Op-Amp Cookbook Part 4 Meets Modern Innovation: Precision Instrumentation and Test Circuits Reimagined

Revisiting Ray Marston’s Classic Analog Designs Through a Modern Lens

In Part 4 of Ray Marston’s Op-Amp Cookbook, the spotlight turns to instrumentation and test-gear circuits—power supplies, reference generators, and low-drift amplifiers that form the backbone of precision analog design. First published in Nuts & Volts in 2001, these designs showcase the versatility of the then-ubiquitous 741 op-amp.

Today, these same circuit principles remain essential. By pairing timeless architectures with Linear Systems’ ultra-low-noise JFETs, designers can achieve cleaner signals, more stable outputs, and more efficient performance in modern applications.

Classic Circuits: From Variable Supplies to Overload Protection

Marston introduced a series of clever instrumentation designs, including:

• A variable 3–15 V power supply: Built around the 741 op-amp, with a Zener-based 3 V reference and gain control via potentiometer.

• A power-boosted version: Using Darlington emitter followers to deliver higher current capability.

• An auto-protected design: Adding automatic overload detection to safeguard both circuit and load.

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These simple but powerful concepts highlighted how feedback, gain control, and reference generation can be combined into reliable analog building blocks.

Modern Upgrades with Linear Systems FETs

Where the 741 once reigned, today’s precision circuits can benefit from Linear Systems’ advanced JFET portfolio.

Design Challenge	Modern Solution with Linear Systems Devices
Noise and Drift	Devices like the LSK170 and LSK389 deliver industry-leading low noise and thermal stability, ensuring clean and reliable voltage rails.
Temperature Stability	Thermally matched dual JFETs maintain consistent gain across varying conditions—critical for calibration, sensing, and test gear.
Efficiency and Footprint	FET-based current stages can replace bulky Darlington pairs, reducing heat dissipation and improving efficiency.
Fine-Grained Control	Wide IDSS binning and flexible packaging make bias networks easier to optimize for modern compact designs.

A Real-World Example

Imagine updating Marston’s variable power supply with a Linear Systems FET front-end:

• Use an LSK170 to generate a clean, stable reference input.

• Pair it with a precision modern op-amp for ultra-low drift regulation.

• Replace Darlington emitter followers with a FET-based pass element, yielding higher output current in a smaller footprint.

• Add smart overload protection using FET-based sensing for safe, reliable operation.

  
  

The result? A compact, efficient precision supply that outperforms the original while staying true to its elegant design.

Why These Designs Still Matter

• Fundamentals endure: The principles of feedback, reference control, and gain remain cornerstones of analog design.

• Versatility: Precision power supplies and test circuits are still indispensable in labs, sensing systems, and instrumentation.

• Performance gains: Modern JFETs unlock stability, noise reduction, and efficiency that weren’t possible when the Cookbook was first written.

Closing the Cookbook

As we wrap up this four-part series revisiting Ray Marston’s Op-Amp Cookbook, it’s clear that analog design remains as relevant as ever. Classic circuits provide the blueprint, but Linear Systems devices transform them into high-performance solutions for today’s designers.

Whether you’re building test gear, reference supplies, or precision measurement tools, our low-noise JFETs—like the LSK170 and LSK389—deliver the accuracy and reliability modern innovation demands.

👉 Explore our product portfolio here and discover how Linear Systems can power your next design.