Gallien Krueger Fusion 550 pop issue

Discussion in 'Amps and Cabs [BG]' started by John Lovell, Jun 20, 2020.

  1. John Lovell

    John Lovell

    Jun 20, 2020
    Hi guys, I have a GK Fusion 550 that has a minor issue. At switch on there is a huge "rifle shot" pop through the speakers. With all controls to zero and standby on, the sound still occurs.

    I took it to a local tech who replaced a number of possible suspect components such as thermistors and capacitors but not able to fix the problem. There appears to be a DC voltage applied to the speakers to cause a very loud "crack" on startup.

    Anyone have the same issue and if so, how was it fixed?
  2. BassmanPaul

    BassmanPaul Inactive

    Welcome to talk bass John where men are men and sheep are nervous! :)

    Many amps have a switch on and/or a switch off 'pop'. I would suggest that you contact GK for their advice if this issue is troubling you.

    How old is the amplifier?
    madjazzbass and wave rider like this.
  3. Mine does that too. More like a low frequency thump though.
    madjazzbass likes this.
  4. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado
    Same here. Mine is more a low volume "thump" once the amp fully cycles on power-up. The one suggestion I have is, you could mute the amp and then turn on the power. That might solve the issue, it might not.

    I believe this amp is still featured on GK's current model's page. Wouldn't hurt to reach out to them for advice.

    EDIT: You can try replacing the speaker cables and trying a different cab to see if it makes a difference.
  5. madjazzbass

    madjazzbass Supporting Member

    Jan 5, 2014
    Thankfully I've never had that issue with mine; that sounds like a problem to me. Is everything grounded?
  6. Wasnex


    Dec 25, 2011
    Many solid state amps have an automatic mute. When the amp is turned on, the circuit applies a mute to the input of the power amp, until it stabilizes. The mute is also applied instantaneously when the amp is turned off until the power supply has a change to bleed down a bit.

    Here's and example of the circuit from a GK RB series amp.

    The "Fault" tab on the right monitors voltage in the power amp. The "GRN POWER ON" and "RED PROTECT" leads at the bottom drive green and red status LEDs on the front panel. On the left side, the "MUTE1" tab energizes a Mute circuit on the Power Amp module, which generates "MUTE2" for the tweeter amp.

    My QSC PL236 amps have a similar circuit but it seems to be way more complicated.

    The problem could also be unrelated to muting.
  7. BassmanPaul

    BassmanPaul Inactive

    Most power on mutes just disconnect the speaker load until the amplifier is stable. You can hear the relay click in after a few seconds. On power off the relay just drops out again instantly disconnecting the load.
  8. John Lovell

    John Lovell

    Jun 20, 2020
    2014 model.
  9. John Lovell

    John Lovell

    Jun 20, 2020
    This is a very loud rifle shot. I have had the amp since new from 2014 and it has just started with the loud pop.
  10. BassmanPaul

    BassmanPaul Inactive

    If you have a multimeter measure the voltage across the speaker jack without a cabinet connected. It should read zero volts or very close to it.
  11. agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Probably best to contact GK's customer service.
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  12. BassmanPaul

    BassmanPaul Inactive

    There's that too! LOL
  13. Podo


    Mar 24, 2012
    I just bought a Fusion 550 secondhand and have discovered it does the same thing. Its a very loud POP a few seconds after powerup.

    It also does it when powering down, but not as loud
  14. John Lovell

    John Lovell

    Jun 20, 2020
    I am going to send it to the local Aus repair centre soon to get it fixed soon. I have purchased a new GK MB500 lightweight D Class amp, nowhere near the quality for the fusion, but sounds good and portable. I will post the outcome of the repairs in due course.
    Wasnex likes this.
  15. John Lovell

    John Lovell

    Jun 20, 2020
    Just to fill you in, I sent the unit to the GK service centre in Melbourne during Covid and it took a while for it to be repaired.
    It turned out to be a faulty Power Amp module and the PCB assembly was replaced and cured the problem.
    Not too expensive for the repair and good communication with the service centre.
    Wasnex, agedhorse and Katoosie like this.