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GK Fusion 800 - dead

Discussion in 'Amps and Cabs [BG]' started by MD-BassPlayer, Aug 12, 2020.


  1. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    Well, not completely dead, it powers up and has had very little play time. We're talking single digit hours in total, but it hasn't been played for possibly two years. I broke it out today to A/B with my other amps to see if what I like is really still what I like. The bass and cab line up has changed. I plugged it in and powered up, had a very brief decaying note at low volume. Now everything is powered up, light are on, but I'm not getting any sound on either channel A or B. If I engage the mute switch there is a small click through the speaker, so I think the power amp is working. made sure all the ribbon connectors were connected and those look ok. I'm thinking the preamp tubes at this point. Maybe swap them out one by one? I think I have a 12AX7 somewhere. These were brand new quality tubes, but tubes do go bad.
     
  2. Contact GK.
     
  3. cableguy

    cableguy Supporting Member

    Jun 4, 2009
    North Bend, WA
    Try plugging in to the effects return. See if you get volume there. Your master volume would control it from the effects return.
     
    BasturdBlaster and fast slapper like this.
  4. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    They kinda sucked the last time I contacted them. Honestly, I'll probably trash this amp if it's anything more than tubes.I had to send it in before to fix a random white noise issue, so it's hitting the point of not reliable enough to take to a gig and not reliable enough to sell.
     
    BrentSimons likes this.
  5. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    That's never bad advice, but it would also be a good idea to check all the outputs, including FX send for output, and send signal to all the inputs, including FX return.
     
  6. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    Good tip. I should have thought to try that. Thx! I get sound through the effects return, so I'm hoping just a bad tube.
     
  7. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    DI out doesn't work in PRE or POST positions, still trying to find the extra tube but I did find a few pedals that I forgot that I owned.

    EDIT: looking at the schematic, even the Pre signal path hits a tube if I'm reading it correctly. Visually the tubes look fine.
     
    Last edited: Aug 12, 2020
  8. cableguy

    cableguy Supporting Member

    Jun 4, 2009
    North Bend, WA
    Try to reseat the tubes to see if that changes anything. Definitely do not trash the amp over a bad preamp section. If the power section works well, it should be worth fixing. Otherwise, plenty of people like me get their tone from a pedal board straight in to the effects return anyway. Using a micro amp as just a power amp.
     
  9. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    I reseated the tubes and they are glowing, so it looks like the tubes are ok. Put the tubes in different positions so that even if one is bad, I should still get something through the DI. Older GK stuff has been rock solid, but this amp couldn't have been babied more and it's been trouble. I was going to sell it earlier because it came back form GK with a clean bill of health, but I'm glad it didn't sell. Are the Legacy amps any better?
     
  10. JimChjones

    JimChjones

    Aug 6, 2017
    SE England
    It could, of course, very easily be a bad input jack socket. Do you get anything out of the tuner out?
     
  11. Wasnex

    Wasnex

    Dec 25, 2011
    I don't have a schematic but the block diagram from the owners manual shows the signal hits V1A before going to the pre DI. The post DI is taken at Effect Send.

    Just because the tube heaters are lighting up does not mean all of the tubes are passing signal. If the pre DI is not getting signal, V1A is suspect.

    If you don't have a spare tube to roll through the amp. Try pulling V2 and putting it in the V1 position. Then see if the pre DI signal is passing.

    Is the Mute switch functioning normally. Should turn red when engaged.

    The only other thing I would suggest is maxing out Gain A, Gain B, Master A, Master B and toggling the A/B switch a few times. Also try with the footswitch if you have one.
     
  12. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    Nothing form the tuner out, but the way it died I don't think it was the jack there was a very brief (half second) of signal getting through and then nothing. So, I think it's component level and since everything is mounted to a board, if it's not a loose connection or a bad tube, it's going to be a board replacement of some sort.
     
  13. Wasnex

    Wasnex

    Dec 25, 2011
    Tuner out on this amp is the same as the Effect Send per the block diagram in the manual.
     
  14. cableguy

    cableguy Supporting Member

    Jun 4, 2009
    North Bend, WA
    Sorry to hear about your troubles. I bought mine used here on TB and it's been rock solid. My only issue ever was solved by spraying de-oxit on a couple knobs to get rid of some scratchy pots. My previous 700RB-II I had to send back to GK at one point. They did a great job fixing it and it was rock solid until I sold it.
     
  15. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    I think I've tried each of the three tubes in each position, no luck on anything from Effect Send / DI Pre or Post and the Tuner out. The mute is working as designed, turns red when engaged and it does a great job muting, heh. I tried cycling A/B but no luck there either. Well, at least it didn't let the smoke out. There is a nearby service center but I really don't want to spend much on an amp that I've put probably under 10, definitely under 20 hours on and it's died twice during that time.
     
  16. Wasnex

    Wasnex

    Dec 25, 2011
    If you have one bad tube the signal will not make it's way to the Effect Send, Tuner Out, or Post DI. If the circuit is intact, a good tube in V1 should get the signal to the Pre DI. The Mute switch mutes all outgoing signals, but the Effects Return will still send a signal to the Power Amp.

    Hook up a speaker. Is there any noticeable change in the level of circuit noise when you max out the various controls? I believe the Masters are working since they are after Effects Return; crank these all the way up. Then look at the block diagram and note where the tone controls are located in the circuit. For example, the Bass and Treble controls are on the last tube section. So if you crank up these controls and get more circuit noise, it tells you that tube section is working. The next tube section is associated with the low mids, and the next tube section is the high mids, etc.

    It does sound like the amp may be a lemon. Sorry you have had a bad experience. If the amp is ganked and you don't want to deal with it, I suggest donating the amp instead of throwing it away. If the power amp works, someone can use it. Someone may also be interested in having it repaired.
     
    cableguy likes this.
  17. Ryno1330

    Ryno1330 Supporting Member

    Jan 14, 2020
    It's not my intention to turn this into a bash fest but I really wanted to buy a Fusion S when they came out. I started doing research because I can't try prior and there were a lot of reliability issues that scared me off - sorry you seem to be one of them.
     
  18. MD-BassPlayer

    MD-BassPlayer Supporting Member

    Jun 19, 2003
    I'm basically $900 or so into this amp, do I want to spend likely $200 more to fix it? I think it's time to cut my losses. I have other gear that's reliable. If I plug into my Mesa Subway head, my first thought would be that my cable died or the battery in my bass is dead. I have a GK RB 400-IV or whatever the nomenclature is in the practice space and that has been rock solid. GK's Class D stuff, not so sure I'd recommend them. It's like a voodoo doll amp.
     
  19. Kukulkan61

    Kukulkan61 Supporting Member

    Feb 8, 2011
    Northern Arizona
    If GK sent it back to you with a clean bill of health and you didn’t use it anytime after that it’s on them, contact them..
     
    mikewalker likes this.
  20. Ryno1330

    Ryno1330 Supporting Member

    Jan 14, 2020
    Probably not. I went with a Bergantino Forte HP and couldn't be happier. Reliability and customer service go a long way for me.
     
    MD-BassPlayer likes this.

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