# Calculating gain of an overall system. Analogue electronics

Our professor has given us a review for a upcoming exam. But he has never done anything like this question and it has stumped a quite few of us. We are hoping someone can walk us through this so we can understand, as he will not assist.

"A modular two amplifier system consists of a first stage amplifier with an open loop gain of 100, an input impedance of 25kΩ and an output impedance of 2kΩ, and a second stage with an input impedance of 2kΩ and an open loop gain of 50 and an output impedance of 500Ω.

Calculate the gain of the overall system.

Using a single op-amp, specify a third modular amplifier, using the original two in the order or otherwise, such that the input impedance of the overall system is 20kΩ, the output impedance is 2kΩ, and the magnitude of the overall voltage gain is 2000."

I thought you could just multiply the gains (gain = - Z2/Z1) of each op amp together, but some classmates disagree with me.

Should I approach it with op amps or signal circuit equivalents? Does a voltage divider have anything to do with it?

I can attach screenshots of circuit diagrams we have tried.

• It would be nice to know whether he means power gain, voltage gain or current gain. Given the rest of the question, I can make a guess, but it IS just a guess... Apr 24, 2017 at 16:16
• he means voltage gain Apr 24, 2017 at 16:18
• Like any other problem: solve it step-by-step. Figure out what the first amp does in the presence of the input and output impedances, and feed that signal to the second. BTW, if you have two simplified methods (opamp, signal equiv.), run them both and see if the answers are largely different. Apr 25, 2017 at 15:17