Build an op amp with three discrete transistors
by Lyle Russell Williams: You can use three discrete transistors to build an operational amplifier with an open-loop gain greater than 1 million (Figure 1). You bias the output at approximately one-half the supply voltage using the combined voltage drops across zener diode D1, the emitter-base voltage of input transistor Q1, and the 1V drop across 1-MΩ feedback resistor R2.
by Lyle Russell Williams:
You can use three discrete transistors to build an operational amplifier with an open-loop gain greater than 1 million (Figure 1). You bias the output at approximately one-half the supply voltage using the combined voltage drops across zener diode D1, the emitter-base voltage of input transistor Q1, and the 1V drop across 1-MΩ feedback resistor R2.
Build an op amp with three discrete transistors – [Link]
It is an inverting amplifier, not an opamp.
An opamp has a differential input, a very high input impedance and a very low output impedance. This amplifier does not have these qualities.