Troubleshooting TL071 to TA8207 100 Hertz hum
Your 220VAC is at 50Hz, not 100Hz. Did you measure the hum frequency?
The 100Hz might be the 12VDC with rectified hum on it that passes into the preamp input bias voltage divider. The voltage divider should be fed from an RC filter with 1k in series and 100uF to ground.
Of course the input cable from the signal source and the cable from the output of the preamp to the amplifier input must be shielded audio cables to reduce 50Hz pickup.
What is the signal source that needs such a high input impedance? This very high input impedance might pickup rectified power supply hum from nearby wiring or transformer.