Circuit problem, help please!

Discussion in 'General Electronics Chat' started by true bypass, May 17, 2008.

  1. true bypass

    Thread Starter New Member

    May 17, 2008
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    I'm trying to build a circuit, and I've run into quite a problem. The circuit calls for two PNP transistors, but I accidentally bought NPN transistors of the same value. Is there any way I can make this circuit work with NPN transistors instead of PNP transistors?
    Here is the circuit:
    [​IMG]
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    I knew it.
    It is a guitar distortion-maker circuit from 1967.

    To use NPN transistors, swap the polarities of the battery and polarized capacitors. If the gain of the new NPN transistors are the same as the old PNP transistors then it will sound just as distorted as the original PNP circuit.

    Distortion= FUZZ. Horrible sound. Deaf people don't mind how it sounds.
    FUZZ makes people deaf. Deaf people make FUZZ sounds.
     
  3. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    That 2M2 is way too high to drive a guitar amp.
    So is the 500K.

    Look up soft limiter if you want a valve overdrive sound.
     
  4. true bypass

    Thread Starter New Member

    May 17, 2008
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    hey, thank you everyone for the help. does anyone know how i can determine which pinout of my transistors are "e" "b" and "c" with a multimeter? thanks!
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The 2M2 and 500k pot at the output are an attenuator to reduce the output level down to an ordinary guitar pickup level.

    Then this circuit can clip its head off giving severe distortion but the output level will be normal. If the output level is turned up then feedback can create sustain.
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Take a look here in the AAC E-book for the BJT check with a meter.

    hgmjr
     
  7. mrmeval

    Distinguished Member

    Jun 30, 2006
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  8. true bypass

    Thread Starter New Member

    May 17, 2008
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    hey, thank you everyone for all their help, i finally got it to work. ... now does anyone know how to add a bias control?
    :D
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    The 680k resistor is the bias resistor. It turns on the first transistor (too much because it is nearly saturated).
    Then the first transistor biases the second transistor (which is nearly cutoff).
    With one transistor nearly saturated and the other transistor nearly cutoff then the distortion is really bad. That is what a fuzz circuit is supposed to do.
     
  10. true bypass

    Thread Starter New Member

    May 17, 2008
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    Audioguru ... THANK YOU. I cannot tell you how appreciative I am for the help you have given me! However ... I have yet another question to ask. When I have my "gain" or "fuzz" potentiometer to full, it gets incredibly "staticy" and "noisy", do you have any ideas on how I could reduce that? The entire range of the potentiometer is perfect except for when it is completely maxed, and when it's maxed, it gets a little "too noisy" for a fuzz pedal.
     
  11. true bypass

    Thread Starter New Member

    May 17, 2008
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    Also, is there any way I can increase the output/volume of my pedal?
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    Now the circuit has too much output when the gain is turned to max. It depends on the input impedance of the amplifier and yours must be high so it doesn't load down the output of this circuit enough.

    Try adding a 470 ohm resistor between the emitter of the second transistor and the 5k pot. Then its max gain is reduced to 1/10th (-20dB).
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    Increase the output level by reducing the value of the 2.2M resistor. When the 2.2M resistor is shorted and the output volume control is max then the output is at a high level.
     
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