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Old April 15th, 2019, 10:22 PM
Hordriss Hordriss is offline
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Electrical hum with recording gear

This may possibly be more of a question for an audio type place, but I've previously found the people here to be very helpful so here goes!

I have a HP Pavilion 15-p245sa laptop, running Windows 10 (Intel Core i3-5010U, 8GB RAM). It's my only computer so I use it for everything (browsing, light gaming etc), but especially music recording as I'm a hobbyist singer/songwriter.

I record by plugging my instruments and microphone into a Behringer U-Phoria UMC22 USB audio interface. The mic is a Behringer C1 condenser mic, and with it being a condenser, requires 48v phantom power which is what the interface provides.

A couple of weeks ago, with nothing obvious happening to cause it, I suddenly started getting an electrical hum from the mic channel with the phantom power activated (and the mic can't be operated without it).

I'd originally assumed either one of the cables or the interface would be the issue, as I've read that the circuits can go bad in USB interfaces after a while.

However, having plugged the gear into another laptop, I did not get the same hum which now makes it seem pretty much certain that my laptop is the cause of the issue.

It happens regardless of whether the laptop is running on mains power or battery, however the hum is considerably louder when on mains.

Here is a link to the humming sound, as it is via mains power.

https://drive.google.com/file/d/1V5n...ew?usp=sharing

If anybody can suggest what is the exact cause of the issue and if/how it could be resolved I'd be eternally grateful as I can't afford to buy a new laptop at this point in time!

EDIT: It seems to be location related, as having tried it into my laptop again but in a different room I'm not getting the buzz so this suggests some kind of electrical interference from another device. I'll have to do some further digging and figure out the cause!

Last edited by Hordriss; April 15th, 2019 at 10:38 PM.
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  #2  
Old April 15th, 2019, 11:03 PM
Hordriss Hordriss is offline
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Ok, no worries. With a little bit of experimentation I've managed to get to the bottom of the issue.

Mods, please close!
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  #3  
Old April 16th, 2019, 12:08 AM
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IPR512 IPR512 is offline
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Just curious, can you tell us what the problem was?
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  #4  
Old April 16th, 2019, 12:44 AM
Hordriss Hordriss is offline
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Indeed. It was all down to my mic stand!!

Essentially, it's a tripod base, with the actual stand running through it and held by a clamp. The stand has fallen down and was touching the floor. I know there's parts of the electrical system under my bedroom floor so this must have completed some kind of circuit, thus creating the electrical hum (one downside of living in a house which is around 130 years old lol).

I only realised it must be something other than the laptop when I brought another one up and tested it but still got the hum. I then took my laptop and the gear downstairs and tested it (minus the mic stand). I initially thought one of my other electrical devices must be causing interference.
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  #5  
Old April 16th, 2019, 12:30 PM
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IPR512 IPR512 is offline
Jill
 
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Good for you for using your head to figure it out. It sure beats using your feet to run out to buy a new laptop.
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  #6  
Old April 16th, 2019, 12:34 PM
Hordriss Hordriss is offline
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Quote:
Originally Posted by IPR512 View Post
Good for you for using your head to figure it out. It sure beats using your feet to run out to buy a new laptop.
Indeed!

It was probably dumb luck as much as anything, but a new computer was out of the question at this time in any case. And it would have been galling to buy one and found out that wasn't actually the issue!
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  #7  
Old April 16th, 2019, 04:48 PM
Ensign Tzap Ensign Tzap is offline
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Nice finding the cause.


EMI problems or RFI issues can be tough to solve sometimes.
{The Audio File you posted is a definite 60Hz Hum.}

Am I wrong in guessing the Mic stand is metal?

If you know anything about AC Transformers.
They have a primary coil, a steel Core, and a secondary coil, or coils.

Basically the Mic stand was acting as a Core between the AC Power lines in the floor, and the wire to the Microphone.


Signed: Ensign Tzap
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Old April 16th, 2019, 05:03 PM
Hordriss Hordriss is offline
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Quote:
Originally Posted by Ensign Tzap View Post
Nice finding the cause.


EMI problems or RFI issues can be tough to solve sometimes.
{The Audio File you posted is a definite 60Hz Hum.}

Am I wrong in guessing the Mic stand is metal?

If you know anything about AC Transformers.
They have a primary coil, a steel Core, and a secondary coil, or coils.

Basically the Mic stand was acting as a Core between the AC Power lines in the floor, and the wire to the Microphone.


Signed: Ensign Tzap
Thanks for the info.

And you are correct - the mic stand is almost entirely metal, aside from some the boom adjustment being plastic and the tripod feet having rubber feet on the end.
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