Plexi bright cap

Marcomel79

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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?
 

PelliX

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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.
 
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gregr

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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.
 
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Marcomel79

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They should make 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.
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....
 

Marcomel79

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

gregr

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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.
 
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Marcomel79

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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, 1.5n is a good value without going over the top.
I like it roaring!
 

neikeel

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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.
 

PelliX

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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

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

Marcomel79

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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.
Usually i have it around 4/5... it gets too gainy after that...
 
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