This 3 band equalizer circuit is an active filter network for bass, mid and high audio ranges. It is designed around the LM833 opamp from National Semiconductors.
This opamp IC has the following charactersistics: very low noise figure, wide bandwidth and a relatively high slew rate.
How does the three band audio equalizer works
The output of this 3 way graphic equalizer is designed to be DC coupled, however due to slight DC variations through the 100K potentiometers at the feedback lines of the opamp A2, a coupling capacitor might be needed.
Technical specifications for the 3 band equalizer
The cutoff frequencies:
The midrange is a bandpass network with a center frequency of 1 kHz.
The maximum equalizer range is about 15 dB. In the middle position of potentiometer, the noise attenuation is about 90 dB with a bandwidth of 1 MHz and a gain of 0 dB. The gain can be changed through R2 using the following formula: Vu = R2/R1.