Monday, 24 September 2012

Madbean FatPants 2012

Madbean's take on the EP Pre-amp. Info from Brian about his design:

The FatPants design began as an alternative to the “pedalized” versions of the input stage of the Echoplex that became popularized a few years ago. Over the course of the two previous versions the design has evolved, and the 2012 version is no exception. The 2012 version adds a JFET input buffer, a new Body switch for high-gain/full spectrum boost and a re-tooled output section. These changes add versatility and dimensionality to the previous design. The FatPants 2012 is capable of a wide range of boost and overdrive and will serve as a perfect compliment to push your tone into saturation while retaining note clarity and dynamics.

Fat – Sets the overall gain of the boost.
Lvl – The output volume.
Body – Selects between a mid-range and full range boost. In full range mode, it also adds additional gain.

You may encounter some scratchiness with the Fat control when the Body switch is off. This is normal. Unfortunately, this cannot be eliminated from the design without altering the overall character of the effect. The Fat control works in concert with the 22n cap to produce frequency-dependent gain. As the control is turned up, it applies increasing gain to the upward filter. This results in increased pick attack and dynamics. When the control is down, the filter is also lowered, but since the overall gain is lowered at the same time it does not “muddy up” the signal.

Setting up the FatPants:

Leave the Body switch off, set the Fat control to max. Adjust T1 until you read approximately 9v on the drain of Q2 with your multimeter. Tweak as desired for maximum gain.





16 comments:

  1. woots i love the demo! i am so gonna try to build this one as soon as my parts order arrives (by next week i hope!). mark, is the switch 2-pos spst? and what is the role of the trimmer? is it just to increase the output gain?

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    1. Yes 2 position SPST is all you need, but you'll probably find a SPDT switch cheaper so just get that and only use the middle and one of the other lugs. The trimmer biases Q2, so just rotate it until you get 9V on the drain of Q2.

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  2. Does this circuit supposed to sound like the Brain Zeltzer by Nocturno? or is it a completely different pedal?

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    1. No this is a take on the EP-Pre and EP Booster, you'll need to go one post ▼ for the Nocturne.

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  3. Ok Mark, another Verification!

    Just one small correction: Fat 3 goes to ground (not Fat 1), otherwise everything works perfect!

    Didi anyone notie I have a lot of spare time these days? lol....

    Thanks,
    Chris

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    1. Awesome thanks Chris. And yes you're on fire at the moment too! :o)

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  4. interesting.

    i have two echoplex's, never thought of using them as overdrivers. ;)

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    1. Oh Jimi, you've never lived if you haven't thought of that! :o) Jimmy Page swears by it!

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  5. This comment has been removed by the author.

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  6. A question: do you think that input buffer results absolutely crucial for the overall tone, or it can be omitted? You know, for preventing the notorious impedance problems between buffered pedals and fuzzes while in the same chain...

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  7. A question about my build. It seems the Fat control does not have much effect when the Body switch is engaged. Is that normal?

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  8. Can this run at 18v?
    I was hoping to house it with a DLS

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    1. It IS run at 18V via the ICL7660S. You can't supply it with anything greater than 9V though, the maximum input voltage of the ICL7660S is 12V.

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    2. I guess you wanna run it at 18V input just like you would for the DLS to get more headroom and beef. In that case...DON'T. You will fry the 7660S voltage doubler. I suggest you take the 7660S from the Fatpants and put the voltage doubling circuit out of the main Fatpants board and use it to double the input 9V to 18V (it's 17.5V actually). Then run the 18V in parallel to both DLS and FP boards and house them together in a single enclosure. Do you have a good schematic for a 2-in-1 configuration? Ulysses did a nice schematic back in 2007 which is great.

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  9. Thanks for the replies
    I knew the 7660 rang a bell , I Just used it on my Kingslayers
    Is there a place on this board I can tap to power the Dls

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  10. Hi Mark, Miro,

    Is there a chance of updating this great layout to include the 2013 Fatpants update?

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