The Willow Pre-amp: A high slew-rate JFET amplifier

January 17 2015, 18:00
This project, originally published by audioXpress in December 2011, has been the topic of much discussion, updates and follow-up projects, so much so that we decided to make it available online. To understand the project there’s nothing better than to read what the author, Robert Nance Dee, wrote about it in the introduction.

“The curious thing about specifications is that there are none for musicality. I love the single-ended tube builders who stick to their guns about the musicality of Class A amps that run into single-digit distortion. Musicality must be paramount!

"The first specification I always place a few notches down on the criteria list is distortion. Quite frankly, no one on the planet can hear the difference between 0.01 and 0.005 distortion. In fact, once you get under about 0.5%, if that, distortion is a non sequitur. What really counts to my ears is tracking, which I pay close attention to when I begin the design process.

"I always go for high slew rates because they bring clarity and definition to amps. My hat goes off to designers such as MOON who list slew rates in their specs.
"Willow is just that type of project. The PMBF4393 JFET has a rise time of 5 V/ns (200 V/μs), and the people who have listened to this amp can hear the difference. I built it as a companion to my 5002 power amp, both using the HA5002 buffer.”

Read the full article here
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