Vox AC15CC Muddy Bass

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by dbun, Jul 8, 2008.

  1. dbun

    dbun Member

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    Hi Guys,

    The sound on my AC15CC changed suddenly during a gig. All through practice and the first song it sounded great, as soon as we hit the second song things were different.

    Whenever I picked a note, especially the lower strings EAD, the bass would ring out uncontrollably, as if the amp had lost all its definition and control. The sound had become mushy and instead of being tight and focused, sounded all muddy and lacked clarity.

    Does this sound like bad tubes? I have since replaced the preamp tubes with new ones and it didn't make much of a difference. The only ones left are the power tubes.
     
  2. PlumBob

    PlumBob Member

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    Sounds like feedback maybe. Was the second song a good bit louder than the practice/first song level? Have you tried to reproduce the offending sound?
     
  3. dbun

    dbun Member

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    Nah...all the volumes remained the same. I was using the same effects and everything as before.

    It seems to be always like this now, sometime worse, but it's not like how it used to be.

    Is it possible that as the power tubes wear they bias hotter??
     
  4. phsyconoodler

    phsyconoodler Member

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    As tubes get tired they get muddy sounding.Rarely does the bias get 'hotter',especially since the AC15 is cathode biased and as the tube gets weaker it draws less current.The number one problem in a tube amp is the tubes.Easy to change and if the sound comes back to where it was before,you've nailed it.
     
  5. mcdes

    mcdes Member of no importance

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    sounds like tubes to me too.

    another silly thing, but does happen, check all pedals/amp for anything outa place, ie, eq, someone may have bumped or turned a knob, it happens.
     
  6. dbun

    dbun Member

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    tried a fresh pair of JJ power tubes...seems like the problem is fixed!! Bass is a lot 'tighter', 'controlled' and 'punchy' and all the other frequencies are equally present too.

    I had noticed that the higher strings, especially the high E string, was sounding very 'weak' compared to others, but thought maybe the strings on my guitar were due for a change.

    I guess it does pay to have a known good set of tubes as a 'reference' and chuck them in every now and then to see if the amp sounds any better or not.

    Thanks for the help guys
     

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