Mod Gone Wrong?

Discussion in 'The Workbench' started by Neddi, Jun 16, 2019.

  1. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Or he only read the first post and then commented after which never reading any of the subsequent post.
     
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  2. stringer

    stringer Member

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    From one David to another Well done.
    I jist might need to seen one of my stock build to ya to mod.
    David Stringer
    Ps. ROLL TIDE ROLL
     
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  3. NewReligion

    NewReligion Well-Known Member VIP Member

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    Thank you.

    If you ever have interest just PM (Start a Conversation it is called here) me.

    David Hopkins...♫
     
  4. Fender

    Fender Active Member

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    If I may, I'd like to ask a related question : I have a 2204 build with a loop which which runs very well IMO except that if i set it to high input, hi gain (above 6/7 on the high input), i get a very high whistle which disappears if i play something on the guitar (temporarily, it gets back if i stop playing the guitar) or turn the loop off (bypass). What can cause this type of oscillation and is the solution simply to shield the loop board from the gain circuit or it's more complicated that that ?
     
  5. Scott Johnston

    Scott Johnston New Member

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    I highly doubt 2 boards are bad. They seem simple enough, not much to go wrong. I think your "installer" botched it. Make him pay for his crappy work.

    This is the mod board you are talking about, correct?

    https://store.metropoulos.net/collections/amp-mods
     
    Last edited: Aug 2, 2019
  6. mickeydg5

    mickeydg5 Well-Known Member VIP Member

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    Scott, finish reading the thread.

    I hit the first page or spot read before and it always bites me in the ass. :D
     
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  7. NewReligion

    NewReligion Well-Known Member VIP Member

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    Hello Fender. You may consider starting a new thread for this topic which will yield better results. Try #2 First.

    1.) Q: What type of loop is it. Passive? Or buffered by tube or otherwise?

    1.) A: I have had issues with some mods when using a Metropoulos Zero Loss Loop too close in proximity to the input grids of the first stages of 12AX7.

    Without drilling new holes try relocating the send/return to a different position (I use cork coasters to lay Loop boards on to insulate from grounding while testing.

    2.) Q: Did you use high gain components to bias your 12AX7’s? That is to say low cathodes &/or high anode/plate values?

    2.) A: Microphonic's can be tamed if not eliminated by using an input capacitor. Try a .68uf from the hi gain input grounded jack tip to the ground location on your closest potentiometer being the gain most likely.

    If this works you can try reducing the cap value to a .047uf & hopefully this will work.

    For reference .68uf is what Friedman uses. .047uf is what Cameron prefers.

    Good luck I look forward to hearing back. I suspect the loop board proximity layout but of course I am guessing as I don’t know the circuit.

    David Hopkins
     
    Last edited: Aug 3, 2019
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  8. Fender

    Fender Active Member

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