Build This Homemade Op-Amp and Learn How They Work

One of our favorite integrated circuits is the incredible operational amplifier. Using them in a certain takes a certain level of understanding. But how many people understand how they work internally? Mitsuru Yamada shares his electronics project in hopes of inspiring others. With this Homemade Operational Amplifier, the OPM_01, Yamada helps teach how these remarkable devices work.

You might recognize Yamada's name. Previously, we've featured some of his retro-inspired work. As Yamada humbly admits, the design of the circuit is not unique.

"I thought I had achieved at this circuit configuration by my own ingenuity, but when I searched the net again now, I found several similar circuits published. I guess the limitation of five transistors means that anyone can reach the same solution." — Mitsuru Yamada

However, consider that many students start their op-amp learning journey with the ua741. This relatively simple op-amp design contains almost 20 transistors. In contrast, the OPM-01's design has only 5 transistors! Using just five general-purpose NPN and PNP transistors is enough to make up the differential input, gain, and output stages of a functional op-amp. Add a couple of resistors and multi-turn potentiometers, and you have a discrete operational amplifier.

While OPM-01's design may not be unique, Yamada's simple yet straightforward explanation of the op-amp is. With the aid of his schematic, description, and a circuit, anyone can understand how operational amplifiers work (inside the package.)

A common first-circuit for op-amp learners is to build an audio amplifier. If that is the goal, the OPM-01 needs a slight modification for the output stage. That mod, also known as OPM-02, increases the transistor count to 7--depending on how you count them. Yamada's suggestion is to use Darlington transistors. They enable enough drive current for a speaker's 8-ohm load.

With such a simple bill-of-materials, anyone can build a homemade op-amp with Yamada's instructions. Check out the OPM-01 project page for a parts list, schematics, and detailed description.