I'd put the volume pot after the TL072 (why two different opamp types btw?) so that it is buffered, and the source sees a constant impedance rather than a changing one.
you can search for the Apt preamp schematic. Adding a buffer (even a simple emitter follower) as shown there will pretty much eliminate the midband interaction between bass and treble controls.
and the patent has expired ...
Hi ArnulfMind if I peg onto yout topic ? I came across some 100K potentiometers and I've got a guitar amplifier that could really use a tone stack...
i only had 2 pieces of 10k pots so i decided not to use a volume pot.
i redisgned the circuit and here is the new one. the input-buffer stage has a gain of 2.2 (6.8dB).