Audio Equalizer

5 bands active filter equalizer

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5 bands audio equalizer based in active filter of 5th order in Sallen-Key configuration.
The system has an input of audio frequencies by an aux cord, this signal es processed by an structure of lowpass, highpass and bandpass filters which allows the equalization of the input.


To understand the electrical schematic and actual working system of this project we resort to the previous knowledge about filters, and made a summary of these so that our calculations and design are understood:

Electronic Filter: is an element that discriminates a certain frequency or range of frequencies of an electrical signal that passes through it, being able to modify both its amplitude and its phase. In our project we use them to "alter" certain frequencies.

The topology of our equalizer includes a Low Pass filter of 62 HZ, 3 filters Pass band of 500 Hz, 1K Hz and 4K Hz and a high Pass filter of 8K Hz. These filters were chosen to create a device that modifies the amplitude of our signal, which translates into different amplitudes for each frequency band, that is, an equalizer.

In summary, each filter performs a different filtering action:

Low Pass Filter: A low pass filter corresponds to an electronic filter characterized by allowing the passage of lower frequencies and attenuate the higher frequencies.

High Pass Filter: A high pass filter is a type of electronic filter whose frequency response attenuates the low frequency components but not the high frequency ones, these can even be amplified in the active filters. It should be noted that the high or low frequency is a relative term that will depend on the design and the application.

Band Pass Filter: A band pass filter is a type of electronic filter that lets a certain frequency range of a signal pass and attenuates the passage of the rest.



High Pass Filter, fc = 8kHz

Band Pass Filter fo = 1kHz, BW = 200Hz

Band Pass Filter fo = 500Hz, BW = 100Hz

Band Pass Filter fo = 4kHz, BW = 800Hz

Low Pass Filter  fc = 62Hz


Filter Pro Tool

fpd - 10.25 kB - 10/14/2018 at 23:57



Filter Pro Tool

fpd - 9.42 kB - 10/14/2018 at 23:57



Filter Pro Tool

fpd - 10.25 kB - 10/14/2018 at 23:57



Filter Pro Tool

fpd - 10.25 kB - 10/14/2018 at 23:57



Filter Pro Tool

fpd - 10.25 kB - 10/14/2018 at 23:57


View all 8 files

  • 1 × Resistors Various Values, 1/4 W (Number will depend on the values sold)
  • 1 × Ceramic Capacitor Various Values (Number will depend on the values sold)
  • 4 × tl084 Amplifier and Linear ICs / Operational Amplifiers
  • 1 × Electrolytic Capacitor Various Values (Number will depend on the values sold)

  • 1
    Filter Generator

    The filters were generated using the Filter Pro tool; from which, we were able to obtain the appropriate topologies, as well as the value of the necessary components.

    Low Pass Filter, 62 Hz:

    Pass Band Filter, 500 Hz:

    Pass Band Filter, 1K Hz:

    Pass Band Filter, 4K Hz:

    High Pass Filter, 8K Hz:

View all instructions

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Spencer Williams wrote 12/06/2018 at 18:15 point

Could you please elaborate on your usage for this circuit? The widths of the bandpass filters are quite narrow and it appears that most all of the audio spectrum will be filtered out. What is the reasoning for the frequency bands chosen?

  Are you sure? yes | no

Lilia Lobato wrote 12/08/2018 at 17:33 point

Hi! This circuit was my final project for an university class (circuit analysis in the frequency domain) so its usage was to demonstrate how its possible to filter any frequency and mimic an equalizer... In the spot I think that in order to have a real world usage we would need to modify some widths and choose specifics frequencies to make a useful equalizer or to filter noise. 

But short answer, it doesn't have a real world application it's pedagogic. 

  Are you sure? yes | no

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