It seems like a simple question, but I've gotten drastically different responses from different people. How do you calculate the differential input impedance for an amplifier like this:
What if you keep your source between the two inputs, but ground one? Does the impedance now change?
If you connected two separate sources from ground to each input (or a single common-mode source?), what input impedances do they see?
And so on. I have been very confused with people telling me I'm not taking "negative impedance" into account and such.
Is it possible to measure the input impedance with a standard ohmmeter or RCL meter? (As long as the amp doesn't clip, of course.)