Block diagram for negative feedback amplifier using the desired output signal that is provided as a set-point value "Ô" by block "S" and the feedback provided as an attenuated output β"O" by the block "E" that monitors the state of the amplifier. The amplifier gain "A" is changed by the disturbance "D" to a new value "A′", and provided the gain is large the output is "Ô"/β regardless of any alteration in gain caused by "D".