A classic circuit of regulation of tone of three way, with which we can regulate low, mid and high frequencies, of acoustic signal. The boost/cut can be regulated in the range of ± 18 dB/oct. In the circuit the supply is ± 15V, but can be also supplied with alone supply + 9 until + 30V, it is enough it is connected pin the 4 IC1, in the 0V and is connected the circuit with as it appears in fig. 2, giving half the supply in the not inverting entry of IC1, in the 5 and 3 equivalents, which are henceforth not connected in the ground.
circuit from http://users.otenet.gr/~athsam/3_band_eq.htm