Circuit DIY Op Amp
While this op
amp may actually have some utility, it is intended mainly as an educational exercise. I guarantee that if you build and experiment with this circuit, you will learn and appreciate what is inside monolithic versions of the same.
There is so much to learn and know about op amps that one hardly knows where to start – I suggest that this is a good place to start. Applications include inverting amplifier, non-inverting amplifier, integrator and voltage comparator. One practical application may be a headphone amplifier. This is intended to be basic rather than exhaustive.
The recommended power source is a split power
supply (±6 to ±15V). Dispelling one common misconception, note that the ± power supplies need not be equal in voltage. If unequal, the maximum output voltage swings cannot be equal in both polarities.
Q1 & Q2 make up a differential amplifier – the differential amplifier is the foundation of the op amp, offering both inverting and non-inverting inputs so it may be used in a myriad of applications. Using matched transistors, the input voltages are closely matched – this is called the input offset voltage.
For reference, recall that a single transistor
amplifier has an input voltage of about 650mV. However, in a differential amplifier, the 650mV offsets balance each other so that the difference is generally below 10mV.