Amp losing clarity after a few minutes of hard playing

Discussion in 'Amps and Cabs [BG]' started by Gabu, Mar 11, 2002.

  1. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    Does anyone experience where the amp sounds nice and clear... for a while. And as you dig in it gradually begins to sound a bit fuzzy to you?

    It's kind of slight... I kid of wonder if I am just playing too damn loud and wrecking my ears.

    But I swear, it loses something after a while. :confused:
  2. Either, but more solid-state related: the final bias is shifting the output stage into a non-linear state. Hard playing is heating things up good and if the "trans-diode" (solid state) in the power stage bias circuit isn't correctly compensating for this warm-up, it can shift the stage into class "B" or even further - into class "C" .

    Tube: besides the bias issue, your bottles may no longer be matched anymore and one side is hogging current. Could also be a wonky cathode-bias resistor if it's a low powered amp.

  3. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    Thanks for your reply. The amp in question is a solid state power amp with a tube preamp. Is there some way to test if these components your are decribing are not working properly? Should I just take it to an amp shop?
  4. Gabu


    Jan 2, 2001
    Lake Elsinore, CA
    Hmm... I am not sure. My impression is that it does, but I would have to confirm.
  5. Matthias


    May 30, 2000
    Vienna, Austria
    Interesting. I experienced exactly the same with my Hartke 2000.
    Now I use a head with twice the power and it is much better. But I still have the feeling the sound is slightly degrading when playing on higher volumes for a while.

    My guess always was that the 'behaviour' of the circuitry changes somehow with high temperature just like Scorpio said.

    BTW I don't mind a little distortion at high volumes, but it is annoying when it won't go away when I play softer again.

    Interesting enough this is hardly an issue with my Gallien-Krueger MB150 which I sometimes push so hard that you can fry eggs on the heat-sink. (;) well not really, but it gets more than just warm)
  6. I seem to get this with my monoblock II I think I get quieter and more distorted after a while. It makes me think my bass batteries are dying
  7. Hey Gabu,

    Unfortunately that isn't something that can't be properly diagnosed and repaired without an accurate volt/ammeter to check quiescent (idling) current of your output transistors, and an oscilloscope and signal generator, to properly bias the amp for maximum linearity at high/low volumes after the repair is made.

    Unless you or a bud have those toys :) and diagnosed the problem before, I suggest taking it to a competent repairshop.

    Good luck Dude! :D
  8. Matthias


    May 30, 2000
    Vienna, Austria
    Is this a question of repair at all?
    I mean is this a fault of the amp which can be repaired or is it inherent the design?

  9. More probably a bias-alignment problem. I can't see any Mfr. purposely designing inconsistent distortion into an amp. It would either be there or not - but not ONLY after things heat up.
  10. I've noticed the exact opposite with my amp. I'm using a Hartke 350-watt head, and it's been frustrating the hell out of me every practice. I can't seem to get any kind of decent sound at first, but after about a half hour or so, it starts sounding good. Then again, it might be my ears too.
  11. Matthias


    May 30, 2000
    Vienna, Austria
    I thought this phenomenon occurs at the limit of the amps capability, when it is (slowely but surely) 'running out of steam'. Of cause no mfr. would purposely design it this way.

    Like if the engine of your car is overheating it does not necessarily mean that there is a fault in the cooling system - maybe you just been asking too much of it...

  12. craigb

    craigb G&L churnmeister Supporting Member

    I know I get lots of "ear effects" on my sound. I've noticed that when the band is playing "louder than usual" my perception of my sound is all over the place. What starts out as a good, clear sound seems to become muffled. I usually attribute it to my ears being overloaded. I've got earplugs but keep forgetting to try them out.

    I'm not sure how to verify if it's the amp or your ears, can you try a different amp (borrow one?) once and see if you notice the same thing?
  13. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    South Shore MA
    It's the ears. The low end is the first thing to get attenuated by the auditory system and you end up hearing more of the mids which on their own tend to sound a bit fuzzy comapred to the fundamentals.

    I've had this happen to me with every amp I own, under certain (loud) conditions.
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