Bride of Zen — Nelson Pass / 1994

This is the second installment of a trilogy of construction projects centered around the performance obtainable from absolutely minimalist circuitry. Part one described the Zen amplifier, a 10 watt single-ended class A power amplifier using a single MOSFET gain stage. In this piece we will examine its preamplifying mate, also a single gain stage MOSFET circuit. A lot of what I might say about this design has already been expressed in the Zen amplifier piece, and will not be repeated here. It is enough to say that I continue to be very intrigued by the sound of very simple topologies,… More...

Current Source Crossover Filters — Nelson Pass / 2004

In today’s marketplace, audio power amplifiers are conventionally viewed as voltage sources, delivering a given voltage at the output that is a multiple of an input voltage. To the extent that they are truly voltage sources, having a very low output impedance, they simply deliver whatever current happens to reflect the response of the loudspeaker to the defined output voltage. Recently I have been playing with current source power amplifiers that have high output impedances and deliver a specific current to the load in response to an input voltage. The voltage across the loudspeaker reflects its response to this defined… More...