I'm trying to build an amplifier with Op amp (TL072). I built a simple circuit like this
But I don't get anything on output. Weird thing is, I get huge amplification if I don't connect R_f and R_2. As soon as I put any resistor there, my output drops to 0.
I've also simulated a random 2 op amps in LTSpice and this exact circuit doesn't work there either.
I want only positive half of the signal to be amplified. Do I still need to do N.I.bias?
Also, I'm starting to doubt if my opamps are good. I've also made voltage follower (wire from output to - input) and my opamps are still getting a huge amplification on the output.
They are very useful devices, but certainly not magical.
Both inputs need a path for their input bias current no matter how small it is.
Also if you want to operate them from a single-supply they need to be single-supply or rail-rail types, or the inputs need to be biased at 1/2 the supply voltage (virtual ground).