Ul, an FET op amp needs a bipolar voltage atpins 4 and 7 with a common ground for optimum gain. You can calculate the gain by dividing R2 by Rl. Zero-set balance can be had through pins i and 5 through R3. Put a voltmeter between pin 6 and ground and adjust R3 for zero voltage. Once you`ve established that, you can measure the ohmic resistance at each side of R3`s center tap and replace the potentiometer with fixed resistors.
R6, R7, RS,and C3 forrn a tone control that will give you added bass boost, if needed;