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Anyone have an issue with a GK MB800 shocking you?

Discussion in 'Amps [BG]' started by Jarrett, Dec 30, 2012.

  1. Jarrett

    Jarrett Supporting Member

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    I had a weird thing happen last night at a gig. First of all, I was using a questionable cab that was part of the back line. About 45 minutes into playing the soundguy told me he was getting a buzz from my DI out from my GK MB800. So I shook the cable a little and made sure it was seated well and the amp powered off. So reseated the power cable to make sure it wasn't loose and the power came back on, same buzz.

    So the soundguy started to run a 1/4" inch from my line out to a direct box and once he plugged one end into the line out and touched the other end, it shocked him. So we unplugged the cable. I then laid my arm across my strings and they shocked me. At that point I unplugged everything and had to run the rest of the night with no amp, just through DI.

    Has anyone heard of this before? I couldn't figure out if it was an amp issue or a cab issue or what. Any info greatly appreciated.
  2. RickenBoogie

    RickenBoogie

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    Well, it's a grounding issue, and most likely the amp. I'd take it in to a qualified tech for a looksie.
  3. JustDavid

    JustDavid

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    A questionable cab as part of the supplied backline has me wonder if the electrical outlets are wired correctly. Did your outlet test OK?
  4. Jarrett

    Jarrett Supporting Member

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    It was a strip with two other things in it and they were fine.
  5. 2milehighspike

    2milehighspike Supporting Member

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    Have you plugged into you're own cabs yet to see if it is ok? I had a similiar thing happen with my old Ashdown head in a room that has horrible wiring. I don't want to start the power conditioner debate again , but when I used it after that incident in the same room it did'nt happen again and have used it ever since with my MB800.
  6. Jarrett

    Jarrett Supporting Member

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    I haven't yet, but going to. Little nervous to be honest :)

    So you had a MB800 shock you as well? Did you start a thread about it? If so, I'd like to read it.
  7. tmdazed

    tmdazed

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    Mains out of phase could be a possability , we had a line 6 that used to shock the guitar player , simply moving to a different outlet seemed to work. Could be a bad earth for the place you were plugged into as well
  8. Jim C

    Jim C Supporting Member

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    Can't see how a cabinet could cause a shock
    The DI into the amp could easily cause a shock situation with faulty wiring
    If the DI was completely unplugged, see no reason why an amp that didn't provide a shock 1 minute earlier would do so now other than being damaged by a ground loop (never seen this but suppose is possible).
    At home, plug in amp, hook up bass, volume down, turn power on, use a voltmeter (on AC scale) to measure any voltage between the strings and a known good ground (water pipe, third pin of an AC outlet, etc)
    Then repeat this measurement and measure the amp case instead of the bass strings to ground.

    Edit: Today might be a good day to head to Home Depot and buy one of those plug in the wall, LED testers that will alert you to an open ground or reversed L1 to Neutral phase issue. About $10.
  9. Eric Moesle

    Eric Moesle Supporting Member

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    i once had my gear fry at an outdoor show the very minute they plugged the xlr connector into the DI. It turned out the power line my bass rig was plugged into had the hot and ground reversed, which by itself wasn't a problem - my rig worked fine by itself - until it was connected to the PA thru the DI since the PA power line was wired correctly. The two didn't mix. The instant they connected, the magic smoke was released. DI was fried, as was my Eden preamp.

    After that, I always use a cheapie A/C line tester before plugging in.

    Oh, and my Furman power "conditioner" didn't do a damn thing to help, warn, or protect....
  10. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

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    My guess would be a bad ground at the outlet in the venue.
  11. rapidfirerob

    rapidfirerob Fusion rules! Supporting Member

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    I had a big party for my 50th BD and hired a mobile recording guy. While we had no problems on stage (rented a church basement), the recording person melted some of his gear. I felt really bad, but thankfully he was fully insured.
  12. Jarrett

    Jarrett Supporting Member

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    I just fired up the amp at home with my cab. No issues. Played a while, then plugged in an XLR to my DAW preamp and no issue. Amp is working fine. No shocky at home.

    By the way, I have used the amp at the gig several times in the past. Same amp, same cables, same old beat up cab. Just this time it delivered a shock.

    Does that give any clues?
  13. DWBass

    DWBass The Funkfather Supporting Member

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    Ungrounded outlet at venue which is quite common! Depending on the year the venue was built (all buildings built after 1966 must have grounded outlets) , this could be a code violation!! I personally do not plug in any venue with ungrounded outlets! I don't play with my life (or equipment) like that!
  14. christw

    christw Always searching for the right Ric... Supporting Member

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    This. I always bring an outlet tester with me to gigs for that reason.
  15. B-string

    B-string Supporting Member

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    Venue's handyman "repaired" some wiring since you played there before. Failed ground on the strip outlet you plugged into.
  16. fdeck

    fdeck Supporting Member

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    What else was plugged into the outlet strip? Tube guitar amp?
  17. tmdazed

    tmdazed

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    yup outlet out of phase
  18. 1958Bassman

    1958Bassman

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    If anyone wants to test the wiring, get a test light with incandescent bulb. Attach the clip to one chassis and touch the tip to the other chassis- if it lights up at all, you have current flowing between them If it's bright, don't even think about touching one with one hand and putting another part of your body in contact with the other chassis. It's not a matter of a little voltage leak but if you have actual current flowing, look out! The LED-type test light is useless for this.
  19. delta7fred

    delta7fred

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    +1

    It sounds like a badly grounded mains outlet or faulty power strip or kettle lead, assuming you amp is ok. There is no way a cab could cause you to get a shock.

    We have an outlet tester permanently plugged into one of our power strips, they cost next to nothing. If I don't get the all clear from it I don't plug in. I go through all our power strips and kettle leads on a regular basis and replace any that are not 100%.

    I've had 240V shock from a mic (this is the reason I am so fussy about the integrity of the mains wiring and power strips). I was playing a grounded bass at the time, it felt like I had been kicked in the teeth by a donkey.

    The ground wire had broken in the mains outlet (in a dodgy rehearsal room) and was touching the live terminal so the PA amp chassis was at 240VAC. Ouch.
  20. Mystic Michael

    Mystic Michael Hip No Ties Supporting Member

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    Absolutely. I'm shocked, yes shocked I am, that so much power can come from such a little box... :D

    MM

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