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...

The Pass A-40 Power Amplifier — Nelson Pass / 2000

FLATTERED BY THE opportunity to publish a project circuit, the designer is often beset by seemingly contradictory considerations. On the one hand, it is tempting to design a complex circuit as a demonstration of technical prowess; an amplifier with large numbers of esoteric components performing obscure functions. Such an amplifier might be a smorgasbord of electronic technique, featuring class A operation, cascoding, constant current sources, current mirrors, and extra-loop error correction. It would be fascinating to build and perhaps would also sound good. On the other hand, complexity is not a good end in itself and a much simpler circuit… More...