Amp repair (GK MB Fusion) Los Angeles

Discussion in 'Amps and Cabs [BG]' started by SilkyStrings, Apr 13, 2012.

  1. SilkyStrings


    Aug 27, 2006
    Ok guys my almost new, (6 weeks old) MB fusion is making a noise. A whistling squeeling type type, not loud but gets louder the longer I play. I isolated it to the signal chain, it's definitely an internal fault with the amp. The vendor (Bass San Diego) sent me to GK, GK via email is recommending I take it to one of their service centers in Los Angeles area. :(

    I was hoping to switch it out for a new one seeing as it's so new but oh well.

    Can anyone recommend which service center to go to. I have no idea at this point who is good and who is not (they're all good right?) :help:



    SOLUTIONS Downtown Los Angeles

    AUDIO DESIGN & SERVICE North Hollywood

    Anyone have any experience with these guys before I flip the coin so to speak?

    I must say I'm bummed. I think that little head has a really great tone. I hope it's a quick and easy fix.

    Thanks for listening
  2. craig.p


    Sep 28, 2008
    New Hampshire
    Is that the one that uses three 12AX7 tubes? If so, swap the tubes around and see what happens. If things change for the better or worse, you might simply have a tube that's on its way out.
  3. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    it sounds like a super simple fix to me. it's probably just one of the 12AX7's that went microphonic, and i'm guessing that it's the first gain stage one that's closest to the input jack.
  4. Don't know the warranty period on the tubes but they may be covered still. [email protected] (artist relations) might be able to help with which repair shop seems best (if he can't arrange some other option).
  5. SilkyStrings


    Aug 27, 2006
    Yup, I was thinking microphonic tube too. I would fix it myself but, I don't want too void the warranty by opening it up. Besides I can't be 100% that's the fault. BTW I did get an email from Brian at GK, no specifics so I suppose if it's a tube then anyone can fix it. I am over thinking this as usual. (Took me 6 months to pick a new amp!)

    Thanks for the support bassists, I do appreciate your input. I'll will let you know what the outcome is.:bassist:
  6. username1


    Dec 28, 2005
    alberta canada
    I wouldnt try changing the tubes yourself in that amp. Let the warrantee depot do it. I changed the tubes in mine and it is no easy job. A small transformer has to be removed and a circuit board to allow clearance for the tube covers to come off. It might void your warantee if you do that yourself.
  7. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Washington, Utah
    John K Custom Basses
    wow! so much for tube rolling in that amp. :eek:
  8. Morning Beer

    Morning Beer

    Oct 2, 2009
    Definitely, I just opened mine up to pull a tube to try in a another amp. Once I had it opened I took one look and started putting it back together.
  9. SilkyStrings


    Aug 27, 2006
    I hope the tubes are covered, it's barely a month old!

    Thanks for the heads up on that, I woke up during the night and thought, I'll just change the tubes myself, but it's probably not a good idea. I don't want anyone to have a reason to deny warranty coverage on this amp.

    I checked the reviews this morning regarding repair shops around here, seems like everyone has mixed opinions, so I'm just going to take it to the closest place I think.

    Funny, my old Eden head never had any issues, bought it new in 1995, it has a tube too. I have heard GK is good quality too so I'm just unlucky.

    I'm debating if I should have gotten the MB800 instead, no tubes, more power. I did like the tone of the fusion better in the store though, it is much fatter sounding than I was expecting. It sounds sweeter IMHO than my Eden WT300, especially through the Eden Cabs (2x10T and 115T). Grindy but not harsh with crisp highs. Good useable tone for me i think.

    Maybe I'll call the store again and see if they will switch it out for a new one.
  10. New tube production is no where as good as the "old days". G-K does not make their own tubes, they buy from a supplier and test as best anyone can. :)
  11. SilkyStrings


    Aug 27, 2006

    Well, my MB Fusion is on it's way back to Bass San Diego for refund or replacement.

    I had it dropped off at Audio Repair Specialists in Canoga Park, Los Angeles for warranty repair, unfortunately they did not find a fault. I brought it home, and sure enough after a few minutes of playing the high pitched whine is back. Funnily enough if i touch the speaker cable jack housing the pitch of the whine/whistle changes, it also goes away when I engage the limiter button. The volume does not have to be up at all to hear it, it only needs to be plugged into a speaker. After experimenting with different cables again I am convinced the amp is defective.

    George at Bass San Diego is stepping up here to take care of me, so a big thanks to him for helping.

    I'm disappointed that ARS did not find a problem, it cost me a $25 bench fee to hear that the amp was OK.

    Naturally I could replace it with another MB Fusion, I can't help being a little leery about doing so.

    I may try something else. I play through an SVT and an 8X10 at rehearsal, which sounds and feels great (no surprise). George has suggested the Aguilar TH-500 as an alternative. I use either an Accugroove Tri-115 or an Eden 2x10T + 115 stack. Not sure what I'll do now, but at least my problem is solved and I feel better.
  12. IMHO I would give the MB Fusion another go! :D
  13. SilkyStrings


    Aug 27, 2006
    I'm debating it, it was a nice sound. :bassist:
  14. Stumbo

    Stumbo Guest

    Feb 11, 2008
    I would ask for a refund since they failed to find an existing problem and, since you're getting a replacement/refund on the amp, I'd use that as the basis for making the request. Whether GK or the repair center refunds the money, I'd pursue it because GK needs to uphold the quality of their outsourced repairs. I go to the top if no refund is forth coming.

    Something similar happened to me with a Honda van I had purchased new and was still under warranty. When I took it to the dealer, the service writer came up with a couple of items that he thought was causing the problem. I paid for the repairs and left. The problem returned and the source was traced to the alternator, a warranty item.

    After the repair was complete, I ask for a refund for the initial repairs that didn't solve the problem. My defense was that the Honda reps/service people are the experts and made the initial diagnosis, not me.

    It was nearly $200 involved in the refund so I didn't let it go. The begrudgingly refunded the money (I'm sure Honda Corp. yelled at a few people about the deal) because they could not refute my logic.

    Good luck.
  15. nostatic

    nostatic Supporting Member

    Jun 18, 2004
    central coast
    Endorsing Artist: FEA Labs
    That would be my pick. I had an MB Fusion and it is a nice amp, but was a little edgy for my taste. You can get plenty of grit from the TH, and you won't have to worry about microphonic tubes ;)
  16. SilkyStrings


    Aug 27, 2006

    The Vendor has the MB Fusion in question now and has confirmed that it is making a squealing sound. GK has requested that the amp be sent back to them for diagnosis. Once I find out their diagnosis I will attempt to get my money back from Audio Repair Specialists. It's not much but its the principal that counts IMO. I'm still amazed the tech couldn't duplicate the issue.

    In the meantime I have the option to get another amp, leaning toward the Aguilar today.

    Thanks to all who helped out here. The outcome of course is I know where I will not take my gear for repair in future. :spit:

    P.S. Just ordered a TH-500 from Bass San Diego
  17. Reviving an old thread... I'm having the exact same problem with my old MB Fusion 500 (I got it in 2011 I believe). A squealing noise, almost like a loud current noise... Goes away completely once the limiter is engaged... So I'm wondering, did you ever find out what the issue was?
  18. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Find a GK authorized service center, they should be able to sort it out for you.
    Stumbo likes this.