Discrete TL072 Op-amp!
Operational amplifiers are such important parts of any project that have analog sections. They can amplify, compare, integrate, and do all sorts of wonderful and wacky analog mathematics. For beginners, they can be a bit confusing, and understanding how they work can take a lot of reading and experience. But this fully discrete TL072 replica allows you to probe around the inner workings of an operational amplifier! We’ve seen other chips like the NE555 and the LM324 in discrete form and they can be very educational (not to mention fun!) but this one is designed to be usable both in-circuit and on a breadboard.
The TL07x series has a long history of being used in audio circuits as preamplifiers. The final digit in the model number denotes how many individual op-amps are in a package, so the TL072 has 2, the TL074 has 4, etc. The internal schematic is available from most manufacturers, including this one from ST which shows every transistor. One of the reasons the TL07x series is so widely used in audio is the FET inputs on each op-amp, which present an extremely high impedance to the circuit and therefore won’t draw current from the audio circuit. This allows it to be used in very sensitive, low-noise circuits while still providing high gain and good bandwidth.
If you’ve ever wanted to poke around inside an operating … operational amplifier, then definitely check out this project from Denjhang’s Retro Hardware.