Overall, with the mods discussed for stability, I think this is a fine circuit. You need an op-amp with rail-to-rail output (or close) but everything else is pretty non-critical.
I approve of the use of a 180W-capable MOSFET in this (linear) application. You could certainly use a BJT or a Darlington (or a Sziklai pair) but there's not a lot of reason to at that power level.
Similarly the op-amp may be slightly overkill- you could probably use a cheaper one, or an even more expensive precision one, but that one should be fine. There's more compromise in using op-amps with R-R input than output, and it's unnecessary in this case, so I suppose that's a point that could be improved.
I think it's a great first shot though, and don't forget power supply bypass capacitors when you build the real circuit. Good work!
I am afraid, changing the opamp type will not help. The observed effect (less damping for rising frequencies) is the typical disadvantage of the lowpass Sallen-Key topology.
The reason is as follows: For rising frequencies the "classical" output signal from the opamp decreases (as desired) - however, at the same time there is a signal arriving at the output via the feedback capacitor (the signal bypasses the opamp). This signal produces an output voltage across the finite output impedance of the opamp (the output impedance even increases for rising frequencies). Hence, this unwanted signal dominates for high frequencies and limits the damping at a fixed value.
If you need more damping for very large frequencies the only solution is to use another filter topology (Sallen-Key/negative, multi-feedback MFB, GIC,..).
The same effect can be observed for the classical inverting Miller integrator (capacitor in the feedback path).
EDIT/COMMENT: Of course, this unwanted effect can be suppressed using another buffer amplifier within the positive feedback path (driving the feedback capacitor). However, this method requires another opamp.
EDIT2: Depending on your damping requirements - it could be sufficient to use another filter topology (MFB) for the last of the three filter stages only. As another alternative, you could add a passive RC lowpass and and a buffer stage after the third filter stage.
EDIT3: Here is a simple "trick" for improving the attenuation of the existing filter circuit in the stop band: Modify the impedance level of the parts used. For example: Increase all resistors by a factor k (for example: k=10) and reduce all capacitors by the same factor. Thus, all time constants and the whole filter respose remains unchanged, but the direct way to the opamp output now contains a larger resistors (R2, R4, R6) and a smaller capacitor. This should decrease the remaining voltages at the output for very large frequencies to a value of app. **r,out/(r,out+RX)**with RX=R2, R4, R6, respectively.
Best Answer
It's an ideal op amp to learn the basics on due to its non-ideal nature. The first thing we learn is infinite input impedance, infinite gain, as well as a few other silly things. The 741 obeys none of these idealities, forcing students to learn the hard way how to cope. They see bandwidth limitations without using expensive oscillators or function generators; they see early saturation, nowhere near the rails, allowing the use of cheap multimeters. Many textbooks use the 741 as an example due to its ubiquitous availability and simple verification of non-idealities.
Today, we can buy op-amps with mV offset and noise, 100s MHz bandwidth, nA leakage, etc.. One of the most time consuming part of a design is looking for parts, especially for the inexperienced. Academics aren't experienced design engineers, and will use the parts they know, as they have better things to do than look for parts (like write that grant application, right? :). This outdated part therefor gets introduced into new designs from copying legacy modular designs, and familiarity from instruction.