Can someone recommend a good mic preamp circuit?

[audioguru]

I am sorry I connected the new 100uf capacitor to your synthesized ground when it was supposed to filter the battery voltage.
I have made many opamp circuits with a single-polarity supply but none used your synthesized ground.
They simply had the input of the opamp biased with a filtered half-the-supply-voltage then the circuit ground, input ground, output ground and all filter capcitors are connected to the negative terminal of the battery.

A little 9v battery has a fairly high internal resistance that increases as it is used so its voltage jumps up and down with the signal if it is not filtered. Also ALL opamps need a power supply filter capacitor to prevent oscillation.

 

[alec_t]

A little 9v battery has a fairly high internal resistance that increases as it is used so its voltage jumps up and down with the signal if it is not filtered. Also ALL opamps need a power supply filter capacitor to prevent oscillation.

In the second circuit I proposed, C3 and C4 are intended to 'AC-short' V+ and V- to ground and to each other at audio frequencies. So the internal resistance of the battery is shunted by a low impedance. Won't that provide adequate filtering and oscillation suppression? In simulation, I see only ~380uV of 'jumping up and down' of V+ and V- even when the battery internal resistance is as high as 500 ohm; and no sign of oscillation.

 

[audioguru]

Your C3 should be across the battery so it doesn't couple half the supply fluctuations into the synthesized ground.

 

[alec_t]

I would agree with post #23 if the '0V' reference were the negative terminal of the battery, as in the circuit arrangement described in post #21; but in my circuit things are symmetrical about, and all voltages are referenced to, the battery mid-point. So I would expect whatever V+ fluctuation gets passed to ground via C3 to be cancelled out by an equal and opposite V- fluctuation passed via C4 (since C3 = C4). Isn't that the case?

 

[audioguru]

You don't need a synthetic "virtual ground" because the input bias current of an opamp is extremely small.
Simply bias the input of the opamp at filtered half the supply voltage and capacitive-couple the input, feedback and output to the ground that is 0V.

 

[alec_t]

That will certainly do it (assuming your 0V/ground is the battery negative terminal), and is the more conventional approach. But I like to try the unconventional approach .