🔧 Dive into Precision: The All-JFET Differential Amplifier

At Linear Integrated Systems, we’re passionate about crafting the world’s highest performance discrete semiconductors. Today, we’re excited to spotlight an advanced design that exemplifies the exceptional performance of our JFET products: the All-JFET Differential Amplifier.

⚙️ The Heart of the Design

This amplifier circuit, built entirely around JFETs, demonstrates how carefully selected and matched components can create an ultra-low-noise, highly linear amplification stage. Let’s take a closer look at the core building blocks:

🔹 Differential Input Stage

The amplifier begins with a balanced differential pair:

• Q1A/Q1B (LSK489): Monolithic dual N-channel JFETs

• Q2A/Q2B (LSJ689): Complementary dual P-channel JFETs

  
  

  These matched pairs ensure symmetrical operation, significantly reducing offset voltages and maximizing common-mode noise rejection (CMRR).

🔹 Biasing and Current Mirrors

Using precision current sources and mirrors, the amplifier achieves rock-solid biasing. This stability is key to delivering consistent gain, minimal distortion, and a clean audio path across temperature swings.

🔹 Push-Pull Output Stage

The output section features pairs of LSK170B and LSJ74A JFETs. These push-pull stages combine to provide:

• Excellent linearity

• Low output impedance

• Ability to drive demanding loads, while maintaining the sonic signature of JFETs

🔹 LED Biasing and Decoupling

LEDs are cleverly used to stabilize bias points while keeping the amplifier quiet and responsive. Careful capacitor decoupling throughout the circuit ensures that no unwanted noise seeps into the signal path.

🎧 Why Use an All-JFET Amplifier?

✅ Ultra-Low Noise

Our JFETs have some of the lowest noise figures in the industry—ideal for high-end audio, test & measurement, and sensor applications.

✅ High Linearity

JFETs’ square-law characteristics deliver sweet, natural-sounding linearity that’s prized in audiophile-grade equipment.

✅ Common-Mode Noise Rejection

Thanks to the differential topology, this amplifier can reject noise that affects both input lines equally—perfect for instrumentation and precision audio.

✅ Reliability & Thermal Stability

Matched pairs like the LSK489 and LSJ689 maintain consistent performance across temperature variations, ensuring your design stays rock-solid.

🔬 Applications in the Real World

From audio preamplifiers in recording studios to sensor front-ends in medical equipment and aerospace systems, this all-JFET differential amplifier topology ensures performance that professionals rely on.

This diagram showcases how Linear Integrated Systems’ JFETs—like the LSK489, LSJ689, LSJ74A, and LSK170B—work together to create an amplifier that excels in sonic purity and technical performance.

💡 Ready to Build or Learn More?

If you’re designing a precision amplifier or want to see how our JFETs can elevate your next project, get in touch!

Visit www.linearsystems.com to stay updated on the latest application notes, product releases, and technical insights.