The present invention discloses a circuit used to couple an input signal to an amplifier circuit. The circuit may contain a diode bridge coupled to an adjustable bias circuit. The current through the bias circuit can be adjusted such that the resistance of the diode bridge can be dynamically configured to change the sensitivity of the diode bridge. The bias circuit may be configured to produce a variable amount of current based on a voltage signal. In another aspect of the present invention, the output from the diode bridge is coupled to an amplifier via a clamp circuit designed to prevent the amplifier from overloading.