ELEC 101, Spring 2005
Prof. Rich Kozick

Laboratory 8
Design and Construction of a Three-Band Audio Equalizer

Pre-Lab Exercise: Analyze each circuit in Lab 7 and determine formulas for the frequency response. Include the analytical frequency response curve on your Bode plots with the experimental data, and include the plots in your lab notebook. Comment on the agreement between the theoretical and experimental frequency responses. What are the cutoff frequencies for each filter?

You do not have to include the analytical curves on your Bode plots before you come to lab. You should have the formulas for the magnitude of the frequency response before coming to lab, and then we'll do the plots during lab.

Problem: Design and construct a three-band equalizer circuit. Your circuit should include three filters: a low-pass filter that passes frequencies up to about 500 Hz, a band-pass filter that passes frequencies centered around 1073 Hz, and a high-pass filter that passes frequencies above about 2000 Hz. You should be able to adjust the gain (or amplification) of each frequency band independently. You will demonstrate the operation of your equalizer by passing music through your circuit and playing the "equalized" music through a speaker.

System Design: Use the "subsystem" circuits shown below to design your equalizer. Which circuit is the low-pass, band-pass, and high-pass filter? What is the "cutoff" frequency of each filter? How should you connect the subsystems to form your equalizer? Do you need "buffer" circuits in your design?


  1. Complete the system design, and draw the total circuit diagram in your lab notebook.
  2. Build and test the circuit. You may want to divide the work so that one lab group builds and tests the filters on one breadboard, and another lab group builds and tests the op amp portion of the circuit.
  3. Demonstrate the equalizer operation by processing music.
  4. Write a short summary of your observations in your lab notebook.