Welcome to AAC! A thread belongs to the OP (original poster). Trying to take over someone elses thread is called hijacking, which is not allowed at All About Circuits. I have therefore given you a thread of your very own. This was split from http://forum.allaboutcircuits.com/showthread.php?t=58609 Can someone clarify to me what happens with this circuit when ,for example, a 1mV signal is brought to the input and Vcc is 5Volts so 2.5Volts at the noninverting input? If I understood the guide correctly that op amp is trying to hold both inputs at 2.5Volts so the inverting input would be at 2.5Volts and the output at gain*2.5? But how does the 1mV signal get amplified then? How does it effect the operation?