MC33079 is a very good audio op-amp, but it’s bipolar, not FET. I always preferred the LF351 to the TL071 (though I‘m not sure that they aren’t the same thing these days). There’s a lot of decent JFET op amps out there these days. For your Project I’d always preferred JFET over MOSFET because of the better 1/f noise corner.

For the dual JFET circuit, JFET #2 has its gate connected to ground and a resistor between source and ground to set the current. Source of the input FET connects to its drain, and that’s your output terminal (but you’d probably already worked that out)

Because the 3 quad op amps (TL074/MC33079) used for EQ/gain sit between a bi polar (NE5532) buffer with the JFET 2sk3557 as the input connected to the guitar pickup, EQ/gain quads don't need to be high impedance FET - and their lower noise is the advantage. IMO.

Currently the topology I'm using:
input from passive pieze guitar pickup
Front end: 2sk3557 + pair BC847c
unity buffer: ne5532.a
EQ/gain: mc33079 (qty 3, or 12 op amp stages)
unity buffer: ne5532.b
out

 

Because the 3 quad op amps (TL074/MC33079) used for EQ/gain sit between a bi polar (NE5532) buffer with the JFET 2sk3557 as the input connected to the guitar pickup, EQ/gain quads don't need to be high impedance FET - and their lower noise is the advantage. IMO.

Currently the topology I'm using:
input from passive pieze guitar pickup
Front end: 2sk3557 + pair BC847c
unity buffer: ne5532.a
EQ/gain: mc33079 (qty 3, or 12 op amp stages)
unity buffer: ne5532.b
out

Agreed. The 33078/9 is a very capable op-amp, almost as good as the 5532 but only needs a fifth of the supply current, and just as capable of driving a 600Ω line (as if anyone still uses 600Ω lines)

 

I would suggest doing away with the whole discrete JFET input and simply using an OPA205 - my go-to part for interfacing with all sorts of guitar pickups, piezos included. You can easily get the equivalent noise of a single 5k resistor and a THD < 0.0005% in a practical front end design using this part. Measured, not theoretical. I've built a buffer/booster based on this, and I've used my Audio Precision to confirm the actual performance.

 

I would suggest doing away with the whole discrete JFET input and simply using an OPA205 - my go-to part for interfacing with all sorts of guitar pickups, piezos included. You can easily get the equivalent noise of a single 5k resistor and a THD < 0.0005% in a practical front end design using this part. Measured, not theoretical. I've built a buffer/booster based on this, and I've used my Audio Precision to confirm the actual performance.

Agreed. You’ll never beat an op-amp for THD. Maybe you could improve on the noise, but it won’t be easy. A 6kΩ guitar pickup would be 10nV/√Hz at room temperature, so not much point in aiming for much below 5nV/√Hz.

 

simply using an OPA205

I can't find it now but TI.COM has a paper on "audio" op-amps. They talk about low noise, high volts/uS slew rate, and different kinds of distortion.
https://www.ti.com/product-category...Match=audio op-amps&tisearch=universal_search
op-amp audio noise