A75 Part 2 — Norman Thagard & Nelson Pass / 1992

THE STORY BEHIND the A75 power amplifier continues. In Part I, we discussed its origins and direct predecessor, the Pass A40, as well as some general guidelines to follow before initiating such a project. We covered such topics as MOSFETs and differential pairs. In this concluding part, we will analyze the amplifier's component parts in depth, beginning with the source. The Power Supply Figure 11 shows the amplifier's power supply circuitry. AC line power enters through the power cord and passes through fuse F1. To reduce the effects of inrush current, thermistor TH1 is employed. At room temperature, this will… More...

Audio, Distortion and Feedback — Nelson Pass / 2008

Audiophiles seem to revel in minor controversies – vinyl vs CD's, tubes versus solid state, capacitor, wires, magic dots... and negative feedback. At one extreme, the position is that “feedback makes amplifiers perfect”. At the other extreme, “feedback is a menacing succubus that sucks the life out of the music, leaving a dried husk, devoid of soul”. The former viewpoint usually belongs to so-called “objectivists” who have a fine appreciation for electronic theory and measurements. Their opposites would be the “subjectivists” who emphasize the listening experience and often own tube amplifiers. Accusations are occasionally made that objectivists can't hear, and… More...