Good luck with the 'sweet spot'.

Matt S, with Paul's text mixed!

As I posted earlier, finding out where the field is coming from is an important step. It will take time but is otherwise free. Good hunting, Matt

[silverhawk103]

Thanks to all for their suggestions. The wire on the wrist had no substantial impact, but worth a try.

I have indeed mapped out the fields and they do coincide with the wires run under my floor and through my ceiling. I have calls out to Kaplan Electric (recommended in David Kulka's post)and a couple of other electricians who have some audio studio background, but I don't seem to be getting replies. I'm thinkin' holiday hiatus. But, nonetheless, the twisted pair approach would be my favorite, since it would kill the fields at their source and give me more freedom of movement than a magnetic shield approach would, but until I consult with an electrician, I don't know if the logistics and costs are realistically doable, especially since I rent.

If I go down the shielding route, I would probably have to go with the booth approach. Sheet steel is a whole lot cheaper than the magnetic shielding foil I found. I don't think that the weight would be a major factor if I build a booth. The only thing is that I am both engineering and performing, so I would need to be able to control my DAW with the Tranzport from Frontier Design and I'm wondering if the 2.4 GHZ signal would penetrate the shield so that I could record within the booth, although now that I think about it, I could have the receiver inside the booth with me and just run the USB by wire and hub.

So, the hunt for a solution goes on. I really appreciate all the people that have taken the time to get back to me. Wish me luck and Happy New Year to all. Keep the ideas comin', and if anyone else knows good studio electrician types in the LA area, I'd love the referral.

Peace

[Matt Syson]

Hi
Glad to hear you have at least mapped it out.
The usual culprit is two way switching of lights because the live and return may end up on oposite sides of the room making a masive loop. It is possible to sort it out but it involves running new cables so that at ALL points the current flowing to the lamp follows the return current including the stretch going to the switches.
Screened wires are unlikely to help as the frequency is low. You may be stumped because you are renting, in your own place you could just do it properly!
If you are really unlucky the building may be wired with power going different routes. This is against the code of practice in the UK but you are not here!
Another possibility is that someone has added some extra socket or light and just grabbed a live or neutral feed rather than taking it back to the supply box. All in all lots of fun!
Best of luck.
Matt S

[silverhawk103]

Thanks Matt. You have certainly convinced me that I need to have an electrition over to take a look. And I don't have any calling me back. Hate to go to the Yellow Pages.

Once again, anybody know a good audio savvy electrician in LA?

[paully]

Originally Posted by silverhawk103

Once again, anybody know a good audio savvy electrician in LA?

>>>>>>>>>>

Why not "balls up" and call/visit some of the local radio/TV stations. Ask if someone in the tech support end is available. Sometimes these guys will freelance or can refer you. A run-of-the-mill electrician is probably not going to have the answer that you need.

Paul

[TheSoundSteward]

One big clue to your problem is the date your house was built --1924.

It is likely that the power may on "tube and post". Long before Romex was invented the AC wiring was installed with bare wires about a foot apart on glass or ceramic insulators. Because of the huge spacing between the two current carrying conductors, there would be almost no cancellation at all of the magnetic field that surrounds each wire. A real nightmare of hum-inducing radiated magnetic field. If the neighbor's place is wired the same way, you will have the same problem from the top. If no current flows in the wires, there is no field. It makes it hard to record and play with the circuit breakers (fuses) off.
Using a battery powered amp (for a test) like the Radio shack audio amp $13 that runs on a 9 V battery would allow you to cut all the power to at least your place to confirm that the problem is magnetic radiation from the power wiring. It may be that the main tube and post feed goes up and down inside one of the walls, maybe an outside wall and then is tapped into at every floor to feed the apartment on that floor. You may be getting some magnetic radiation from the wall. If you can use a pickup to trace the path of the wires, it will give you some clue.


To Fix it.

AC wiring should have Hot and Neutral (and Ground) held in close proximity. Ideally the hot and neutral should be twisted and the ground wire not. Romex does a decent job of approximating this condition. Most of what I suggest is easy in new construction, but may be impossible in rework without making a big mess.
But I will give you my best shot at theory.

If you use Romex, you are done. Route it somewhere besides under/over where you play your guitar.

If you use individual wires, they must be put into conduit. Use STEEL, not aluminum, flex to contain the twisted wires. Nobody twists the wires, but the extra 1/2 hour you spend twisting will significantly reduce the radiated field, even in the Steel flex. Electricians hate Steel because they have to use a hacksaw to cut it instead of a pair of cutters and it is heavy. It is no more expensive than aluminum and it offers about 6 dB of magnetic shielding. Not much, but better than none which is what aluminum gives.

There is a product called BX armored cable which is a steel flex with the wires already twisted inside. You may have seen it used to wire up a garbage disposal under the sink, if yours doesn't have a cord and plug. This stuff already has steel and twisting going for it.

The worst situation is where the AC loops around the room as others have mentioned. In your case, perhaps after abandoning the AC wires that are under your floor you can re-route them near the walls which already have sockets in them.

All this is a royal pain, but it does significantly reduce the problem at the source.

Best wishes that you can find a relatively easy solution.

[Sounds Great]

I hate to suggest this but you may want to move?

[paully]

Originally Posted by Sounds Great

I hate to suggest this but you may want to move?

>>>>>>>>>>>>

That was my first thought after SoundSteward's reply. Not to sound glib, but if it turns out to be single-wired with stand-offs or old, cloth wrapped wire, some heavy renter's fire insurance would be my New Years resolution.

Paul

[silverhawk103]

Thanks again to all you helpful Slutz.

The wiring is indeed old, original, cloth wrapped, strung from ceramic insulaters, ancient wiring. There are two pair running about 4 inches between wires for a total run that is about 12 inches wide. And I do have renters insurance. A very good suggestion for any of us that have instruments and gear we wouldn't want to lose.

I really appreciate Steve Hogan's simple, easy to understand, explanation of what a solution would look like. I will be hunting down an electrician in the new year by calling studios, radio stations etc for a referal. And when I do , I will talk to him (or her, who knows?) about the BX armored cable. If it's pre-twisted and has steel conduit it should do the trick. Shouldn't be too difficult to reroute what's under my floor since there is access under the apartment. As to my neighbor's power supply, I guess a channel cut through my ceiling would do it without disrupting my neighbor except during the change over. And she's a gem and wouldn't have a problem with it. As for my landlord, I imagine he would be more than happy to have me pay for an electrical upgrade without getting his hands dirty or his wallet raided.

As for moving, not an option. Big, charming courtyard apartment with rent control. It is this low level of expense that makes it possible to take time off for music. Which is the point of setting up. What I might spend on an electrician and supplies would easily be made up in rent savings in a pretty short time.

Hope you all have a New Year celebration that is just the right amount of crazy fun and sets up 2006 for the best music you've ever made. (Best love, too!)

Peace,
Steve

[ionbri]

Hi there,

I was browsing the net and came across your hum problem. If you have established that there is a proper ground for your set-up,and yet are still experiencing hum or other noise problems in your system, you should look at buying a balanced AC power isolation unit. There is no doubt the technology works to establish a true 0V reference but also removes RF noise and other "dirt" that can be leaked into the equipment and utility ground.

I can give you more details if you would like to know more.

[Matt Syson]

Hi there
Fitting a balancing transformer is only the 'icing on the cake' and cannot really help much if your power wiring is badly laid out with large loops between live and return conductors. You may reduce the RF and other nasties on the power rails but from the discussion previous the guy is living in an apartment part wouund as a 1 turn transformer so having it balanced will make virtually no difference. The current flow and return must be as close together as possible, preferably twisted together for the WHOLE of the cable run. (this gets tricky in a real environment but is possible). If this is done then the system will be quiet, then, balancing the supply and filtering it would make it almost perfect.
Matt S

[soccerman58]

There is a thing called a Farraday Cage that I have heard rumors about. I have heard that some have had success building a chicken wire cage that is grounded directly to earth, but it seems that it is only good on RF, and that it won't impact ELF (60 hz). Any experience with the cage?[/QUOTE]

There is stuff on line about Faraday cages. A company I work for is into RFID tagging, and their stuff works on 433 MHZ (heavy TV and FM area). SOmetimes they have a problem that the reader can "see" through the ceiling to read tags on the floors above it. The answer to that is a Faraday cage. It's called a cage, which implies a sealed metal box, and indeed it can be a wholly-enclosing box.

But it can also just be a sheet of metal bent around the top of the reader, between it and the floor. And, it can be a fine mesh. It doesn't have to be heavy steel sheet I think (but my physics isn't great), that it depends on the frequency of the interference whether you need sheet or mesh.
And it has to be steel mesh tho
It's why you are safe in a car hit by lightning...the charge goes around the skin of the metal as it acts like a Faraday cage.
Phil

[dkatz42]

Originally Posted by paully

AC wires in and of themselves won't create a magnetic field problem unless they cross an audio wire at a right angle

You've got that backwards; the magnetic induction is highest when the conductors are run parallel, and lowest when they are at right angles.

[paully]

Originally Posted by dkatz42

You've got that backwards; the magnetic induction is highest when the conductors are run parallel, and lowest when they are at right angles.

>>>>>>>>>>>>>>>>>
Hey, when you're right, your right. Matt corrected that one back in December! Good eyes, though.

BTW, if by induction you mean a magnetic field, then didn't you just re-state my original mistake? LOL


Paul

[apeak]

Silverhawk,

Here's one more trick that might work:

Hang your guitar up on a stand at approximately the same level and at the same position that it would be when you're playing it. Plug it in and record just the hum for the duration of the song you are working on. Then record your guitar track. Now flip the phase of the hum track and mix it in with the guitar track. You might have to move the hum track very slightly back or forward in time and play with the volume level, but you might be able to cancel out most of the hum this way.


Tony DeSilva

[David Kulka]

Tony, have you successfully done this? The AC line frequency is stable, but I don't think it's that stable. Seems like it would be awfully hard to achieve "sync" and once you did, it might drift out before long. Also the waveform of the hum would be influenced by the guitarist moving around and other random thiings that would be hard to replicate on a second pass. In the end the noise might increase rather than cancelling out.

[Matt Syson]

Hi
Sorry to hear you haven't got far yet.
You only have 2 real options (if you don't want to move).
Get a full rewire of your place AND adjacent apartments.
Get friendly with a steel stockholder and invest in SERIOUS iron, talking 1/8 inch plate to cover the whole surface of the room (ceiling, walls and floor) with no gaps. Some seams may need to be welded, certainly they must overlap to make a continuous loop around the room. Seriously the best plan is get some rewiring done and if it is from 1924 it would probably be a good idea on safety grounds to get it 'up to spec'.
Matt S