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I recently purchased a Devine BM 400 Condenser Mic, but when plugging it in (XLR -> Audio Interface -> USB) I get a hum at around 50Hz, and some more peaks at 155, 2670, 365, and so on, with smaller peaks in between.

I already tried to: Change USB Cables from audio interface to laptop, playing from other speakers, taking out laptop power cable. Taking laptop somewhere else (same building), returning the mic and get a new one. But no results. Touching the mic or placing it elsewhere doesn't change anything, not even slightly.

I was hoping someone could help me based on the frequency spectrum.

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  • PS The mic is powered by my audio interface +48V, Audio interface is powered by my Laptop's USB Port, and the laptop is powered through either battery or net power, which is grounded.
    – Robert Broersma
    Aug 14, 2015 at 11:14
  • I would doubt any laptop is grounded, even if it has a 3-pin plug. Almost all small electronics are double-insulated rather than grounded. Tried another interface? What is it, btw?
    – Tetsujin
    Aug 14, 2015 at 11:31
  • Hey thx for the response. I'm not really much of an expert on electronics, I meant that the power outlet is grounded! Haven't tried another interface, don't have one unfortunately, the one I use is an ESIO MARA22XTU. You think it could be because I use a laptop? If so is there something I can do about it?
    – Robert Broersma
    Aug 14, 2015 at 11:39
  • It's very difficult to troubleshoot your setup without the ability to swap out parts for know good ones, such as the mic, the XLR cable, interface etc. At what preamp gains can do you get the noise? What happens if you record without anything plugged into the interface? It cannot be a ground loop since you're powering everything from the computer.
    – Johannes
    Dec 21, 2015 at 16:02

3 Answers 3

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1) - Make sure everything is plugged in to the same circuit. You can get a 60-cycle hum from having amps on one circuit and the board on another.

2) - Does the interface have an option for DC power from a transformer? Is so, you may want to get one and use it. Make sure the polarity is correct (TRS).

3) - Sometimes an interface will have a ground screw on the back. You might want to use a small wire to attach this to a grounded component.

4) - Check the ground on your power with an outlet tester (cheap at a hardware store). I've had setups with no ground onstage and literally had to run a wire to a pipe or a metal stake in the ground.

Good luck!

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Hum at 50Hz sounds very much like it is coming from the mains power. Assuming you are living somewhere on the planet with 50Hz mains power? Harmonics of mains power hum would expected to be at regular intervals (100Hz, 150Hz, 200Hz, 250Hz, 800Hz, etc.)

Laptop computers are NOTORIOUS for ground loop and similar problems with getting audio into and out of them. The very first experiment would be to operate the computer on batteries and completely disconnect the external mains power "brick" completely at both ends.

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  • Appreciate your time, but if you read my question you'd know that I already tried that.
    – Robert Broersma
    Nov 17, 2016 at 14:36
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    Did you actually unplug the power supply from the wall also? Your narrative was rather casual. If you are still hearing noise with just the mic, the interface and the computer, then likely the mic and/or the interface are broken. My first suspect would be the mic and/or the mic cable. If you unplug the cable from the mic end and wrap it with kitchen foil (to completely shield it), do you still get hum?
    – Richard Crowley
    Nov 17, 2016 at 15:59
  • I've received a replacement from the store I got the mic, and I still get the hum. So likely my audio interface is "broken" ?
    – Robert Broersma
    Nov 17, 2016 at 21:08
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    Then you have found that the problem is either the mic cable or the microphone. I will ask you for the SECOND TIME, to do the test with just the mic cable plugged in BUT NOT THE MICROPHONE. Do you understand how to do basic troubleshooting steps?
    – Richard Crowley
    Nov 18, 2016 at 16:45
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    I truly appreciate your time to help me with an unresolved hardware issue I had 1,5 years ago. However I do not appreciate your attitude. No, there is no hum when it is just the cable BUT NOT THE MICROPHONE. I will tell you for the SECOND TIME that I received a replacement from the store, wouldn't it be very unlikely that I receive two faulty items?
    – Robert Broersma
    Nov 19, 2016 at 13:22
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Just as another possible check: for a quick test ruling out the cable, you can plug the microphone directly into the sound card since an XLR cable connection is gender-neutral. Depending on weight of the microphone and orientation of the sound card, you'll need to prop up the microphone and it's likely to pick up any noise from the table (like hard disk noise if that's where your laptop is), so having known good cables to try beats this test, but just saying.

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