Four Stage Jfet Guitar Preamplifier with Gain control

Discussion in 'Burnt Fingers DIY Effects' started by acranford9, Jul 15, 2013.

  1. acranford9

    acranford9 TDPRI Member

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    As a student in Electronic Engineering Technology I started designing and constructing a preamplifier that can be deliver huge amounts of gain using only x4 J201 Jfet and around a dozen resistors. By using the link listed below...



    Design equations are used to be able to design the jfet preamplifier with 4 stages instead of two.
    The files attached are the calculations, and the schematic. Note that the schematic has j201 jfet not 2N3370. It wont work properly if the 2N3370 was used. The quality of the camera might not be that good but feel free to ask any questions if you`re having any trouble understanding anything.

    Part Symbols Selected Component type
    C1 0.1 uF 100v Paper/wax Capacitor
    R3, R6, R9, R12 1 Mega ohm 1/2 Watt Resistors 10%
    R1 5.6 kili ohm 1/4 watt resistor 5%
    R2 10 kili ohm 1/4 watt resistor 5%
    R4 7.5 kili ohm 1/4 watt resistor 5%
    R5 4.3 kili ohm 1/4 watt resistor 5%
    R7 30 kili ohm 1/4 watt resistor 5%
    R8 22 kili ohm 1/4 watt resistor 5%
    R10 16 kili ohm 1/4 watt resistor 5%
    R11 12 kili ohm 1/4 watt resistor 5%
    R13 10 ohm 1/4 watt resistor 5%
    R14 10 kili ohm Audio Potentiometer
    R15, R16 1 kili ohm 1/4 watt resistor 5%
    R17 200 ohm 1/4 watt resistor 5%
    R18 1.5 kili ohm 1/4 watt resistor 5%
    C2 4.7 uF Radial Electrolytic Capacitor
    C3 10 uF Radial Electrolytic Capacitor
    C4 15 uF Radial Electrolytic Capacitor
    C5 22uF Radial Electrolytic Capacitor
    C6 100 uF Radial Electrolytic Capacitor
    Q1-Q4 Fairchild J201 JFET N-Channel
    J1 Mono 1/4 Female Jack
    J2 Stereo 1/4 Female Jack
    S1 DPDT Switch on/off
    VCC 9V Battery clip
    P1 ABS Project Box
     

    Attached Files:

  2. poiureza

    poiureza Tele-Holic

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    Well I guess the question is : "how does it sound ? "
    Looks kinda similar to a Big Muff minus the feedback paths
     
  3. R. Stratenstein

    R. Stratenstein Doctor of Teleocity Ad Free Member

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    Cool. Any chance of an audio clip?
     
  4. Relayer110

    Relayer110 TDPRI Member

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    Since you've used a label maker to indicate the various controls on your project, I might suggest you can use an excellent free program called, "Front Panel Designer" which you can find here:
    http://www.frontpanelexpress.com/.

    Its a fairly easy program to use, though its a tad limited in color range, but at least you can get your projects looking fairly professional.
    Once you've designed your panel, print it out on photographic paper, run it through a laminator, cut it out and glue it onto your project box.
    You can even print out a rough sheet to use as a template for drilling holes.
    Here are some examples of what I've done:

    [​IMG]

    [​IMG]

    [​IMG]

    I hope the above helps.
    Regards,
    Relayer :D:D:D
     
  5. poiureza

    poiureza Tele-Holic

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    Thanks for the link Relayer. Comes handy
     
  6. Relayer110

    Relayer110 TDPRI Member

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    You're welcome my friend. ;)
    Regards,
    Relayer :D:D:D
     
  7. Wampler Pedals

    Wampler Pedals Tele-Meister Vendor Member

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    good start, but I'm wondering what you are trying to accomplish sound-wise exactly. Blocking caps are huge for guitar signals, way bigger than what you really need. You also will find that adding resistance after these caps will get a better overall clipping sound and feel. It's very easy to drive a jfet into saturation so much that it compresses in an unnatural way. Also, don't forget about a tone control - you are going to want to at least put some sort of variable low pass filter at the end, but you have a great start here :)
     
  8. Wampler Pedals

    Wampler Pedals Tele-Meister Vendor Member

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    big muff is npn with diodes in a feedback channel, this is seperate jfet stages.
     
  9. cousinpaul

    cousinpaul Friend of Leo's

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    You might look at some of the RunOffGroove projects for ideas. The Umble, for example, uses four j201's.
     
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