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...

Arch Nemesis — Nelson Pass / 2010

A poster of Einstein once said, “Things should be made a simple as possible, but no simpler”. This can apply to audio amplifiers, but if they are evaluated subjectively, the simplicity thing can get a little of of hand. Of itself, minimalism exerts a strong aesthetic attraction, and there is a reasonable belief that fewer components in the signal path allows more information to get through with less coloration. If like me you are interested in understanding of how we hear distortions with our brains (instead of our meters), you might appreciate that simple circuits help isolate these phenomena. I… More...