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Odd hum issue live

Discussion in 'Live Sound [BG]' started by I am Soma, Dec 9, 2013.

  1. I am Soma

    I am Soma Supporting Member

    Jan 2, 2013
    Good morning all,
    Not sure where to post this. My current rig is a Fender Dimension through effects to a my Fender 100T. Multiple shows/practices and I've had no issues. Played a show this past weekend at a nice venue and the minute I turned on my amp I was hearing a light hum/hiss. The plot thickened whenever I touched my knobs I would hear a light crackle. At one point I got too close to the Mic and got a nice little zap. The rig itself sounded fine but wasn't a fan of all the humming, hissing, and overall feeling like I was about to die via electricity.

    What was the issue and how do I avoid this in the future?

  2. fokof

    fokof One day ,I'll be in the future

    Mar 16, 2007
    Sounds like a grounding issue from the local AC.

    Try other AC circuits when that happens and check if PA & Stage share the same ground.
  3. I am Soma

    I am Soma Supporting Member

    Jan 2, 2013
    Thanks man! So if I have no idea what sharing the same ground means would I just talk to the soundman?
  4. It could be a faulty (missing) earth connection to the mains outlet.

    Is it ok now or still humming?
  5. I am Soma

    I am Soma Supporting Member

    Jan 2, 2013
    It was right back to normal when i got back to the practice space
  6. CAW


    Apr 18, 2010
    Sounds like incorrectly wired power at the venue, with missing ground as others have already suggested. That will cause all kinds of problems, and could potentially result in electrocution as well. Not safe at all...
  7. JohnMCA72


    Feb 4, 2009
    It means that the ground for the AC that your amp was plugged into was not at the same level as the AC that your PA was plugged into. Plug your amp into the same circuit as the PA. Back at your rehearsal space, your amp & PA grounds were good.

    "Ground" is not necessarily "ground". Among other things, ground is used as a reference level for electrical references of sound. An imbalance in grounds - one is at a higher voltage level than the other - causes current to flow along that ground path, which makes the hum.

    That "nice little zap" is not a trivial issue. Do not allow a condition like that go on, or somebody could get seriously hurt.
  8. I am Soma

    I am Soma Supporting Member

    Jan 2, 2013
    thanks again!
  9. Hi Dustin

    That's a grounding problem and it can be very dangerous. I highly recommend investing in an AC power outlet checker http://www.amazon.com/Electrical-Re...d=1386608205&sr=8-1&keywords=AC+outlet+tester and always test AC power outlets before use and don't use faulty AC outlets. Also, if and whenever you encounter faulty AC power grounding, hot mic's, etc - you really should/ need to refuse to work/perform under those dangerous conditions.

    EDIT: Due to danger - faulty AC power outlets at venues that aren't maintained up to code, really should/need be reported to authorities.
  10. +1000

    After getting a 240v (UK) mains shock to the mouth from a live mic while holding a grounded bass (no fun I can tell you) I am now ultra careful. We always have a mains checker plugged in and refuse to switch my amp on unless it says everything is good.
  11. derrico1

    derrico1 Supporting Member

    Apr 12, 2005
    Charlottesville, VA
    There's some peace of mind to be had if you have a wireless unit in your kit bag. Sometimes that gets around this kind of problem, by at least isolating your bass from the electrical system.

    Sure, the right solution is to insist on clean power or else walk. But some nights, a wireless is the practical difference between having a good gig or else having to cancel a show or suffer through a night full of buzzing DI and shocks from the vocal mic.
  12. I have a related question: Is there a device I could use to remove buzz from the electrical current? Story - we just played a local bar and when I turned by compressor pedal on, there was all kinds of buzzing. There were only 2 outlets for the band to use, and 1 had a couple extension jacks and a neon sign plugged into it. I was thinking that the power cord running with the neon sign might have been the culprit. As an IT guy, we use power conditioners for some laser printers. I was wondering if anyone had any experience using those in venues that may not have electric wiring up to par.
  13. If it was just your compressor that was picking up the interference from the neon sign then check that the case is grounded properly and all you leads (cords) are in good condition, check with a multimeter that they haven't gone high resistance.

    There is also a chance that the "designer" didn't take into account the fact that you need to limit the bandwidth of audio circuits to that which is audible and useful. It wouldn't be the first time that some amp or pedal has picked up a radio transmission and output it as audio (demodulated it). This is totally avoidable with good circuit design.