Saturday, 9 February 2013

Escobedo Idiot Wah

Request.

The Idiot Wah is a simple building block Bridged/Twin T filter giving a resonant low pass response. It's specifically designed for electric guitar, for simplicity and useability, making it a bit different from similar designs.  The input resistor helps the input from loading down and attenuates the input signal.  The Darlington transistor has enough gain to keep the output at about unity.  Biasing helps keep the distortion down. And most unusual, the unequal capacitors in the T network give a more useful, more musical range than the typical matched values.

VR can be a pot, an LDR, or any type of variable resistive element. Being a resistor to ground allows many different schemes to be used to control the cutoff frequency for the filter.


A quick example of the idiot wah being controlled via an LDR rather than a pot:






17 comments:

  1. Any suggestions on how to use an LDR in this? I'm trying to think of how I would vary the amount of light effecting the LDR.

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    1. The LED will need to be controlled by an LFO, with the rate being controlled by an external pot. Something like the LFO from the EA Tremolo would do the trick. If you wanted to turn it into an autowah you'd need some sort of envelope control but to be honest if you're going to do that you may as well build an autowah like the Danelectro French Fries or Doctor Q.

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    2. Aah, so another board would be required. That makes sense. I was traveling down a whole different road in my mind. Nothing but obstacles.
      For an autowah I like MadProfessor's SnowWhite very much, but the Dano FrenchFries seems a much simpler build. Might do me just fine.
      Thanks Mark.

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  2. Verified. It had my name on it so I had to build this! A very useful circuit and will probably end up doubled up with a dirt box very soon. Thanks, again.

    Mark

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    Replies
    1. Will you be doing the ROG Phoser at any point, Mark?

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  3. Built one this evening, what a fantastic little circuit. If you want my tip, get yourself an ORP12 LDR to use as a freq control, makes a great light wah.
    Thanks
    Dave

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  4. I was wondering why my video had so many hits last month. Ivlark, feel free to use any of my YouTube vids as a demo. I love your site and your dedication to providing people with the newest and oldest circuits out there. Cheers!

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  5. Hmmmm.... I wouldn't exactly call this a wah. I'm getting more of a swept filter sound, with a pretty large dead spot on the pot (50K linear.)

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  6. Is this a 50k log or linear pot? I just assumed it was 50k lin and dove right in.. This thing is pretty nifty and a great idea for a beginner project... can make things interesting before or after a really saturated fuzz pedal.

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    1. Escobedo doesn't state tapers in his schematics, but i think you'd be fine with linear.
      +m

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    2. i used a reverse log 50k and the sweep is even

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  7. This comment has been removed by the author.

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  8. hey, what kind of LDR should I use instead of the 50k pot?
    I'm getting oscillation sounds right now with the current LDR I use.

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  9. Hello!
    I would like to build this wah with some mods, but I have no idea how to do it. Could you help me, please?
    Is it possible to add a switch allowing to select a way in which FREQUENCY will be controlled? I want to achieve such effect: switch in 1st position - standard freq control with a 50k pot (as it is in the layout) and a switch in 2nd position - freq controlled by a photocell.
    And another question, how to connect a photocell and what kind of LDR should I use? You have mentioned ORP12 LDR, but I can't find it at any local store.

    I would be grateful if you could draw a layout to clarify things. I have no experience with LDR circuits.

    Thanks,
    Terry

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  10. Wanting to make this circuit soon, what exactly does the resonance switch do?
    Thanks

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