Microphone Buzz On Rotation - Magnetic Interference

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dawsonaudio

Well-known member
Joined
Dec 17, 2011
Messages
115
I've been getting a buzzing sound coming from my sm57 and/or beyer M160 ribbon mics. Seems to go away a little when rotating the mic in my room. For example, pointed at 12 and 6 o'clock help reduce the buzz and 3 and 9 o'clock create the largest buzz. I also notice my fender strat buzzes more at certain angles in my room when I'm playing. My room is in my garage with designated circuit/s coming from the main panel. Turning all the power off except my studio power didn't solve the problem.

Is there a more thorough way of locating the problem and/or removing the interference entirely...

The chain is mic, api preamp into chandler mini mixer. Replaced cable with no change to buzzing.

Thanks for any advice here.

Nate
 
With the long cable attached, sitting at my desk in the listening position, with the 57 pointed at 12 o'clock, hum/buzz noise is apparent.  My chain is 57 into mic preamp into mixer...out of mixer into headphone amp and powered Event SP8's... Mic preamp is full on.    The noise it at it's quietest at 10 and 4 o'clock and at it's greatest at 1 and 7 o'clock.  Turning off the monitor's helped reduce the noise a little.  Turning the monitors back on increased the hum/noise a bit. 

From here, I took the 57 and noticed that the hum was extreme next to the monitors when they were on.  Must be a large magnetic field coming off them at the sides.  I also took the mic to a subpanel outside the studio and touched the conduit and the buzzing sound was really apparent. 

I should say that my studio wiring is looped around all four walls.  Not sure if this is causing a magnetic "loop" of some kind which is creating this weird interference.  Considering eliminated electrical wiring in all four walls and having all power terminate on one side closest to the subpanel.  Not sure if this will help eliminate some interference. 
 
dawsonaudio said:
I should say that my studio wiring is looped around all four walls.  Not sure if this is causing a magnetic "loop" of some kind which is creating this weird interference.  Considering eliminated electrical wiring in all four walls and having all power terminate on one side closest to the subpanel.  Not sure if this will help eliminate some interference.
It's not that weird. Clearly it's mains. The more current running through the wires, the greater the magnetic field. The ideal arrangement is to minimize high current devices in areas where microphones and guitars and other coil based devices will be used.  And, wherever you must have power, you want currents to return very close to the path from which they came so that the fields cancel. And shielded cables power cables (called BX here in the US) might help too.

So you want to get away from any high currents. You suggested you're next to a panel in a garage? Is this for a house? There may be no solution for that. All of the current for refrigerators and AC and TVs and such throughout the house are going to be going through that panel. Do you have a basement? If the panel is in the garage then a basement with no panel is even better.

It might help to re-arrange wires. Don't plug things into different wall sockets. If you have a heavy duty socket directly connected to the panel, then attach an equally heavy duty cord to that socket and run it some distance over to your desk with the monitors and such. At the other end of the cord put a heavy duty 4 socket floor box. Then attach extensions and power strips that fan out from that one point. Try to power all gear that will be patched together to the same branch point. Meaning try not to connect ground loops. For example, if you have a guitar amp connected to one power strip and a rack effect unit on different power strip and then you try to connect the send of the amp to an input of the effect unit, you now have a big loop. If there's any difference in grounds or if there's a lot of noise on one ground (more current means more noise) that loop can cause noise.

Also try running separate cords from the panel to high current gear that doesn't need to interconnect (meaning differences in ground potentials won't matter as much). Guitar amps would be a great candidate for example. You might also try a separate line for your monitors. Technically you will of course interconnect to your board but if the interconnect is balanced, it may pay to power them separately but share signal ground.

So with some careful re-arrangement you might be able to make things better. Build it up incrementally and see what causes noise. Start with a mic-pre and a headphone amp and turn everything else off (especially computers).

The best possible solution would be to put computers with fans and high current stuff like monitors in one room and then you have a bundle of cables into a very quiet place with no fans and accoustic treatments and no high currents.
 
I  would look for a WATER PIPE under the slab. GROUND CURRENTS flowing can cause a big field. Get a pickup coil (current transformer, small toroid, or your mic) and a long cable and hunt for the magnetic field typical 50/60Hz.  If the ground for the main AC power panel is bad, this may part of the problem.
Duke
 
So I just unplugged everything except the mic/mic preamp/mixer/headphone amp.  Plugging things in one at a time is revealing a lot.  Had an external hard drive causing noise.  It was located in another room...plugged it into another circuit and the noise disappeared.  I'll continue this approach.

As far as the power cabling, are you talking about mc cable... I'm currently using romex throughout.  I have the armored/mc cable feeding the sub-panel and romex going to the various outlets.  Not homeruns, just piggy-backed of the next outlet.  I could probably run one designated mc cable run to see if that helps out any. 

I might bring another feed from the main panel for a 'dirty' circuit for all my computer related stuff.

Any advice on what should have it's own designated circuit?  I currently have a circuit for my 2 inch tape machine, circuit for my analog gear (converters/preamps/compressors/etc...) and computer circuit.  There is also a lighting circuit.  Not sure what circuit my converters should reside...

Thanks again for the help here.

Nate
 
The noise/interference is more of  a buzzing noise.    Probably residing in the low to upper mid frequencies.  I don't think it's a 60 cycle hum...  I've got some gas and water piping in my garage that I could utilize.  I could run a ground wire and clamp to it.  I know the main panel is grounded plus a ground rod... 
 
How dry is the soil around the one? ground rod?

I'd never use any kind of water tube as an electrical ground. It's illegal over here, but it isn't wise. If, let's say a power amp develops a problem, it could kill someone in the kitchen or bathroom.

And I've even seen someone trying to ground to a PVC pipe...  :'(

And get that external drive's PSU fixed before it eats your data!
 
Grounds here are tied to both grounding rods and water mains from the street...  I'm not going to tie anything into the water or gas lines...if anything, I'd drive a new rod into the ground near my garage.  I'm going to rearrange my studio wiring first before I do anything with the grounding system at this point.

 
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