The main component of this 3 band graphic equalizer is LM833 produced by National Semiconductor. LM833 has a very low noise, and a band / amplifier of 15MHz and a rise speed of 7V/s. The cut points for low frequencies are 200 Hz and 2 Khz for high frequencies. Maximum attenuation is 16 dB. The total gain of this sound equalizer is 0 dB but can be changed by changing R2.
You may want to add one capacitor at A2 output because of the continous voltage variations once we trim the potentiometers.