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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:






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19 comments:

  1. Olav9 February 2013 at 18:38

    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. IvIark9 February 2013 at 20:30

      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. Olav11 February 2013 at 07:04

      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. mah629 February 2013 at 21:46

    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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  3. Dave13 February 2013 at 21:46

    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. rousejeremy6 March 2013 at 03:20

    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. Ross5 June 2013 at 14:54

    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. Bolshevik17 June 2013 at 04:31

    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. mirosol17 June 2013 at 05:16

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

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    2. tom k2 July 2013 at 04:52

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

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  7. okwilliam20 January 2015 at 09:55

    This comment has been removed by the author.

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  8. okwilliam21 January 2015 at 10:59

    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. Unknown20 July 2015 at 12:36

    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. Unknown16 January 2016 at 21:47

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

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  11. NHTMF12 April 2017 at 10:08

    I built this yesterday and have been playing around with it...and I don't really like it. I had initially planned to build and LFO with an LED. I have the LFO circuit on a breadboard running off its own 9v battery but I get a clicking or popping whenever the led lights up. (any ideas on how to combat this?)

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  12. Buildabox30 July 2020 at 03:17

    I'm having a strange issue with this build.
    When powered on I get no signal, just a low level hiss and then a quiet super high frequency squeal with the 50k linear pot turned fully clockwise. With no power it passes signal very quietly but I can hear the filter working when I turn the pot.

    I'm building this to go into a studio effects box so I'm skipping the footswitch and wiring straight to the in/out jacks.

    My voltages are:
    C: 8.78
    B: 8.18
    E: 0.14

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