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Ampeg SVT CL - Power Fault on Specific Bass

Discussion in 'Amps and Cabs [BG]' started by Thing1, May 14, 2021.

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  1. May 14, 2021 #1
    Thing1

    Thing1

    Feb 24, 2014
    Hey guys, I have hauled this amp to my amp tech twice and spent $200 but have had no luck. I have a 2005 Ampeg SVT CL that is doing the power fault led flash when using my Mark Hoppus bass through it while driving the amp hard. This ONLY happens when driving the amp hard with that specific bass (around gain 4, master 7). The amp makes a poof sound and fades away then the power led starts flashing. If I use my Ibanez bass everything works just fine.

    My amp tech has resaugthered the board and biased the amp. I think the Mark Hoppus bass is driving the amp too hard with the Seymour Duncan Quarter Pound pickups.

    Any experts know what might be going on? Is it just a situation where I can roll the bias back a little bit on the back of the amp? I've had this amp for a few months and really want to enjoy it, it's been in the shop for 3/4 of the time.
     
  2. May 14, 2021 #2
    agedhorse

    agedhorse Supporting Member Commercial User

    Feb 12, 2006
    Davis, CA (USA)
    Development Engineer-Mesa Boogie, Development Engineer-Genzler (pedals), Product Support-Genz Benz
    Can you try the same bass on another amp of the same model?

    Are you sure your amp is set to the correct impedance?

    Are you sure your cabinet is correctly labeled with regards to impedance? Nobody made changes?
     
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  3. May 14, 2021 #3
    seamonkey

    seamonkey

    Aug 6, 2004
    Wasnex likes this.
  4. May 14, 2021 #4
    Wasnex

    Wasnex

    Dec 25, 2011

    AFAIK the fault kicks in under two situations: 1. the line AC voltage is too high, 2. one or more output tubes are pulling dangerous levels of current.

    Although conceivably the amp may only shut down with a particular bass, IMHO the problem is still with the amp or output tubes.

    Here is a more in-depth post I wrote on how the bias sense and fault circuits works: Svt cl fault
     
  5. May 14, 2021 #5
    beans-on-toast

    beans-on-toast

    Aug 7, 2008
    Did you try reproducing the fault at the tech’s shop? Low power line voltage can cause this. Take a reading of the AC wall voltage where this occurs. If it’s below 115VAC it can cause this.

    Don’t run the amp through a power conditioner.

    There are many possibilities. Hopefully the tech checked the power tube cathode resistors.
     
  6. May 14, 2021 #6
    seamonkey

    seamonkey

    Aug 6, 2004
    IK Multimedia - AmpliTube SVX

    "So accurate, it even shut down
    Funny story… during the first phase of testing with the original engineers, one particular software model was being driven so hard that it "shut down." Completely stopped working. But the lead engineer approved the model on the spot. You see, there was a slight design flaw in the actual amplifier that would cause a power fault shutdown if the amp was driven too hard for too long. The software model was so accurate that it even replicated this design flaw! "

    Find tech and that know of the design published in the schematic:
    Ampeg SVT-CL | Repair