What to do with an extra op-amp?

[puretube]

Extra op-amp adds Baxendall tone stack. Not sure if this is correct? I think this needs a bias voltage at the + of ID1_D (pin 12)

Yes, it does some bias, but you could just remove C8 and let it pick up the bias level from the previous op-amp stage.

In general, if you do that multiple times or with high gain stages, you finish up amplifying all the offsets up to a serious level, but in this case I doubt that would be a problem and the following cap C10 blocks any offset from making it to anything downstream anyway. So just put a wire link where C8 is and you're good for that one too.

The others all look fine, btw. Nice work.

No cap between R13 and GND?

[antonis]

No cap between R13 and GND?

For a gain of 1.0045 and C10 presence on output, such design flaws should be considered negligible..

[anotherjim]

Well, lets go through it...
Typos first. We know what you meant, but 480R is probably 470R and 2m2 is 2M2 (mega not milli).
Omissions. Bias resistor to pin 12 and the value of C8. The value of both to be sized for the lowest bass, but with the tone controls there that can do that job, it can be set for 20Hz or lower. The DC blocking cap from R13 to ground.

That output stage. A basic buffer (just wire for feedback) will be fine here, no need for a complex feedback network at all. R14 will protect against instability. In fact, the tone section is quite capable of driving the output on its own. I think you may have thought that the non-inverting output amp will allow C9 to set the upper-frequency limit and keep the opamp stable, but a non-inverting amp always copies the +input signal to the output, so C9 will have a negligible effect. If you want C9 to work for you, make the output stage inverting with equal Rf/Rin. 10k's will be fine and you can add C9 feedback to set the treble cut. Incidentally, the tone block is inverting, so an inverting output stage will maintain true signal polarity through the effect.

As an aside, you may lose love for the sound of a TL074 opamp clipping which the 2nd stage can. If you fit some sockets (turned pin) across the gain pot lugs 1 & 3, you can add a back to back pair of LEDs to act as soft clippers. This will prevent the opamp clipping while still giving plenty of drive to the diode hard clippers.