Recording studio 60hz noise

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Hello all,

I'm posting this in the education section because I'm curious about the theory that goes into solving noise problems (EM in the air).

Here is my scenario: I am renting an old house, probably built in the 1930's. It has knob and tube wiring in the attic, and most of the outlets are ungrounded.

I set up a little recording studio in one of the rooms which basically consists of a computer, some audio interface equipment, and of course, microphones. I temporarily grounded the outlet that powers all the studio gear using an adapter and sending a wire to a copper pipe that already had another ground wire attached (I believe for CATV). It passed outlet tester test, but I'm not sure how great the ground really is.

I find single coil microphones (like the SM57 for those familiar) and electric guitars with single coil pickups have so much 60 cycle noise that they are unusable in this room. Condenser microphones seems to be immune. I am able to trace where the noise is most intense by moving the mic around, and of course it is toward the ceiling, where house electrical wiring is overhead.

I ran the whole system off battery and all the 60 cycle noise disappeared. I also tried running the system ungrounded, and I still have the exact same noise.

I've never had so much difficulty with house wiring noise before. All the equipment I'm using is the same or similar that I've used in other residences without any issues (several of equipment has SMPS). I'm just renting, and definitely won't live here for very long, so I realize I probably can't do anything to fix the noise.

However, I want to know: why is EM noise such a problem this time for me? People tell me "you need better grounding." It's obvious for safety reasons that this house needs a new electrical system, proper grounding/bonding/ground rods, etc. but it's not obvious to me how new wiring would help with this particular EM noise problem. If the circuits were re-ran with newer insulated wiring, would this "trap" the EM? What the physical mechanism that is allowing noise to be so rampant in this dwelling, but not be a problem with new wiring yet all else equal?

Thanks so much in advance for any theories!
 
Attached are photos of the attic showing the knob/tube wiring.
 

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dfmischler

Senior Member
Location
Western NY
Occupation
Facilities Manager
My initial thought was that the unbalanced currents from the Knob and Tube wiring was giving you a strong EM field. And that makes perfect sense with the problems with single-coil pickups, etc. But I don't know why those problems would go away when you run on batteries.
 

ActionDave

Chief Moderator
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Location
Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
Hello all,

However, I want to know: why is EM noise such a problem this time for me? People tell me "you need better grounding." It's obvious for safety reasons that this house needs a new electrical system, proper grounding/bonding/ground rods, etc. but it's not obvious to me how new wiring would help with this particular EM noise problem. If the circuits were re-ran with newer insulated wiring, would this "trap" the EM? What the physical mechanism that is allowing noise to be so rampant in this dwelling, but not be a problem with new wiring yet all else equal?

Thanks so much in advance for any theories!
People always reccomend better grounding just like doctors always prescribe antibiotics, even when the problem is a virus.

New wiring would "trap" the noise in the sense that the conductors would be close to each other and the magnetic fields would cancel each other out. With K&T the conductors are so far apart from each other your room is like an ocean of magnetic waves and no grounding of any sort will make that go away.
 

GoldDigger

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Location
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If the equipment uses polarized plugs (2 or 3 conductor), it may expect the neutral to be at a potential close to ground. In that case if there is a high resistance in the neutral (or the hot and neutral are reversed in the receptacle) you might pick up him from that.
Do you have to operate all equipment off battery or just some of the components?
Is it a 60Hz sinusoid or actually 120Hz "buzz" which would indicate noise from a non linear load like a power supply, dimmer or old CFL?
Have you tried turning off all other circuits in the house to see if there is a noise source there?
You seem familiar with the fact that the magnetic field from K&T extends much further from the wires because of the separation of the opposing currents. But that should have no effect on conducted noise via the power cords.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
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EC
My initial thought was that the unbalanced currents from the Knob and Tube wiring was giving you a strong EM field. And that makes perfect sense with the problems with single-coil pickups, etc. But I don't know why those problems would go away when you run on batteries.

Possibly because the equipment in the room is supplied by the K&T wiring nearby. Running on battery power=no current through the wiring=no EM field. So my thought is to run a temporary circuit directly from a receptacle installed at the service panel with something like an SJ cord extension cord that has twisted conductors and see what happens.

-Hal
 
Thank you all for your replies!

Yes, I should've explained better: The whole system is on a UPS. I hit the main disconnect to the house and ran the system off backup battery with absolutely no noise- this is how I determined that it was the house wiring causing the noise (picked up by sensitive single coil microphones/guitars).

It's definitely a buzz, a signature of triplen harmonics from all the non-linear load in the studio (computer and equipment power supplies). The UPS's current draw actually noticeably contributes to the buzz. I tried unplugging the UPS and hooked all the studio equipment up with just a power strip instead- still a significant buzz on the microphone. So, I would say the wiring itself is the issue even though it can be slightly helped if I shed some of the nonlinear load (which is basically impossible).

I don't have any ground loop problems or noise being injected onto wires- it's all EM air getting into single coil mics. (Condenser mics are not affected).

This house is 120V only- no split phase. Can some one please explain to be what is meant by "balanced wiring" in this case? Do you mean (with a typical 240/120V system) running the A and B circuits next to each other to cancel EMI? How does balanced wiring come into play if you only have basically (1) 120V circuit in the whole house?

Thanks again for any and all spitball replies!
 
Possibly because the equipment in the room is supplied by the K&T wiring nearby. Running on battery power=no current through the wiring=no EM field. So my thought is to run a temporary circuit directly from a receptacle installed at the service panel with something like an SJ cord extension cord that has twisted conductors and see what happens.

-Hal

Thanks, this is a great idea. What I'll try is to run an extension cord from a part of the house's circuit that I know doesn't go over this room, and see if the noise goes away or at least changes.

You seem familiar with the fact that the magnetic field from K&T extends much further from the wires because of the separation of the opposing currents.

With K&T the conductors are so far apart from each other your room is like an ocean of magnetic waves


This is very interesting! So do normal wiring schemes have circuits running in opposite directions (or same directions but opposite phases), close together, for this very reason? (Sorry I don't normally get to work with the details of wiring methods).
 

GoldDigger

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Location
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Retired PV System Designer
Possibly balanced wiring refers to the "technical" power system where you feed from a center tapped isolated 120V secondary so you have 60V to ground on both hot and "neutral".
Or it could simply be the process of running all conductors of the circuit as close as possible to each other.
 

Smart $

Esteemed Member
Location
Ohio
Thanks, this is a great idea. What I'll try is to run an extension cord from a part of the house's circuit that I know doesn't go over this room, and see if the noise goes away or at least changes.




This is very interesting! So do normal wiring schemes have circuits running in opposite directions (or same directions but opposite phases), close together, for this very reason? (Sorry I don't normally get to work with the details of wiring methods).[/COLOR]
Do you get any "hum" or "buzz" with the mics unplugged? Test at both ends of cables; all mics, cables at same time. This will confirm whether "noise" is being picked up by mic or cable or at preamp level (mic input).

If your cables are XLR, that should be balanced input.
 
Here's a quickie on balanced vs. unbalanced signals...

http://thehub.musiciansfriend.com/tech-tips/unbalanced-versus-balanced-i-o-and-how-to-work-with-them

You can find many others on the matter using "balanced vs. unbalanced audio" as a search term. Balanced has much better external "noise" rejection.

Thanks- all my lines are balanced (XLR or TRS), and I'm quite familiar with "balanced" in terms of signal wiring, differential inputs into amplifiers, etc. though it's the "balancing" of the power circuits that I'm most curious about now (though not with a +60/-60 balanced sourced though, hehe).
 

Smart $

Esteemed Member
Location
Ohio
Thanks- all my lines are balanced (XLR or TRS), and I'm quite familiar with "balanced" in terms of signal wiring, differential inputs into amplifiers, etc. though it's the "balancing" of the power circuits that I'm most curious about now (though not with a +60/-60 balanced sourced though, hehe).
Why not? That's the only way you're going to get it for 120VAC-powered equipment.

The only other balancing would be on a 120/240VAC split phase system, and that would not fix any signal-level audio "noise" problems.
 
Do you get any "hum" or "buzz" with the mics unplugged? Test at both ends of cables; all mics, cables at same time. This will confirm whether "noise" is being picked up by mic or cable or at preamp level (mic input).

If your cables are XLR, that should be balanced input.

The buzz is definitely picked up at the mic, and only single coil mics at that (which have a small part of their circuit that is inherently unbalanced). Without anything plugged in, I pick up no noise- none of my preamps or other equipment are humming by themselves, which says a lot about the quality of the equipment really!
 
Why not? That's the only way you're going to get it for 120VAC-powered equipment.

The only other balancing would be on a 120/240VAC split phase system, and that would not fix any signal-level audio "noise" problems.

I meant to say- what is the proper way to wire a music recording studio without using a balanced source +60/-60 (for simplicity sake)? And it would seem the answer is "carefully," that is, run opposing circuits close to each other, and be mindful of where your loads are plugged in.

The reason why is because, well, I've recorded in plenty of studios that did not have balanced +60/-60, and never had such an issue, so for the sake of simplicity, I wanted to limit the amount of variables and find out what exactly those other studios did right, and what exactly is going wrong in my space.
 

Smart $

Esteemed Member
Location
Ohio
The buzz is definitely picked up at the mic, and only single coil mics at that (which have a small part of their circuit that is inherently unbalanced). Without anything plugged in, I pick up no noise- none of my preamps or other equipment are humming by themselves, which says a lot about the quality of the equipment really!
If this be the case, I don't think there is anything you can do short of re-wiring the house... or turn everything off that is powered by the K&T wiring, perhaps power those loads or substitutes (e.g. plug-in lighting) with extension cords from panel location as suggested.
 

Smart $

Esteemed Member
Location
Ohio
I meant to say- what is the proper way to wire a music recording studio without using a balanced source +60/-60 (for simplicity sake)? And it would seem the answer is "carefully," that is, run opposing circuits close to each other, and be mindful of where your loads are plugged in.

The reason why is because, well, I've recorded in plenty of studios that did not have balanced +60/-60, and never had such an issue, so for the sake of simplicity, I wanted to limit the amount of variables and find out what exactly those other studios did right, and what exactly is going wrong in my space.
Actual studios (without a balanced power system) typically use metallic wiring methods (EMT, MC/AC, metal outlet boxes, etc.).
 
If this be the case, I don't think there is anything you can do short of re-wiring the house... or turn everything off that is powered by the K&T wiring, perhaps power those loads or substitutes (e.g. plug-in lighting) with extension cords from panel location as suggested.

Thanks.

I just now got it through my thick skull that the opposite currents that are "so far apart with K&T wiring" is because the hot and neutral wires are so far apart. (I was thinking of two circuits being far apart or close together, running opposite directions, etc. but we're talking about only ONE circuit whose hot/neutral should be very close together, cancelling EMI, which is obviously cured with modern wiring like romex or hot/neutral ran close together in a conduit, etc) :slaphead:

Thanks everyone for your help- I feel educated- I'll let you know how the extension cord experiment goes!
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
On a side note. Years ago I bought some Permatex copper gasket seal, and painted the electronics cavity of my beautiful 1969 Stratocaster. Along with the foil tape that is original in the Strat, it helped to quell some of that single coil buzz. The rest just adds character.:D
 
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