Here's how I handle the mic pre cards. These are a dual opamp inverter design that causes a secondary transformer impedance shift with gain variation.
At low gains the transformer sees 120k ohms, at high gains it sees 22k ohms. This causes damping at low gains and overshoot at high gains, constantly changing with the gain setting.
To fix this, set the first stage into a non inverting configuration.
Cut the trace from IC 13 pin 3 to ground. Cut the trace from R101
(22k) that goes to the transformer yellow wire. Connect the yellow transformer wire to pin 3, connect R101
to ground. Add a 100k resistor from pin 3 of IC 13 to ground. Reverse the red and black wires on the XLR connector to retain phase. Add a 10 pf mono ceramic NPO cap into that empty feedback spot next to the second opamp, IC 12. Change C38, the 22 uf tantalum cap to a Panasonic FM 220 uf 25 v cap. Use another one for C36. Add a pair of .1 uf mono ceramic caps from pin's 4 and 7 to ground on one of the opamps for power supply decoupling.
For air, add a Wima MKP-2 .01 uf 630v caps across C36 and C38.
Now you can play with opamps. Fet opamps are the rule here as bipolar input opamps with their high bias currents will cause scratch across the gain pot when turned. I like the OP134, the OP627, OP-42, and AD825 in this location.
For even better sonics, replace the transformer with a Jensen JT-115KE and change the 100k resistor from pin 3 to ground with a 150k ohm resistor.
BTW, similar work can be done to the rest of the module, although this much re-work isn't necessary. This was done to fix the Oram/Toft mic pre "mistakes".