Electronic – Need help with an IR demodulation circuit

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!

Check that the virtual ground is stable, then double check all the capacitor and resistor values (and presence) in the affected filter.

I suspect that one or more is off by 10:1 or something like that. If the 680 ohm resistors have 3-digit markings, they should be 681 not 680.