Circuit diagram:

Parts:

P1,___________100K Linear Potentiometer
P2_____________10K Linear Potentiometer

R1,R2,_________15K 1/4W Resistors
R3,R4,R11,R12_100K 1/4W Resistors
R5,R6__________22K 1/4W Resistors
R7,R8_________390K 1/4W Resistors
R9,R10________560R 1/4W Resistors
R13___________220R 1/4W Resistor

C1,C2_________330nF 63V Polyester Capacitors
C3,C8_________100µF 25V Electrolytic Capacitors
C4,C5__________10pF 63V Ceramic Capacitors
C6,C7___________4µ7 63V Electrolytic Capacitors

IC1___________TL062 Low current BIFET Dual Op-Amp