Building A 4558 opamp from scratch.

Stompboxes circuits published in magazines, books or on DIY electronics websites.

Re: Building A 4558 opamp from scratch.

Postby nr372 » 28 Apr 2016, 21:54

Discrete opamps are a fun learning tool, as you can thoroughly measure and examine how each part of the circuits work. They aren't in any way practical, though, as even the most carefully designed discrete circuit will be miles behind the performance of an IC, be much more expensive, and require many hours of work to implement.

One of the key aspects of ICs is that each and every part can be tuned for specific parameters. Even if you had the time and budget to select 30 different types of transistors and use only the most precise resistors for your discrete design, you couldn't manage the kind of matching and customization possible on a silicon die.

There's a very good book about analog IC design called "Designing Analog Chips". The author, Hans Camenzind, has made it available for free here:

In it, you'll see a LOT of interesting methods that aren't possible in discrete designs, like using a BJT with 50 emitters. It also explores the numerous problems inherent in getting consistent performance from a circuit.

There's a huge world of things to learn about opamp design, and discrete circuits are a good place to start. Just don't expect to get any "magic" out of them compared to their IC cousins.

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