Low-Pass Filter for Audio Circuits Experiment

Objective

The objective of this experiment is to design and implement a low-pass filter (LPF) that allows audio frequencies below a certain cutoff frequency to pass while attenuating higher frequencies. This experiment will illustrate the practical applications of low-pass filters in audio processing.

Components Required

• 1 x Resistor (R)
• 1 x Capacitor (C)
• 1 x Operational Amplifier (e.g., LM358)
• 1 x Audio Signal Source (e.g., function generator or audio player)
• 1 x Oscilloscope
• Connecting Wires
• Breadboard (optional)

Theory

A low-pass filter is designed to pass signals with a frequency lower than a certain cutoff frequency while attenuating signals with frequencies higher than the cutoff frequency. The cutoff frequency \( f_c \) can be calculated using the formula:

• Cutoff Frequency: \( f_c = \frac{1}{2 \pi R C} \)

This relationship shows that the cutoff frequency depends on the values of the resistor and capacitor used in the circuit.

Circuit Diagram

Experimental Setup

1. Connect the components according to the circuit diagram, ensuring all connections are secure.

2. Connect the audio signal source to the input of the low-pass filter.

3. Connect the output of the low-pass filter to the input of the oscilloscope.

Procedure

1. Set up the circuit according to the circuit diagram.
2. Configure the audio signal source to produce a sine wave or audio signal.
3. Observe the output signal on the oscilloscope and record its amplitude and waveform.
4. Vary the frequency of the input signal and note how the output signal changes as it approaches the cutoff frequency.
5. Record the output amplitude at various input frequencies, particularly around the cutoff frequency.
6. Determine the cutoff frequency based on your observations and calculations.

Results and Observations

Document the output signal amplitude and characteristics for different input frequencies. Note the frequency at which the output signal starts to attenuate significantly.

Conclusion

This experiment demonstrates the operation of a low-pass filter in audio circuits, showing its ability to allow low-frequency audio signals to pass while attenuating higher frequencies. Low-pass filters are widely used in audio processing to eliminate unwanted high-frequency noise.