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Unknown Pedal, Bias Problem

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  • Unknown Pedal, Bias Problem

    Hi All, Long story short I was given the task of resurrecting this custom built pedal. It was built about the mid 70's. Its 2 circuits in one box, a germanium fuzz and...... im not really sure to be honest. I think its silicon fuzz but Im new to the pedal scene (69' spec SuperBass clone straight in). The first thing i did was replace all the electrolytics. The germanium circuit works great. The other side sounds low signal until you wail on the strings which from the help of GEOFX's debugging page I figured out thats a biasing problem. My voltages on the transistors are definitely a problem. So following the example I replaced what i thought to be bad components until I replaced all the components. So i believe its a connection issue. My question is with the vast knowledge of circuits everyone on the forums has, would you be able to help me find where the connection problem might be, as i don't have a schematic?

    My voltages are
    Q1(closest to input)E-1.34 B-0.59 C-0.00
    Q2 E-0.68 B-1.34 C-0.67


    Thanks,
    Frankie

  • #2
    Originally posted by UnluckyFett View Post
    My voltages are
    Q1(closest to input)E-1.34 B-0.59 C-0.00
    Q2 E-0.68 B-1.34 C-0.67
    Perhaps you could assist us in helping by at least tell us what transistors these are. NPN? PNP? Maybe a photo of the unit and board.

    Comment


    • #3
      Ooops sorry my bad. They are GE-17 NPN transistors. I will post some pics when I get home. I started tracing the circuit with a meter in a sense, that might help. Sorry for the lack of info. I was in a rush.
      Thanks,
      Frankie

      Comment


      • #4
        I apologize for my sloppy attempt at following the circuit. I figured knowing what has continuity where was better than nothing. Ive replaced every component except the diodes and thats because i dont know what to replace them with. Will a standard silicon diode work?

        Click image for larger version

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        ^^^^^^Above 3 from same perspective, jacks on left pots/switch on right
        Click image for larger version

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        The 2 pots on the left are for the germanium side.

        Thanks,
        Frankie

        Comment


        • #5
          I checked the diodes and the forward voltage drop is correct for all of them. I re-flowed all the solder in the circuit and no changes. Voltages are still the same. according to GEOFX "the collector must be more positive than the base; the base must be more positive than the emitter by about 0.4 to 0.7V for silicon, and 0.0 to 0.3 for germanium; the emitter should be the most negative pin" the collector on Q1 is 0.00V which is connected to the diodes and electrolytics but one of the diodes goes back to a resistor then to 9v. Is it possible that resistor is the wrong value? Therefore the "power section" isn't getting voltage? Because there is continuity between all mentioned points it leads me to believe its maybe a value issue?

          Comment

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