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...

Zen Variations 5 Hi Res — Nelson Pass / 2003

The Zen Amp concept is an exploration of how well you can make a simple audio amplifier perform. It makes for an interesting illustration of design technique, since more complex circuits are inevitably composed of collections of simple circuits, and it is well recognized that the optimization of these simple sub circuits is usually the key to getting the most out of the larger circuit. Apart from that, there is aesthetic pleasure in rendering a device in a simple way. Also we find that, other things being roughly equal, simple circuits sound better musically. The Zen series has so far… More...