DIY Guitar Pedals 7 Min Fuzz Manual - Página 14

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3.1 Input Impedance and High Pass Filter.

As covered in the Bass Control Mod section, C1 forms a first order high pass filter together with the input impedance of

Q1. The input impedance is also different for negative and positive swings because it is partially controlled by D1. For the

negative swing, the input impedance is very low and changes with the amplitude of the signal. That means only the

higher frequencies make it through. For the positive swing, the input impedance is mainly determined by the h

of the

transistor and can be quite high. That means lower frequencies come through on that half.

Because of swing differences of the signal vs the diode chosen vs the transistor chosen, values to calculate the high pass

fc = 1 / (2 ⋅ π ⋅ R ⋅ C)

filter is complicated. Typically, the formula would be

Generally though, you can assume that larger capacitance values for C1, like 10uF, will drop the frequency cut point to a

lower frequency, allowing more bass to come through. Dropping the capacitance values to 10nF will raise the frequency

cut point to a higher frequency, cutting out more bass frequencies from coming through.

3.2 Emitter Resistance and Input Impedance.

As covered in the Gain Control Mod section, disconnecting the Q1 emitter pin from the PCB and adding an inline

potentiometer by connecting the Q1 emitter pin to pins 1 and 2 of the pot and having pin 3 of the pot return to the PCB

pad for what was the Q1 emitter pin will also decrease the gain/fuzz of the pedal but increase the input impedance and

reduce tone-sucking. Typical potentiometer values are 1K and 5K linear potentiometers. Adding a 22uF or 47uF

electrolytic capacitor in parallel to the potentiometer (positive lead on pin 2 of the potentiometer and negative lead on

pin 3 of the potentiometer) will also make the fuzz less muddy as the gain is reduced.