Fuzz Face Mini Trim Pot

Discussion in 'The Stomp Box' started by harrisonfender, Mar 1, 2015.

  1. harrisonfender

    harrisonfender Tele-Meister

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    Just bought myself an FFM3 (Hendrix) fuzz face, and on inspecting the insides I came across a trim pot, does anyone know what it does? I just don't want to mess around with it without knowing what it does. Thanks in advance for any input!
     
  2. Iago

    Iago Friend of Leo's

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    Probably a bias control. Make a tiny mark on the trimpot so you can put it back to the stock position and have fun messing with it. Low positions will probably give your a gated, sputtery sound while crancking it up some more will give you a cleaner, louder sound that cleans up better with the volume control.
     
  3. luckett

    luckett Banned

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    If you have a multimeter, check to see that it's got 4.5V on the transistor side of the trimmer with a fresh 9V battery before marking it. That's the "standard" voltage that fuzz faces are usually set at.
     
  4. Iago

    Iago Friend of Leo's

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    If I'm not mistaken, the Hendrix fuzz is factory set to 5.5-6V. I would like to know if the OP could confirm that!
     
  5. harrisonfender

    harrisonfender Tele-Meister

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    I haven't got a multimeter, but will try to pick one up later to test this out, thanks for the info guys
     
  6. luckett

    luckett Banned

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    You're probably more right than I am. I was just going by the generic starting point for bias setting. Are all dunlop/mxr silicons set that high or is it just the Hendrix model?
     
  7. harrisonfender

    harrisonfender Tele-Meister

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    Well, I found an old multimeter and got it working, but under the hood of the fuzz face, there's nowhere around the trim pot to contact to because of the PCB!

    But after testing the pot I can confirm that it definitely sounds like it's changing the bias, counter clockwise gets spitty and more fizzy, with some sort of gateing effect. Whereas clockwise it starts to sound more like a distortion than a fuzz to my ears.

    Out of the factory the dial was set to about 3/4 of the way clockwise. I set it a bit lower around 1/3-1/2 of the way up, I liked the sound much better like this
     
  8. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    Can you reach the legs of the transistors with your probe?
    [​IMG]
     
  9. hongaku

    hongaku Tele-Afflicted

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    Where do you place the probe(s), exactly (using the pic you provided as reference, of course)?
     
  10. waparker4

    waparker4 Doctor of Teleocity Ad Free Member

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    I measure all three legs of each transistor

    If the circuit is working right, there's only one that's close to 4.5V

    and the other transistor should have 1 leg at 0 volts.

    Code:
    Component Location Voltage
    9 volt power supply 9v
    Q1 Collector 1.4v
    Base 0.6v
    Emitter 0.0v
    Q2 Collector 4.5v (if you use a trimmer,
    you can set the voltage)
    Base 1.4v
    Emitter 0.8v
     
  11. hongaku

    hongaku Tele-Afflicted

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    Cool; thanks!
     
  12. harrisonfender

    harrisonfender Tele-Meister

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    Yep, I managed to do it in the end, it measures 5.8V on the factory setting on my Hendrix, I set it to just above 2V for my own use, it seems like there's a very steep taper on the trim pot. From the top it reads 10V (when using a 9V PSU?) and goes down to 0.6V when all the way clockwise. At the half way point it 2.5V.
     
  13. harrisonfender

    harrisonfender Tele-Meister

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    Another thing I noticed with this pedal that's rather unusual is that with p90s (but no other pickup types), as you roll down your tone control the tone actually gets brighter instead of darker. What's that about? Doesn't happen with my Baja Tele or SGJ, but does with a Casino for example
     
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