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GK 700RB-II hum problem (and solution)

Discussion in 'Amps [BG]' started by rhino72, Mar 15, 2014.


  1. rhino72

    rhino72

    Joined:
    Mar 5, 2014
    Location:
    Pagosa Springs, CO
    I've been lurking for a long while, and this is my first post.

    I recently bought a Gallien Kreuger 700RB-II, used, from Guitar Center, and had it shipped to me. I also bought a new GK Neo 112 from Musician's Friend.

    The cabinet arrived first, and I was excited to try it out when the head arrived a couple of days later. For the last few years I've been playing through an Ampeg 108 practice amp at home, and borrowing an amp from church when I needed to play out. My last 'real' amp was a Hartke 3500 and 410, that I sold around 1998.

    Anyhow, I got the amp, plugged everything up, and was greeted with a really bad buzz/hum. I tried switching between speakon and 1/4" speaker outputs, which didn't work. I tried gently wiggling the speaker cable, and the instrument cable, which didn't make it go away, but did make the hum change in volume, up and down, and sometimes go away. I also noticed that pressing down on the case made the hum change and sometimes go away.

    I purchased the Guitar Center extended warranty with the amp, and was preparing to take advantage of it, but being curious, frustrated and impatient, decided to open the case. I opened it, and plugged it back up, and it was dead silent, and sounded great with my Lakland. I unplugged it and reinstalled the case, and the hum was back, just as bad as before. I removed the case again, and again the hum disappeared. This time, I decided to reinstall the case lid with everything plugged in and the amp running. After installing 3 screws the hum came back, and would come and go when I moved/pressed on the case.

    At this point I happened to press against the 1/4" speaker jack on the back, and the hum changed and got worse. I checked the nut on this jack, and it was barely finger tight. I tightened it as much as I could by hand, and the hum went completely away. I tightened it some more with a wrench, and it has been perfect since. I assume that jack being loose caused some sort of ground problem. It's gone now, hopefully for good. If it stays nice for the next several days, I'll be gigging with it. It sounds great compared to the 200 watt Hartke 12" combo I've been borrowing.

    I thought I'd share this, in case anyone else is having this same problem. This (so far) saved me from the trouble of shipping the head to a repair center.
     
  2. Jim C

    Jim C

    Joined:
    Nov 29, 2008
    Welcome and great 1st post
     
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

    Joined:
    Aug 25, 2007
    Location:
    Toronto Ontario Canada
    Glad you sussed out your problem. :)
     
  4. wave rider

    wave rider Supporting Member

    Joined:
    Jan 5, 2005
    +1

    Thanks for adding another data point to the troubleshooting toolbox!

    =wr=
     
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