What makes mics hum-sensitive?

Discussion in 'Microphones (live or studio)' started by John Stafford, Jul 9, 2005.

  1. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Hi all,
    I was wondering what makes a mic hum when I approach the swtiches, and pick up low level background hum that no other mics do.

    I've been able to rule out ground loops, and I am using very well shielded cable. The body is screwed together very tighly, so there's no problem there.

    Oh yeah, the mic also needs to be grounded to stop the hum getting very bad.

    John Stafford
  2. Jp22

    Jp22 Guest

    I used to have a problem similar to this and it drove me absolutely berzerk! Turns out it was the computer monitor I was using. After I bought an LCD all the buzz and noise ended completely. Is your monitor a CRT by chance? :roll: CRT monitors interfere insanely with cabling and signals, especially if your monitor is near your computer :!:

    ~ Jp, "The Box" studio, Minnesota, US
  3. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Thanks JP
    In my case it happens even when everything else in the room is turned off and plugged out. I've tried everything I could think of.

    Today I'll try it on the open air and see if that makes any difference, although at this stage I don't expect too much :cry:

  4. anonymous

    anonymous Guests

    Feb 10, 2001
    Good luck on that one. Stuff like that can drive you nuts. :x
    Wish I had something more useful to say.
    Please let us know what it was once you figure it out.
    Good luck
  5. TeddyG

    TeddyG Well-Known Member

    Jan 20, 2005
    Shooting in the dark, here:

    Just one mic does this?

    What mic?

    Some mics have a procedure to change what pin does what - mostly for high/low impedence, I believe. Is this possible in this case?(Incorrectly wired for the cable/rest of the system.).

    Cables I've used - no matter their quality - sometimes DO have the pins wired "differently" than I expect. I hear that some countries use a different wiring plan for "balanced", for instance? Correct! Just different...

    Hate to go too far with this, but is it a "cheap" mic??? Or an exotic, vintage(Old), mic?

    Of course, the mic may have a genuine physical problem? Broken connection/ cracked board, etc?

    And, have you looked over the mic makers web site for instructions, specific to this mic(Like: If used around X$@%CX, it will hum!).

    Have you e-mailed tech support for suggestions?

  6. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Thanks for the input guys!

    There's actually two mics. One is an AKG C34 (forgot about that one!) and the other is a U87Ai. I have never had a problem with any Audio Technica or Rode mics (or even Behringer for that matter).

    I use an Apogee Mini-Me but have since tried the mics on a few other preamps. Neumann suggested better cables, and changing the wiring at the XLRs, so I bought Gotham cable and there was a difference. They told me that they couldn't imagine anything that would go wrong with the mic to cause this problem. If I run an earth from the Mini-Me, the mains hum disappears, but there is still sensitivity to touch as well as a very deep pulsating hum that I attributed to a storage heater, but now that it's turned off for the summer I'm still getting weird noises.

    This is such a pain!

    Thanks again

    PS None of my other mics pick up any hum, even if I don't attach an external earth to the the Mini-Me.
  7. bslotte

    bslotte Guest

    I tried two pairs of AKG C480B with CK61, CK62 etc. capsules once, and they were acting like really good antennas. They picked up everything including interference from my CD player several metres away (and they weren't broken - all 4 acted the same way and they were new).

    I wonder if the AKG's you mention have a similar "built-in" problem.
  8. vividsonics

    vividsonics Guest

    I had a client that bought a couple of U87's for their production studio at a radio station. Those suckers picked up WAY more RF (radio interference) than their Rode, Sennheiser and Shure mics. It might be possible that you're picking up some sort of intense RF that's affecting the mics. I've never found a good solution that cures this problem. I noticed on your avatar that you're from Dublin. Large cities tend to have a lot more RF problems than rural and suburban areas. Some one with experience in eliminating RF want to jump in here?
  9. Ivan158

    Ivan158 Guest

    i read in a book that attaching a ferrite ring to the ground wire in the mic cable will stop rf interference.

    my 2 centz
  10. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Thank you gentlemen, and sorry for not acknowledging you assistance earlier.

    The ferrite ring idea is interesting. I've heard of something like this before, but I didn't pay much attention to it as I wasn't having any noise problems at the time.

    Not only do I live in a city, but live on the same road as a large children's hospital, very near to a maternity hosptial, and about five minutes away from another hospital which is HUGE. I've often wondered if their equipment such as MRI machines cause contamination. There is certainly some very strange source of EMI around here.

    That's interesting about your AKGs. I remember reading about someone having a similar problem with a TLM-103. It worked perfectly everywhere else, but he got a replacement and had the same problem. He never had a problem with any other mic. There was a telephone switching box in his garden, so he balmed that, but I don't think he ever got the problem truly sorted.

    Thanks everyone!

  11. TornadoTed

    TornadoTed Guest

    I had this problem with my AKG Solidtube but that turned out to be a fault in the wall socket that I plugged the power supply into. I didn't think about it and always plugged into the same socket when recording. I know that's of little use to you, but I can empathise with your problem because it drove me crazy as I tried everything except plugging it across the room in another socket !!.
  12. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Hi Ted
    I wouldn't be at all surprised if there is something up with the wiring of the house. I've tried earthing the mics directly into the ground, and it seems to improve, although the electro-magnetic enviroment is probably different outdoors anyway, so it's difficult to make any sort of informed assessment :-?

    I still have a few tricks to try out before I take a flame-thrower to my gear. That would very quickly stop any hum problems :wink:

  13. Derm

    Derm Guest

    Hi John,
    Cant help with the hum but you've got to be on Temple Street, right?
  14. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Hey Derm, HOWYA YOUNGFLA!!!

    I actually live off the Crumlin Road near Our Lady's, so I'm also near the Coombe. James's is further away, but then it's pretty vast.

  15. Derm

    Derm Guest

    Doh! Our Lady's was my next guess.
  16. OJG

    OJG Guest


    You may well have solved your problem by now.
    Just in case you didn't;
    Try disconnecting every electrical appliance in your studio (actually pull the AC plug out).
    If that does not reveal the cause to the hum - try turning off all the lights in the room.
    I used to have a hum when talking on the phone and it took me a while to figure out that it came from the desk lamp.

    It is transformers that usually generate a hum.

  17. dpd

    dpd Active Member

    Sep 29, 2004
    yup - some mics respond to AC magnetic fields. CRT monitors are big-time offenders. Some mics (e.g. EV RE-27) aren't susceptible to magnetic noise. Others are quite so.
  18. roguescout

    roguescout Guest

    You are all wrong!

    The problem is hummingbirds!

    I put up a feeder outside my studio window and it was HUM HUM HUM ALL DAY LONG!!!

    Luckily though, I have a 30-06 M1 Garand rifle that is PERFECT for hummingbirds. So whenever the little buggers come around they get a little taste of HOT LEAD!

    My neighbors keep telling me to just take the feeder down... But where is the fun in that?!?!

    I know you are in Ireland, so maybe some vintage Enfield gear would work for you!

    Cheers! (y)
  19. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    Thank you gentlemen. I apologise for not responding sooner, but because I'm not very bright I didn't notice that there were more posts on the thread.

    I think there's a ground loop caused by my USB interface being grounded through my computer. When I plug the PSU for an AT4060 things seem to improve, but not always :-?

    I still have to look for other variables, but looking at the lighting situation is a good idea, so thanks for that :D

  20. John Stafford

    John Stafford Well-Known Member

    Oct 1, 2004
    I'm afraid using the Enfield carries a seven year prison sentence over here:cry: Even the cops are banned from carrying guns. I wonder if the humming birds would torment me from outside my prison cell :wink:

    Seriously though, the only time I heard a humming bird was in California (Palo Alto). I thought it was really cool -I wonder what it would sound like through a Marshall stack :lol:


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