"Immunising" the following design

[ampetrosillo]

I'm designing a combination HPF + boost/soft clipper for use with bass and electric guitar.

This is the general schematic:

Since I'll build straight to SMD, I want to minimise the chances of having issues with noise and/or oscillation.
U1/U2 will be an OPA1678, while U6/U8 (don't pay attention to the references) would be an NJM5532. They will both feature 0.1u MLCC caps to ground at the V+ pin, of course.
Power supply will be 9->24V.

The main points of contention are:

• would it make sense to add in a resistor (like, 1kohm) in the feedback path of the buffers (U1/U8)? I've read that sometimes this makes the design more resilient.
• what about input resistors or input capacitance?
• I'm assuming that with the aforementioned opamps, there wouldn't be any issues with phase reversal, right? Were I to use different opamps (say, a 4580 or a 4558, or a TL072) is there a way to ensure that phase reversal would never happen? I remember reading that adding a 3.9k resistor at the positive input of a non-inverting opamp sort of cures the problem.
• are there any areas that could do with some optimisation, or things I may have overlooked?

Thanks.

 

[Mark'51]

Regarding your first question, it REALLY depends on the opamp. I recently modded a preamp design of mine because the output buffer had too much gain. I reduced its gain to +1 by removing the resistor connected between ground and the inverting input, basically doing what you have proposed: and the sucker oscillated. Simulations confirmed the problem. The issue: the feedback resistor, in combination with the input capacitance of the opamp, introduced another pole so the phase margin went from OK to very bad.

This was with an OPA1656. YMMV.