I forgotten I have designed a mic preamp using my discrete op amp but it's exspensive to realize.
In Italy, very important studio recording think It's a top level preamp and they prefer it to ams neve 1073.
It's for international market and will cost 1800 euro.
Also I have designed a mic preamp using integrated op amp, it's cheap and not critic. I could give you the schematic, I haven't realized it but I have simulated it only, and it runs well.
There are not trimmers or regulations in the circuit.