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Ampeg SVT-4 Pro 'always-on'-Humm in the preamp-section (NOT DI)

Discussion in 'Amps and Cabs [BG]' started by PA-Trick, Apr 12, 2017.

  1. PA-Trick


    Jan 14, 2017
    Hi all,
    welcome to my first thread :D

    My Ampeg SVT-4 Pro (about 10 years old) humms continuously, no matter the pre/master-volume or if there's a bass plugged in.
    It stops if I go directly into the Poweramp!
    (If only 1 cab is connected the right power amp has to be plugged-into to stop the humm of course)

    I have only found one old thread, possibly about this:
    Constant Ampeg SVT-4 Pro Hum. Any Ideas?
    where @Basslan had a similar problem, but the thread stops, before he tested circumventing the poweramp.

    I probably won't fix it myself, but I'd like to narrow down the problem as much as I can, before getting the amp to a local tech here in Austria.

    Thanks for your help
  2. BasturdBlaster


    Feb 19, 2012
    Crandon WI
    Maybe run some DeOxit in the effects loops and the pre/power loops? Maybe a preamp tube going bad? Sorry, that's all I got:)
    PA-Trick likes this.
  3. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    I'd say a preamp tube would be the first place to look.
    PA-Trick likes this.
  4. PA-Trick


    Jan 14, 2017
    Thank you, that's probably the easiest to start.
    I somehow dismissed the idea, because the pre-volume doesn't change the humm at all.
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