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What are the relative merits of using inverting/non-inverting op-amp configurations for a microphone preamp? While searching for microphone preamp schematics based on op-amps, I have found both inverting, and non-inverting varieties.

You can have a non-inverting amplifier, which presents a massive input impedance to your microphone. The values of R1 and R2 do not alter the input impedance of the gain stage as far as I see.

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You can also use an inverting amplifier, but here you have to make sure that the value of R1 is sufficiently high so as not to load the microphone (perhaps using the rule of thumb that the input impedance should be approximately 10x the nominal impedance of the microphone).

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Aside from signal phase, are there any major differences in the outputs from these gain stages??

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    \$\begingroup\$ If you look closely you can see that they are the same circuit topology from the perspective of the op-amp. In the application the difference is just one of which input we choose as "signal" and "return". \$\endgroup\$
    – Michael Karas
    Oct 31, 2012 at 12:34
  • \$\begingroup\$ In terms of signal amplifier, they're pretty much the same, save impedance and minor other things, but if you intend to use it "live", then you may as well have a problem due to the inversion of phase which may cause oscillations. It is preferred (actually encouraged) to use non-inverting amplifier, that is, input phase = output phase, therefore you can't use "aside from phase..." as a basis of your reasoning in this. \$\endgroup\$
    – Vlad
    Oct 31, 2012 at 13:01
  • \$\begingroup\$ What kind of microphone? Electret capsule? Dynamic? Piezo? Each kind needs different circuits. \$\endgroup\$
    – endolith
    Jun 24, 2015 at 14:29

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If you just want a simple flat gain including DC around ground, then about the only meaningful difference is that the non-inverting configuration has high input impedance and the inverting a controlled input impedance referenced to ground.

The differences matter more when you want to do other things, like bring the DC gain down to 1, not load a mid-supply reference, keep turnon fast, etc.

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    \$\begingroup\$ Hi @Olin, I'm a couple years late to the party and not sure if you are even still on here. If you happen to be then it would be great if you could expand on those differences you alluded in the second part of your answer. Very interested. Thanks! \$\endgroup\$
    – Funkyeah
    Apr 1, 2015 at 21:04

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