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Possible power line / voltage issue (GK MB800)

Discussion in 'Amps and Cabs [BG]' started by Dr3thepooner, Feb 27, 2014.

  1. I had posted similar topic in live sound, just hoping more people will see it here.

    I have been having issue with my set up (GKMB800 + GKNeo4x10) in only one place - our jam space.

    We rent a pretty tiny room - 1bass /1guitar/ drums /vocals.

    I started to notice my sound volume would all of a sudden degrade and become way lower, and even distorted at certain times. The issue would go away on its own.
    That got me really concerned i might have a blown speaker, or damaged amp.
    But anywhere else i play it sounds just fine! I brought my setup to the music store, where i got it, and they tested it whole day and never saw an issue.

    What i realized later, my problem would start - almost at the same time the super loud metal band would go full blast next door... And i am plugged in likely to the same grid they are...
    I think requirements are 120v @ 15amp that should give me 1800Watt more than enough.
    This idea with power grid issue came in mind after i read GK manual where they mention, not to have anything with a lot of power draw plugged in the same grid.

    Any one here experienced issues with lower volume .. all of a sudden distortion / break up related to not enough juice / power / volts in the power grid???
  2. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    That's exactly what happens when the line power sags. Low enough line power lowers the voltages inside the amp. This lowers the voltage in the power supply. It translates into loss of headroom and distortion. It also affects the bias of the power section of your amp. This applies to both tube and solid state amps.

    Some amps are designed to perform better than others when presented with low line voltages. On the back of your amp it says 100-120VAC 50/60Hz. Although your amp can perform with 100VAC, it may not sound the same as at 120VAC. Lower than 100VAC, all bets are off.

    It would be interesting to take of volt meter with you to practice and measure the line voltage when both bands are cranking.
  3. Update

    Unfortunately, after all, this was a failing amp.
    The issue started to present itself more and more often, then i was able to reproduce it at home.
    Brought it back to L&M, its going out for repairs now.

    Now funny enough - they didn't have MB800 to lend me as a loaner, and gave me MB500 to play a gig with, which is fair enough.

    As soon as we started sound check - i found the MB500's DI was cutting in and out, which we replaced by sound guy's DI Box (ground switch was enabled).
    Then during the second song, it shut itself DOWN and then slowly turn on! ... with Gain at 12' and Master at 11' what? I do run VT bass in front but still, it was pretty quiet.

    Had to enable limiter, and turn down gain quite a bit (10') and was able to finish the gig that way... so far I really love the GK tone, but all this....

    Wonder if its my ****** luck, or I shall start looking for different brand.
    When i brought the MB500 back to the store , the rep looked and me like i was destroying them on purpose.
  4. Doug Parent

    Doug Parent Gold Supporting Member

    May 31, 2004
    San Diego, Ca.
    Dealer Nordstrand Pickups.
    I had that same issue TWICE with a MB800.
  5. BigEarl

    BigEarl Supporting Member

    Sep 29, 2003
    Austin, TX
    I am having this same problem with my MB800 right now. I'm taking it into the local authorized repair shop (Guitar Resurrection in Austin) tomorrow. Same symptoms!
  6. Sid Fang

    Sid Fang Reformed Fusion Player Supporting Member

    Jun 12, 2008
    Have you cleaned your switching jacks (FX return, headphones) or at least patched a cable from FX out to FX in? Crud there can cause drop-outs and distortion somewhat like what was described.