Build a Discrete High Output Current Buffer with JFET Input

This article from Dimitri Danyuk explores ways to provide better isolation between input and output terminals and lower input noise current using JFETs from Linear Integrated Systems. For unity-gain buffer applications there are many open-loop IC buffers on the market based on bipolar technology. They are mostly complementary emitter followers connected in series. With the appearance of complementary JFETs from Linear Integrated Systems, it is possible to construct a discrete buffer with JFET input. This article was originally published in audioXpress, March 2019.

In 2013, Dimitri Danyuk wrote an article that presented apples-to-apples test results for noise densities for several low-noise discrete, SMT, and n-JFETs. In this follow-up article, Danyuk brings us new measurements, updating his design note with measurements of JFET components that appeared more recently on the market. The tests used the same operating conditions so that designers can make a fair comparison for their applications. This article was originally published in audioXpress, December 2018.

This article describes the design and performance of a high-quality DC-coupled all-JFET amplifier. The circuit was inspired by John Curl and Erno Borbely designs and was built with readily available junction-gate field-effect transistor (JFETs) from Linear Systems. The input stage is the the complementary JFET differential pair, the second stage is symmetrical differential amplifier with two pairs of opposite polarity JFETs, and the output stage is a complementary source follower. The amplifier can drive loads up to 150Ω. This article was originally published in audioXpress, October 2017.