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Amp ground problems?

Discussion in 'Amps and Cabs [BG]' started by Jake Kinsch, Feb 4, 2016.

  1. Jake Kinsch

    Jake Kinsch

    Jun 9, 2015
    I have some 60 cycle hum when I play in a certain building. I go to the local college in my town to participate in their jazz workshop, but whenever I go there I always get a 60 cycle hum coming through the amp. But whenever I plug in my bass somewhere else through a different amp, there are no problems. I double-checked the wiring, and everything is done correctly, I even took the time to shield the cavities. The two amps that we switch back and forth on both have the same problem. There is a Gallien-Krueger MicroBass 1x12 combo, and a Markbass little mark III through a 1x12 cabinet. I've tried pressing the ground lift button on the back of the Markbass, but it doesn't do anything. I'm running a standard jazz bass. I'm assuming that the outlet that we plug into might have the ground disconnected or something like that.

    Does anybody know what might cause this/know how to fix this?

    Any help would be great!
  2. Some places just have noisy electric, for any number of reasons (lighting, motors, dimmers, etc.). We have a very popular mid-sized venue here in the St. Louis area which has notoriously bad power. You can try using a ground lift, and maybe switch the polarity of the power. Maybe run an extension cord from a different outlet on a different circuit. Sometimes, though, there's just nothing you can do except suffer through it.
  3. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    If you can take the amp to another location where it isn't making noise, then chances are an external influence is overwhelming the amp's shielding and is being picked up. It seems like this is the case here. Sometimes the amp can be better shielded using a sheet of aluminum or metal tape. There also can be an issue with the building wiring. An electrician can be called in to check it out. They should be told that amps are picking up more line level noise than they should be. There could be a fault in a junction behind the wall or at a lighting fixture. Fluorescent lighting can be a problem. There are other influences as was mentioned. Find an old AM radio that can be manually tuned. Tune between stations. Move it around the room, next to lighting fixtures, wall plugs. Any source of RF noise will manifest itself as loud static. It can help identify problem areas.

    If it happens all the time, it could be a bad ground. This can be due to oxidization at the input jack, or somewhere else within the amp. If the amp is older, it could mean that the power supply electrolytic capacitors need to be replaced. Line level hum is common when this happens.
  4. Jake Kinsch

    Jake Kinsch

    Jun 9, 2015
    It was fixed when I showed up today, so problem solved
  5. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    It also could be a bad ground in the building's wiring. It happens all the time in older structures.

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