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How to Build a 1200 to 2200 Hz Amplifier

A band-pass filter is an electronic circuit that allows a range of signals through while reducing signals outside of its frequency band. Different band-pass filter designs have response curves ranging from a sharp peak to a wide band with gently sloping sides. Using an operational amplifier, or op amp, and a handful of resistors and capacitors, you can build a band-pass filter with a wide band. The center frequency of this filter is 1,700 Hz, which is midway between 1,200 and 2,200 Hz. The filter̵7;s band is wide enough to pass these frequencies while attenuating those much higher or lower.

Things You'll Need

Solderless breadboard
LM741 operational amplifier integrated circuit
3 resistors, 10K-ohm, 1/4-watt
2 resistors, 20K-ohm,1/4-watt
2 capacitors, .01-microfarad, 50-volt
22-gauge solid wire, 7 pieces cut to 10-inch lengths
Labeling tape
Pen
Regulated 10-volt bipolar DC power supply

Instructions

- 1
  Set the LM741 op into the breadboard so that its legs straddle the slot running through the center of the board. Gently press the op into the board, making sure its pins go in straight.
- 2
  Insert one lead of one of the capacitors into the breadboard so it connects to pin 3 of the LM741. Set the remaining lead into a free column on the board ̵1; one that is not connected to any of the IC̵7;s pins. Insert one lead of the second capacitor so it connects to this column. Set its other lead into a free column. Insert one lead of a 20K-ohm resistor into this column. Connect its other lead to pin 3 of the LM741.
- 3
  Set one lead of a 10K-ohm resistor so it connects to pin 6. Connect its other lead to the breadboard column shared by the two capacitors. Insert one lead of another 10K resistor into this column. Set its other lead into an unshared column. Insert one end of a 22-gauge wire into this column. Wrap a tape label around this wire and write ̶0;Input̶1; on the label.
- 4
  Insert one end of the second 20K-ohm resistor so it connects to pin 2. Set its free lead into the column shared by the first 20K-ohm resistor and capacitor. Insert one end of the remaining 10K-ohm resistor so it connects to pin 2. Connect its free lead to the IC̵7;s pin 6. Insert one end of a wire so it also connects to pin 6. Wrap tape around this wire and label it ̶0;Output.̶1;
- 5
  Insert one end of a wire so it connects to pin 7. Connect the wire̵7;s free end to the DC power supply̵7;s positive terminal. Set one end of another wire to pin 4 and connect its free end to the power supply̵7;s negative terminal. Insert one end of three wires so they connect to the column shared by the two 20K-ohm resistors and the capacitor. Connect the end of one of these wires to the power supply̵7;s ground terminal. Twist one of the remaining two wires one turn around the wire labeled ̶0;Input.̶1; Twist the remaining wire one turn around the ̶0;Output̶1; wire.

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