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4. Volume Control.

The output is controlled by a volume potentiometer that goes to ground, along with an output capacitor to keep any DC

current from hopping out of this pedal and into the next (or amp).

The 100nF C2 output capacitor blocks DC and provides simple high pass filtering. C2 and Volume Pot create a high pass

filter.

fc =1 / (2πRC)

⋅C

fc = 1 / (2π⋅VOL

MAX

fc = 1 / (2π⋅100K⋅100nF)

fc = 1 / (2π⋅100,000 ⋅ 0.0000001)

fc = 16Hz

With a cut of 16Hz it will block DC and any low-frequency parasitic oscillation. However, as the volume pot is turned

down, resistance to ground is decreased and the filter changes frequency position. For example, if the pot is half way:

fc = 1 / (2π⋅50K⋅100nF)

fc = 1 / (2π⋅50,000 ⋅ 0.0000001)

fc = 32Hz

So, now some of the sub bass frequencies will begin to get cut. A way to resolve this is to increase capacitance of C2 to a

1uF electrolytic or film capacitor.

4.1 Output Impedance.

The pedal output impedance also depends on the volume potentiometer position, being always less than the value of R1

(10K)

•

Volume Potentiometer at maximum volume: Zout = 10K parallel to 100K = 9K approx.

•

Volume Potentiometer at minimum volume: Zout = 10K parallel to 1K = 0.9K approx.

Ideally, a guitar pedal design aims for low output impedance, it makes the circuit to interact nicely with the rest of the

pedals on the board. 9K is not bad; most of the designs keep the output impedance below 1K but 9K is still good.

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