I used the term solid state instead of op amp since most people don’t know the difference. Obviously I was wrong and some do know the difference.
They are both, FET and op amp, solid state but they achieve results in a very different ways thus having different sounds. FET boost tend to have a warmer color to the tone, more tube-like but not quite the pleasant warmth of a tube preamp. An OpAmp in my opinion sounds sterile, very linear in response, almost too linear. On the upside, the linearity makes them very predictable when designing a boost circuit.
Building FET preamps can be difficult since they are susceptible to noise and wide or increasing Q’s. In a bass preamp the frequency range that needs to be worked with to be most effective is fairly small.
Roger has determined that adding a mid control to the FET circuit affected the current bass & treble FET in a negative way and he decided not to go that route. He opted (no pun intended) for an op amp mid circuit so the Q width and Frequency could be adjusted since an op amp’s operation is primarily a mathematical algorithm.
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... single coil traditional J pickup, but buffered by a preamp set mostly 'neutral'.... some organic grind, but a bit more deep bass and a bit more 'sparkle' up top due to the buffering, and the slight voicing built into a preamp like the Sadowky.
