Rob’s 5E3 mods

Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Nov 12, 2019.

  1. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I have made it back to my recent 5E3 build to do a few mods in an attempt to make the amp a bit more modern and versatile.

    https://www.tdpri.com/threads/ubuyguitars-5e3-project.944300/

    I have done the following mods;

    Larger first filter cap
    3-way negative feedback
    Lead channel
    Pre-PI master volume

    Following the directions fro RobRob’s site, the master volume is a 1M pot. I used the Standby switch hole and shielded wire tucked under the lip of the chassis. It is still very quiet. Here’s the wierdness... all the way down, I still get a pretty good signal. Starting to turn the pot up, there’s a very quick volume jump at about 20%, then it doesn’t get much louder after that (it’s loud, full volume). Is this normal for this mod?
     
  2. Pick_n_Strum

    Pick_n_Strum TDPRI Member

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    I'm probably the last person that should be answering this since I have very little experience, but, is it possible you used a linear taper pot instead of an audio taper pot?

    I'm going to add this to a build I'm currently working on and I have some questions for you since it sounds mostly successful - what shielded wire did you use?
     
    Last edited: Nov 12, 2019
  3. archetype

    archetype Fiend of Leo's

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    Could the pot have the rong taper?
     
  4. King Fan

    King Fan Friend of Leo's

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    Which Rob MV mod did you do? IIRC he uses a 1MA pot on both his pre-PI MV and his Type 3 post-PIMV.
     
  5. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Yes. It’s a 1MA pot. The shielded wire is triple strand with an outer shield I pulled out of an organ donor.
     
  6. muscmp

    muscmp Tele-Afflicted

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    my 5e3 build, without the mv mod, does that anyway. once you get to a certain point it doesn't get much louder.

    play music!
     
  7. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I had a similar issue with the master on my Spitfire build. That schematic also called for a 1MA pot. Out of curiosity, I put a meter on it and discovered that it went silent at ~475ohms. I replaced the 1MA with a 500KMA and now it performs exactly how I would expect to behave. That is a significantly different MV design though.

    The not going silent part has me suspecting builder error.
     
  8. D'tar

    D'tar Friend of Leo's

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    The PI tail, 56k keeps the signal from going to zero/ground. Assuming you have it wired in place of the 1M grid leak.
     
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  9. D'tar

    D'tar Friend of Leo's

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    I believe you may have it all correctly implemented. Its not going to work just like a volume pot and is more effective at reducing blocking distortion with the option to stay stock 5e3 at full up. Does the 5e3 have any volume pot that acts normal?:cool:There are some good tones in there but most of them are still pretty loud. This is just my experience with the Pre PIMV.
     
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  10. Paul G.

    Paul G. Friend of Leo's

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    Yes, the pre-PI master definitely lets a good amount of signal through at "0". The response is not terribly linear, but I wouldn't say it's unusable, I find it to give a reasonable response between 8:00 and 11:00. It works well enough so I don't feel the need to mess around with it.
     
  11. printer2

    printer2 Poster Extraordinaire

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    Check the pot with an ohm meter at 50%.
     
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  12. King Fan

    King Fan Friend of Leo's

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    And while you’re at it, measure grid to ground while you sweep the pot...
     
  13. printer2

    printer2 Poster Extraordinaire

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    Don't forget the lower lug of the pot is not at ground potential. For someone that wants the pot to work as a master volume all the way down, keep the 1M resistor at the grid and put an extra capacitor between the pot wiper and the grid. Then take the lower lug to actual ground. The pot will have no dc on it or be elevated in voltage. Only AC will go in and out of it and it will act normally.
     
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