Basic Audio Equalizer Project

Building an audio equalizer using low-pass, band-pass and high-pass filters

Technical skills: Circuit Design, MATLAB, LTSpice

As part of the final project in ECE 20007: Electrical Engineering Fundamentals Lab, we had to build a basic audio equalizer circuit using op-amps and low-pass, band-pass and high-pass filters. The specifications were:

  • Three filters have to be used: bass with cutoff at 320Hz, mid with range of 0.32kHz to 3200kHz, and treble with cutoff at 3.2kHz
  • Amplifier output power has to be more than 400mW from 200Hz to 10khz
  • Max ripple of 15 * mV_rms from 200Hz to 10kHz
  • Volume control must be enabled

The tolerance margin of all the specifications were +/- 10%. To ensure that the combination of resistors, capacitors, and inductors fall within the tolerance margin, I coded a MATLAB program to help choose the components to build the circuit. The circuit was simulated and designed using LTSpice.

LTSpice diagrams of the three filters, Low-Pass, Band-Pass and High-Pass from left to right
Basic audio equalizer circuit

The performance of the audio equalizer and its filters were tested using frequency response analysis using oscilloscopes. The results and procedure can be found in the report below: