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  • TooSlowTube. commented on randofo's instructable DIY Guitar Pedal1 month ago
    DIY Guitar Pedal

    I recently breadboarded a PNP silicon Fuzz Face (I'm waiting for some Germanium PNP to do it properly). It's basically the same circuit, but with opposite power rails, but I still used negative ground for the two jack sockets.You need to be able to bias it properly, to get a good sound. Replace the 10k fixed resistor from the collector of Q2 (the output transistor) to +9V, with a 470R to 1kR resistor, in series with a 5k to 22k pot (depending on the gain of your transistors).I deliberately looked through all my transistors for the lowest gain ones I had, measuring hfe (DC current gain), on a multimeter. You can make a simple test circuit to do it with any meter that can measure voltage or current. The original Fuzz Face used very low gain Germanium transistors. I found two PNP sili...see more »I recently breadboarded a PNP silicon Fuzz Face (I'm waiting for some Germanium PNP to do it properly). It's basically the same circuit, but with opposite power rails, but I still used negative ground for the two jack sockets.You need to be able to bias it properly, to get a good sound. Replace the 10k fixed resistor from the collector of Q2 (the output transistor) to +9V, with a 470R to 1kR resistor, in series with a 5k to 22k pot (depending on the gain of your transistors).I deliberately looked through all my transistors for the lowest gain ones I had, measuring hfe (DC current gain), on a multimeter. You can make a simple test circuit to do it with any meter that can measure voltage or current. The original Fuzz Face used very low gain Germanium transistors. I found two PNP silicon with a hfe of 130, which is low by modern standards.The 0.1uF input capacitor should be bigger, if you have low gain transistors - because the input impedance will be lower, which means the roll off frequency of the input decoupling will be higher. Think of the base of the transistor as a resistor to ground. For a low gain transistor, that's a small resistance. Lets call it R, and the input capacitor C. The roll off frequency is then1 / (2 x pi x R x C)below that frequency, the sound will be reduced (by 3dB per octave, I guess). So, you can see that if R is small, C needs to be big. On the original fuzz face, it was something like 2.2uF - a pretty big capacitor.Using higher gain transistors, as most of them are these days, you won't get the same sound as the original Fuzz Face, but you still will get fuzz. How much fuzz will depend on how you bias it. In my circuit, I used the normal 470R resistor in series with a 5k pot. I can adjust it from an almost clean amp sound (pot at zero Ohms), through various types of fuzz, to breaking up on everything but really loud notes, to no sound at all.Personally, I feel a bias pot that makes a useful extra control. At the very least, you should try a preset, and set it how you want it. Some people measure where they like it best then choose a fixed resistor.

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