Plexi bright cap

Discussion in 'The Workbench' started by Marcomel79, Sep 20, 2021.

  1. Marcomel79

    Marcomel79 Well-Known Member

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    Hi everyone, i built an 18 watts plexi clone from tube town that sounds absolutely killer. Using only the high input on the bright channel without bridging the channels, the amp is very bright even with the treble completely turned down. I use the mids on 10 btw... the bright cap right now is 4.7nf, not sure if thats standard, and i just ordered a 2.2nf from russia, some obscure NOS stash.... anyway, is there any point in trying with a 3.3nf cap or the 2.2nf is enough to cut down the brightness of the amp?
     
  2. AlvisX

    AlvisX Garage Guerrilla Gold Supporting Member

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    Try some alligator clips across the pot and try various cap values until you find the one that suits your ears
     
  3. PelliX

    PelliX Well-Known Member

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    They should make a difference, yes. Whether it cuts it for you - that you must judge :)

    Also, don't get NOS caps - there is no NOS factor for caps. You wouldn't go out of your way to get a 1960's battery or fuse for something, after all.
     
    Last edited: Sep 20, 2021
  4. gregr

    gregr Well-Known Member

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    How bright do you want it is the usual answer, but there’s another/complimentary way to help you decide before reaching for the iron a second or third time.

    What value you choose also has a lot to do with how high you want to set your gain control. The higher you set the control the larger the cap needs to be if you want it to do anything.

    Don’t waste your money on NOS caps.
     
    Last edited: Sep 20, 2021
  5. Marcomel79

    Marcomel79 Well-Known Member

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    It was more like the cheapest option... didnt wanna pay 15$ for shipping for just one item.... here in norway its incredibly difficult to find particular cap values....
     
  6. ToneWitch

    ToneWitch Well-Known Member

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    Better yet, use no bright cap at all. :jam:
     
  7. Marcomel79

    Marcomel79 Well-Known Member

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    I play mostly ac/dc, airbourne type stuff, so not very much gain...
     
  8. Marcomel79

    Marcomel79 Well-Known Member

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    Ive seen videos of johan segeborn playing with no bright cap and the amp loses its edge IMO
     
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  9. ToneWitch

    ToneWitch Well-Known Member

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    I prefer no bright caps myself. Sounds much smoother and no shrill ice picky. Definitely give it a shot if you haven’t.
     
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  10. gregr

    gregr Well-Known Member

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    No cap is too warm for humbuckers. For me 220pF is a bit more sensible. Depending on how aggressive you like it, 1nF is a good value without going over the top.
     
    Last edited: Sep 21, 2021
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  11. Marcomel79

    Marcomel79 Well-Known Member

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    I like it roaring!
     
  12. Marcomel79

    Marcomel79 Well-Known Member

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    I will!! Gonna take it off before trying another value anyway!
     
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  13. neikeel

    neikeel Well-Known Member

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    Depends on where you have your volume pot. Over 8/10 it is 'not there' and between 0 and 5 it has most effect. Really big caps (4n7) are full bandwidth bypass so are more a gain boost then bright cap. That is more the 100pF-500pF range.
     
  14. PelliX

    PelliX Well-Known Member

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    This ^. To bypass the cap you can just clip from one leg to the other.
     
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  15. Marcomel79

    Marcomel79 Well-Known Member

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    Usually i have it around 4/5... it gets too gainy after that...
     
    Last edited: Sep 20, 2021
  16. Marcomel79

    Marcomel79 Well-Known Member

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    Im not sure i understand... im still learning....
     
  17. johan.b

    johan.b Well-Known Member

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    When marshall values don't work for you, fall back to "what would Leo do? "... fender bright cap was usually 120pF... I'd go 120-470pF to start with
    J
     
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  18. Marcomel79

    Marcomel79 Well-Known Member

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    thank you everyone for your input. Really appeciated!
     
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  19. gregr

    gregr Well-Known Member

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    Please let us know what you end up using.
     
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  20. yladrd61

    yladrd61 Well-Known Member

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    I like 100pf on Ch I & 500pf on Ch II, shared cathode with single coils, may need to go higher with, split cathode and/or humm bukkas.
     
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