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loud hum issue

Discussion in 'Amps and Cabs [BG]' started by mattbass6945, Jan 23, 2014.

  1. i apologize if this has been covered numerous times. i have a history of not being able to use the talkbass search function effectively.

    my amp seems to have a loud hum that goes away only when i hit the mute button on the amp. since it doesn't happen anywhere else, i believe it to be the outlet i'm plugged into at practice.

    is there anyway to put something between the plug and outlet to eliminate this? i always assumed electricity was delivered by magical fairies and it scares me. i am no electrician, please use laymen's terms!:smug:

    mods, please move this if it is in the wrong forum.
  2. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Is the hum there when your bass isn't plugged in to the amp?
  3. i haven't checked that, but nothing changes when i touch the bridge or strings, or mute from volume pedal or tuner.
  4. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    What make and model is the amp?

    Are the nuts tight on your input jacks? You want tight nuts to ensure a good contact.

    Plug your instrument cable into the amp and touch the tip of other end of the cable. Is this the sort of hum that you are hearing?

    If no, is the hum 60Hz or 120Hz? Compare it to a reference tone of these frequencies that you can find on the internet.
  5. it is a genz gbe 600. all nuts/jacks are tight. we practice at our singer's shop. he's a mechanic and it's an old building, so since it is only noticeable there, i assumed it was the power source (plug). does this sound reasonable or remotely accurate? i know there's probably other things to check first, but i won't be back at practice until monday. may have to take a little checklist with me and diagnose then!
  6. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Yes it can be the location. The additional info helps. Since it only happens at the garage, it sounds like there is an external source of noise at the garage that is getting into the input of the amp. Fluorescent lighting, a light dimmer, a motor or fridge, bad electrical wiring, a bad transformer out in the street, a cell phone too close to the amp, and a long list of other things can cause this.

    Why it is only your amp is the question. First try a different instrument cable. Then try moving the amp and if possible, put it on a different electrical circuit.
  7. i don't know for certain it's only my amp. i just think i'm the one who is most particular about that sort of thing. i wouldn't doubt if lighting were the problem. there's an 8,000 sq ft shop with fluorescent lights. if moving it to a different location/outlet doesn't help, is there anything (product) i can put between the amp and outlet to eliminate the issue?

    thanks for the help thus far. i appreciate your time!
  8. 1958Bassman


    Oct 20, 2007
    Get one of these, to test the outlets-


    Don't spend that much- they can be found for a lot less, but get one that looks like it. If you get the one with a button on top, you'll be able to test GFCI outlets, too.

    Old buildings, especially when they're industrial, are notorious for electrical problems. Measure the line voltage, too- if the fuse/breaker panel has problems, e.g., loose screws on the terminals inside, the voltage can be wrong- if the neutral lifts, you'll launch anything designed for 120VAC that's powered up. If you find wiring problems with that tested, just plugging something between the amp and outlet won't help- it needs to be repaired properly.
  9. awesome.

    i have to assume that the audible hum is a warning that there is an issue. is it safe to continue running my amp on a faulty plug? any long term effects? i understand that this is a vague question seeing as how we haven't actually determined the issue at hand, but it does make me curious.
  10. Fluorescent lights can cause havoc with less than well shielded bass electrics. If you unplug the input cable you can narrow it all down by half.
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    With any complex problem you have to break it down and look at one thing at a time to determine what the issue is. Start with the easy things first, one at a time, and see what happens.

    Try a different instrument cable. If that doesn't resolve the issue, kill all the lights. Next try plugging the amp into a different circuit (on a different circuit breaker).

    If the wiring is faulty, drawing a lot of current by the band instruments could cause a fire. If there is a wiring issue, an electrician will need to look at it to resolve it. If you have an AM radio that can be manually tuned between stations, it can be sometimes used to detect issues with the wiring. Walk around with the radio and hold it near 120VAC wiring runs, junction boxes, panels, etc and see if you get a lot of noise at a particular location. This noise could be getting picked up by your amp. The radio detector can help determine where the problem is.

    If the problem is caused by fluorescent lighting, there could be a bad ballast that needs replacing. The noise could simply be coming from the lighting. Not much that you can do.

    Will the noise hurt the amp? Probably not. Without looking at it in person, it is hard to be sure.
  12. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    If the noise goes away with the mute switch, it should also go away when the master volume control turned down.

    Unplug the instrument cable from the bass, if the noise goes away, it's entering through the bass electronics or an unshielded cable.
  13. very cool. i'll try the basics first at next practice. couldn't hurt to pick up one of those gfci testers either, they look cheap and simple enough to use. thanks guys!
  14. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa, Product Support-Genz Benz
    A true gfci tester is only useful for testing gfci protected receptacles. A standard receptacle tester is going to be a better tool for testing hour power source.
  15. good to know! this is all so foreign to me, much appreciated!
  16. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I have outlet testers that I bought from Home Depot that can test both regular and GFI outlets. A handy tool, especially given the cost.

    I never plug an amp in without first testing the outlet and measuring the line voltage with a voltmeter.
  17. for someone who really can't afford to be replacing amps at the moment, this sems like a good tool to have around. i'll look into it. thanks again, guys!