OP amp: TL071
Knobs (left to right):
- High: 10KHz
- Mid: 1KHz
- Low: 50Hz
- Volume
You can adjust the 2.7k resistor between op amp output and the pot terminals.
This circuit uses simple power supply of 24v (24VAC transformer with full bridge rectifier and a capacitor) and has VCC/2 as ground and 0v as -12v, so don't forget the output capacitor to filter that DC offset.
If you use the components showed here and a good PCB and wires you will get a very clean sound free of noise.
Good luck!
