The EM is not subtle and it would be nice to be able to dial the balance to: more uneffected + less flanged = Unity, without using an external mixer. The junction of the 13K, 10K, and 470ohm looks like a mix point. I don't understand the Color and Trim pots at all, so, I'm basically guessing that the 13K is 'feed forward,' not feedback and the mix is about 50|50.
OK, I see now.
The junction of the 13K, 10K, and 470ohm looks like a mix point. - yes, it is - first you can try to replace 13k + 10k divider by 22~25k linear pot and play with it. This way you can try full possible range, find reasonable limits and then replace it by combination of resistors and pot (e.g. 8k2 - B10k - 4k7).
There is one potential problem, 470R+47n branch - this branch forms (with "mix" resistors) passive
de-emphasis filter. Changing mix resistor values will detune this filter (bigger value will lead to less highs than on input, smaller value to more highs than on input) - you may or may not find it to be a problem during you experiments with blend pot.
Edit: There is another potential problem, overall volume may change with blend pot setting - you may or may not find it to be a problem during you experiments with blend pot as well.
One possible way around both of these problems would by adding (toggle) switch switching between two (or more) properly tuned fixed mixers with fixed ratios.
I don't understand the Color and Trim pots at all, so, I'm basically guessing that the 13K is 'feed forward,' not feedback and the mix is about 50|50. - yes.
T.
