[quote author="analag"]Show us a design, xvlk.[/quote]
Why I may be person to show design ???? Design
of input of the mic amp is tradeoff. Tradeoff between
noise and/or distortion.
Input stage must be concepted for low noise,
you want to have low noise for low input impedance,
you must use adequate devices at adequate bias,
there are catalogue data for determine that optimality,
you can use input transformers or paraleling components for
noise matching as you want, but remember: if you use paralel components
instead of transformers, you must adequately enlarge bias (and collector) currents.
If you use feedback, you must use that feedback network, which itself
not degrade noise figure to nonusability (like your R1/R2)
If you have 200 ohm noise resistance of mic, theese two resistors
degrade noise figure of your amp by:
10*log10(2000/200) = 10 dB. , this decreases only feedback resistors,
even though next circuits are noiseless.
My design of mic amp ?
I still think, that optimal mic amp on a silicon must have at least
current output. It must be transconductancy - amp.
No compromises, no other solvings.
Look to old Harris catalogue. If one integrated circuit
have in voltage mode 90 dB of dynamic range, in current mode
have 140 dB.
Designs based on voltage amplification belongs to the triode
era and trough invention of pentode or transistor they can not be justified.
xvlk
