![]() Thus, the output signal will be phase shifted 180 degrees and be amplified by the ratio of R4*Rpot/( R3*(R4 + Rpot) ). The gain of a common emitter amplifier will be approximately -(R4||Rpot)/R3, where Rpot is the resistance of the potentiometer, and the symbol || is to denote R4 and Rpot being in parallel: R4||Rpot = (R4*Rpot)/(R4 + Rpot). To reiterate, only R1, R2, and the voltage supply is setting the bias voltage for the transistor. From a small signal perspective, R3 and R4 are isolated from the base of the transistor. I would not say R4 and R3 are not bias resistors, that terminology is a bit misleading. The bias voltage comes from the voltage divider formed with R1 and R2, here the bias voltage is simply VccR2/(R1+R2). The transistor here is laid out in common emitter topology. Here is a global schematic for what does what: (click to enlarge) If you look carefuly, you can see that the last stage of the Big Muff circuit is exactly the same! A LPB1 circuit is used to increase the final volume. Wired as a variable resistor defines the final volume. ![]() If you increase R4, there will be lessĪ second 0.1uF coupling capacitor that prevents DC currentįrom the battery to go out of the circuit. If you increase R4,Īmplification will be larger. R4 and R3 will define the amount of amplification. The silicon transistor is a 2n5088 (originally a 2n5133 - same transistors that were used in the Big Muff later), wired as a common emitter. (R2 and R1), to provide a certain voltage to the base of the Then, there are two resistors forming a voltage divider If you increase C1 value, more bass will go : by changing its value, you can modulate the amount of bass going With the R2 resistance, it forms a high pass filter First, there is a 0.1uF coupling capacitor that prevents parasitic DC current from the guitar to go in the circuit.
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