simple opamp circuit

[shallow]

Hello;

Can you just explain what does this circuit do? Why we connect input signal to both pin2 and pin3 of the opamp?

 

[MikeMl]

R10, R11 and C3 create a "virtual ground" so the opamp can be operated on a single-supply. It is a non-inverting gain stage, with a gain of (1+39/10). Capacitively coupled, in and out. Input impedance, ~33K.

Not a very good circuit. I would do the bias circuit differently so the power supply consumption would be much lower, like this:

 

[audioguru]

Hi Mike ML,
The original circuit uses the 1uf capacitor to be a low impedance to ground for the 10k feedback resistor plus it filters any power supply ripple from the bias voltage. Your circuit does not filter the bias voltage.

I would use one capacitor to be the low impedance to ground for the 10k feedback resistor and another capacitor as the filter for the bias voltage.