Single Ended Class A — Nelson Pass / 1995

Single-Ended Class A amplifiers have certainly hit it big in the four years since we began testing the first Aleph 0. So is this just another audio fad, or is there something fundamental about this kind of design, justifying a revival of the old approaches to amplification? When I started designing amplifiers twenty-five years ago, solid state amplifiers had just achieved a firm grasp on the market. Power and harmonic distortion numbers were the important thing, and the largest audio magazine said that amplifiers with the same specs sounded the same. We have heard Triodes, Pentodes, Bipolar, VFET, Mosfet, TFET… More...

Zen Variations 1 — Nelson Pass / 2001

As an exploration into the potential performance of a very simple amplifier, the Zen amplifier has succeeded in creating notoriety and some controversy over the last 8 years. More importantly, it's novel and simple construction appears to have encouraged a large number of doit- yourselfers to take up a soldering iron and jump in. Having only a single gain device, the design's name is a pun on the Zen Koan, "What is the sound of one hand clapping?", but the point is quite serious. High quality sound can be obtained with simple and accessible circuits. Conversely, it is quite easy… More...