I just wanted to make it clear to those joining us late: LF servo resonance is not unique to an input-capacitorless design.
I'll draw the analogy that a servo is a subtractive, derived, HP filter. Any servo filter order greater than "1" is prone to peak.
Though the preamp's servo filter order may be 6 dB/octave, when combined with the capacitors that are potentially in the mic output, or the series combination of mic output's and preamp input caps, the filter order can be >6dB/octave if they're close in frequency.
Having the servo Fc known and unchanging with gain - as your servo does - makes the job easier.
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