66% or better

Crank out the jams with [Dino]‘s Fuzz Face

Weekly Hack a Day feature [Dino] is back again, this time with his very own guitar pedal. It’s modeled on a three-transistor Fuzz Face clone and sounds very good in our humble opinion.

Fuzz pedals were some of the first guitar pedals on the market, and for good reason. Their easy construction and simple theory of operation (just amplify sound until the transistor saturates) made them an economical and available pedal for the legends of rock in the 60s. [Dino]‘s build follows this tradition of simplicity with a common 2N3904 transistor and a pair of BC547 Silicon transistors. We’re guessing [Dino] couldn’t find any cred-worthy and mojo-giving Germanium transistors, but the result sounds just as good as we could imagine.

To test out his pedal, [Dino] hooked up a [Jack White] style single string lap steel and turned everything up to 12*. The result is rock. Check out the build vid after the break.

Comments

  1. Balbor says:

    Nice sound!

    I’ve noticed that he’s using just one 9V battery, but in the schematics two are used.
    What would be the diference? Is it losing the negative part of the waveform coming from the guitar coil?

    • tony says:

      You can use single ended power source as long as you split the 9 volts. A common way to do this is using a resistor based voltage divider, or with a chip like TIs TLE2426. Using the split voltage as the “virtual” ground, you have +/- 4.5 volts of potential to work with. Just tie the one side of the pick up to this ground and the other end will produce an AC voltage relative to the virtual ground.

    • Dino says:

      OOPS! Yeah I drew it wrong… hafta fix that. :)

  2. BoxOfSnoo says:

    The clipping diodes at the end of the circuit shouldn’t normally be necessary for a fuzz, if he had a higher output pickup it might fuzz without it. It’s a cool addition though. Rock, and all that.

    And silicon transistors can have loads of mojo, as long as you use a rubber band to keep the enclosure closed, and not screws.

  3. Alex Rossie says:

    Looks like his o-scope has had a heart attack ;p or LBBB at least :D

  4. Chadwick Roberts says:

    Technically a transistor has to be saturated to act as an amplifier (It is a voltage controlled resistor if it is not saturated.) To get distortion, the transistor has to be configured to run up against the plus and minus rail voltages.

    • Aussietech says:

      Oops, I don’t think you meant to say that.

      A transistor that is “saturated” is turned hard on; an increase in base current no longer produces a proportionate increase in collector current (Hfe) and the stage gain falls to zero.

      It is similar to the opposite case where the device is “cut off” and the base voltage is below the base cut-in voltage of Vgamma (about 0.65V for a silicon transistor and 0.1V for a germanium), no base current is flowing so no collector current is flowing, and the gain is again zero.

      @Balbor The object of the bias resistors (R1 and R3), here connected between collector and base, is to bias the device(s) at rest between these two extremes allowing (fairly) undistorted amplification of both +ve and -ve halves of the input waveform.

      @BoxOfSnoo The main reason for the back-to-back clipper diodes on the output is that without them the output into the following guitar amp could (would) be about 9V pk-pk (or whatever the supply is) which is a tad excessive, and limiting it to +/-0.7V will normally be more than sufficient level.

  5. Dino says:

    I have a couple old Sanyo 2SB405 PNP Germanium transistors stashed in a parts drawer… I originally tried building this project with them but it didn’t work… they might be toast for all I know. I should test them sometime.

  6. Mattster says:

    Dino,
    I pull germanium transistors from old equipment but I found, as did Tom Sholz of Boston did, is using two LED’s connected cathode to anode sound just as good as germanium due to the fact they have a softer distortion than a silicon transistor. I also have a back of NOS germanium transistors if you need some. email me

    Mattster

  7. zuul says:

    I built the dallas arbiter fuzz face… schematic is pretty simple and there are some nte equivlant transistors if you cant find the orig

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