you really do not need a choke for a mic pre,
the more power the amp handles, the more you need a choke, to regulate the pwr supply mostly,
so if you have a big stereo amp, you do not want the pwr supply to sag with a heavy bass note,
so a choke smooths out the current feeding the amp.
with a mic pre, you really do not have these large surges of current needed to run the thing,
so a simple resistor is ok, you might need larger value caps with the resistor pi filter, no biggy
i have A/B ed a choke vs a resistor in a mic pre and heard no difference in hum reduction or sound.
the trouble you have with a cheap pwr supply in a power amp is all the current goes thru
a pwr resistor, so this creates a voltage drop across the resistor, which gets heard in the music,
the choke has a little dcr from the copper winding, but nothing compared to a dropping resistor.