Discrete OPAMP. Non-Inverting Amp

There is a solution, even if some user here think EC is just a toy, right Lenny? However, the problem is a so called offset voltage or current any bjt opamp design has. Do the following: place at + opamp input also a 1kohm in series to your AC source and add to the AC source a 9.09mV DC offset. Now it should also start in closed loop configuration. A detailed explanation might follow, sorry. Only this, your differnetial input amp need some current to work, around 1mA you have to share on two transistors to get in sum 2mA to bring it in balance. Hfe of your bjts is 100. 1mA /100 is ~10uA this cause at negative input at 1kOhm ~10mV. To balance this you need at + terminal the same "error". Hope this helps.

Thanks hurz.

You are welcome!

Hey hurz posted the MOSFET version, it somehow doesn't have the error check it out.

Yes, because the mosfets do not have DC leakage current (EC perfect model), just some AC cap current which seems to be no issue for low frequencies.