OPAMP with self adjusting gain

[casemod]

Is there a way to have a constant output when an opamp is used as an amplifier for an input signal with variable amplitude? If so, how could this be achieved?

Basically how to change the opamp gain depending on the output voltage

 

[Warpspeed]

Usual way to do this is either with a variable transconductance amplifier, or an analog multiplier.

 

[crutschow]

Look up AGC (Automatic Gain Control) circuits.

Below is the LTspice simulation of an example circuit.
As you can see, the output remains fairly constant for a varying amplitude input.

 

[Audioguru]

The AGC circuit is used on Wien Bridge oscillators and on radio stations (and for TV audio).