Plexi Micro Build

Discussion in 'Shock Brother's DIY Amps' started by Bitsleftover, Feb 27, 2020.

  1. Bitsleftover

    Bitsleftover Tele-Meister

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    I’ve finally begun my next project.
    I want to build a low power living room amp which encapsulates the vibe of the early “Plexi” era “4 hole” Marshalls before they moved into the cascaded gain direction of the metal face 2203 etc.


    I’m going to base the PI and power section very closely on Robrob’s Bassman Micro LTP while incorporating several of the mods he lists on his site and borrowing some things from elsewhere.

    I’m hoping with the addition of a few rear panel toggle switches I’ll be able to follow the main developments from Fender Bassman through JTM45 and Bluesbreaker 1962 to the mighty 1959 Super Lead Plexi.

    The only thing I intend to change about the power section is the addition of a Solid State Rectifier switch to give tube rectification like the Bluesbreaker and Diodes like the JTM and all that followed.

    Starting at the front of the preamp, I will add the standard 4 input jacks.

    V1 will have a toggle to chose between shared cathode 820r-330uf bypass and split V1B 2k7 0.68uf)

    I may add a switchable bright cap to V1A Volume pot to give a JTM Bright/Normal option.

    The bright (SLP) channel will have the cap installed and I will experiment with 0.022 vs 0.0022 coupling caps. I suspect 0.0022 may be too thin through a 1x10 combo.

    V2A will have a switchable cathode .68 bypass cap as per later SLPs.

    The tone stack will be switchable from the JTM 56k 220p arrangement to the SLP 33k 470p setup.

    I’ll add a 3 position negative feedback switch to give progressively less feedback.

    Just for an added challenge, I intend to add a MOSFET driven tremolo to the normal (JTM Bluesbreaker) channel, with a switch to totally remove it from the circuit when disarmed.

    Most of the above can be added after getting stock Bassman Micro LTP up and running, but I will make provisions on my board and chassis for my mods to be added later on one by one.

    I don’t care how long or how much trial and error it takes. It’s a learning experiment and a project I’ll enjoy.

    Thumbs up for adventure!

    (And standby for lots of questions!!!!)



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  2. Bitsleftover

    Bitsleftover Tele-Meister

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    Starting with a cab to put it in.
    I”m reusing the cab from my previous failed Marshall class 5 project.
    The control panel cutout isn’t big enough to I stripped the tolex, enlarged the cutout and roundovered the edges.
    The adhesive was a nightmare to remove, so I emailed customer support at Marshall for advice and they replied within 20 minutes! Don’t use solvents, use heat” was the advice. So an hour or so with a heat gun and it was gone!
    I always thought the class 5 would have benefitted cosmetically from the gold string on the top and bottom panels. So I took the opportunity to route an 1/8” groove and recovered it all with fresh tolex.


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  3. Bitsleftover

    Bitsleftover Tele-Meister

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    [​IMG]


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  4. Bitsleftover

    Bitsleftover Tele-Meister

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  5. Bitsleftover

    Bitsleftover Tele-Meister

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  6. Bitsleftover

    Bitsleftover Tele-Meister

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  7. Bitsleftover

    Bitsleftover Tele-Meister

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  8. Bitsleftover

    Bitsleftover Tele-Meister

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  9. Bitsleftover

    Bitsleftover Tele-Meister

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    Chassis next


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  10. Bitsleftover

    Bitsleftover Tele-Meister

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  11. Bitsleftover

    Bitsleftover Tele-Meister

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    Times up. Off to work away for a week.



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  12. dan40

    dan40 Tele-Afflicted

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    Nice work! I recently built the micro JCM 800 from Rob's sight and it really does sound great. Good luck with your build!
     
  13. Bitsleftover

    Bitsleftover Tele-Meister

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    Thanks Dan


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  14. Bitsleftover

    Bitsleftover Tele-Meister

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  15. Bitsleftover

    Bitsleftover Tele-Meister

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  16. Bitsleftover

    Bitsleftover Tele-Meister

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  17. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Very nice work.
     
  18. Bitsleftover

    Bitsleftover Tele-Meister

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    Thank you


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  19. Bitsleftover

    Bitsleftover Tele-Meister

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  20. Bitsleftover

    Bitsleftover Tele-Meister

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    470pf treble peaker and a few resistors missing.


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