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How to trace blocking distortion with a scope

Discussion in 'Amp Tech Center' started by _Steve, Oct 16, 2020.

  1. _Steve

    _Steve TDPRI Member

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    It's a ClassicTone 40-18025 designed for 50W Marshall clones.

    Yeah NFB is fully disconnected at the moment while i debug so unfortunately not the cause. Off topic, but on my last build (a 6V6 from a Hammond organ) my "NFB" loop actually makes the amp looser and more distorted. I need to get back to that at some point to work out what im doing wrong :)
     
    dan40 likes this.
  2. andrewRneumann

    andrewRneumann Tele-Holic

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    Hi Steve. I’m curious where you are on this. And did this amp ever work the way you wanted it to?
     
  3. _Steve

    _Steve TDPRI Member

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    Hey Andrew,

    I put in a good couple of hours yesterday trying to identify it with the scope using various techniques and ideas but to no avail. So today I decided to take it off the bench and back upstairs to play with my guitar to see if the sound gave me any more clues or ideas to follow.

    Well... the bu-whah is no longer happening and as far as I can tell nothing at all has been changed on the amp.

    Its kinda frustrating because I like to tackle these problems and solve them so I learn something. I need to fix a few other things on it tomorrow so maybe it will re-appear. Then I have an EL84 build i really want to start on - I was never good at relationships! :)

    -Steve
     
  4. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Weird noise on loud notes, something changed when you picked up the amp and moved it -- I bet you've got a bad solder joint somewhere. ;)
     
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