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In article m writes:

can i just put a 1k resistor across pins 2 and 3? to my understanding
this degrades CMRR, since the differential signal is knocked down, but
not the common mode. how much would CMRR degrade in dB with a preamp
with a ~5k input Z?

It's early in the morning so I'm not sure if you're asking the right
question, or if this is the right answer, but off the top of my head,
I wouldn't expect any degradation in common mode rejection since
you're reducing the amplitude of each leg of the signal equally. You
might have a measurable reduction in signal-to-noise ratio since
you're reducing the output level of the microphone, and will need more
gain for the same preamp output level at a given SPL going into the
mic. Purists will add the noise generated by the resistor to your hit
budget.

However, I really don't see that hanging a 1K resistor across the
output of an SM57 is going to help things all that much, if at all.
Why don't you just try it, and see:

1) if it sounds better with the resistor in place and
2) if there's a noticable increase in noise.

Then make your decision as to whether it's a worthwhile modification.

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