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Tuesday, December 16, 2014

Wampler Plexi-Drive

Here's Wampler's Plexi-Drive, another Marshall-in-a-box pedal. The original unit uses a 470µ capacitor for power filtering, which seems like overkill to me. I've replaced that with a 100µ cap that should do the job just fine.

Some build reports on FSB say that the 15k resistors from 9V to the drains of the J201s might need to be tweaked to bias the JFETs correctly (4.5v), so either socket those positions or use trimpots. Also, if the tone control is too dark sounding for your taste, replace that A25k pot with an A500k to brighten things up.




18 comments:

  1. i fitted mine with trimpots for the drains of those j201's, i had breadboarded something like it just before and figured it was very sensitive to bias in order to get good tone out of it, but when you come around the good numbers its awesome. ill try the tone pot swap and might thinker with the bass switch...we can never have enough options can we ? :-p

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  2. Hi, I have a 3 pin on/off switch. Is it possible to use it instead of the spst by connecting the middle as SW2 and an outer leg as SW1? Thanks for the great posts. Having fun with some of your layouts.

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  3. Hi :)

    First, thanks for your blog, it's amazing !!! :D

    The stock tone control is very useless, i recommend to put a 47nf for the tonality condensator (10nf). It works very very well ;)

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  4. I make a tweak i remove the bass switch, and I put 1M Log potentiometer to control the amount of bass, like the original two channels from Plexi, Normal and Bright.

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  5. hello, I just finished but it has very low volume. Any suggestions?

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    Replies
    1. You might need to adjust the resistors that are feeding voltage to the drains of the JFETs.

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    2. Ready, thank you very much!!!! This pedal is great !!!!

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  6. My two years old plexidrive stop saturate,now pedal sounds like a crunch box,the original distortion disappeared ,bias at 4,5 but no distortion,help!

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  7. hello ,
    What is the size of the printed plate?

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  8. What is j201's replacement? In our country i can't get it because it was discontinued.

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  9. work for me: https://www.youtube.com/watch?v=0y6JulnZQM8

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  10. This comment has been removed by the author.

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  11. Built it, love it, better than my clone TS808.

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