Sunday, 14 February 2010

JFET Buffer

16 comments:

  1. Hey, do you know if this buffer works?

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  2. Hi

    Well it's pretty much a generic common drain amplifier. I did that layout a while ago and have had a look to see if I saved the exact schematic I used (I usually keep them in a "done" folder where I store my layouts) but I can't find it for reference. Looking at some other buffers though, the layout seems to line up, but some use a 10uF instead of the 100nF output capacitor so if you're having issues that is the only significant difference. Check out the transistor buffer on the Beavis site:

    http://www.beavisaudio.com/techpages/Buffers/

    Apart from that, are you sure you're using a JFET with the correct pinouts?

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  3. I will be building this tomorrow. I ordered the parts thursday nite so when I get all the parts in(should be Monday), I'll let you know if I got it. I ordered everything on the diagram above. I will also tell you if it works!

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  4. So i built the buffer just like the layout above. The results were that I lost a small bit of high end. Not very noticeable, but in the end, I felt like i had lost the piercing shimmer of my Gretsch Penguin.

    I guess you can say it works but, You cant say that because its not really doing its job in keeping the pure tone.

    Am I right on this? Or will I never find a buffer that doesnt take away from my signal even just a little?

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  5. Did you try it with the 10uF or 100nF output capacitor?

    At the end of the day all a buffer does is convert a high impedance signal to low impedance which helps with losses caused by long runs of cables, multiple short patch leads etc. I'm sure with some guitar/effect/amp combinations buffering your signal just doesn't sound quite as good as when it's unbuffered and this may just be one of those cases.

    It may be worth trying a generic opamp buffer layout like this one:

    http://i76.photobucket.com/albums/j6/IvIark_2006/Layouts/Vero/ICBuffer.png

    or the Klon buffer I just posted on the blog, just to see how you feel your gear responds to them.

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  6. I just used the 100nF cap. I suppose I could try a 10uF. Would that reduce "resistance" in the signal? I am also going to have a couple guitarists put this on their boards. Im going to see if they think they lose anything by having it.

    I just am running 25ft mogami cable from guitar to board(board runs through 5 pedals) then another 25ft mogami to my amp. So if anything, I guess I expected to have more highs in my signal... or is that not supposed to happen after going LowZ

    also, what type of IC should go in that first buffer? perhaps a TL072?

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  7. hey, would this work to balance the impedance mismatch between a piezo pickup with a magnetic one do you think?

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  8. Damn you. I was going to take this one down next.. :) Well. I think i can call it a day..
    +m

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    Replies
    1. Ha ha, sorry mate, I found someone who built it on FSB

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  9. Hello, what is the purpose of the 100R input resistor? The Beavis Jfet buffer does not use one... Also what happened with the discussion about the output capacitor? should I try the 100n or the 10u?

    best

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  10. Hello, what is the purpose of the 100R input resistor? The Beavis Jfet buffer does not use one... Also what happened with the discussion about the output capacitor? should I try the 100n or the 10u?

    best

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    Replies
    1. It's a current limiting resistor. Some people like to included them, others aren't bothered but it can help with switch popping

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    2. but if you intend to leave the buffer on all the time, instead of turning it on and off, would it be ok to remove it?

      thanks

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  11. I ran out of mpf102 and 2n5457, so I used a j201, would that be ok or this one will give me higher output impedance?

    thanks

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    Replies
    1. also I removed the 100R and 1M resistors (I assume that the last one is a pull-down resistor right?)

      thanks

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