This is an op-amp implementation of a Vox style wah, with the inductor replaced by a gyrator circuit. With the component values given the frequency response is similar to a standard wah. By replacing one of the resistors with a potentiometer the simulated inductance can be made continuously variable.
Currently this circuit has an unacceptable level of background hiss and is therefore reverted to experimental status. I will post a new version when I've got rid of the wretched noise.