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Death of Zen (DoZ) – A New Class-A Power Amp

Death of Zen (DoZ) – A New Class-A Power Amp

The Zen – along with Zen improved, son of Zen, Bride of Zen, Second cousin of Zen (or did I imagine that one?) Class-A amp designed by Nelson Pass seems to have become popular.
Introduction

The Zen – along with Zen improved, son of Zen, Bride of Zen, Second cousin of Zen (or did I imagine that one?) Class-A amp designed by Nelson Pass seems to have become popular. (See references.) I cannot imagine why, since the very concept is flawed in many ways. It has minimal feedback, but that is because it has minimal gain to start with, and appears very simple. Perhaps this is the attraction – but at what price? The capacitors needed for the power supply are massive to try to get rid of hum, and massive means expensive. The “improved” Zen is a little better, since it uses an inductor (or choke) in the supply – obviously the hum drove someone mad. Inductors are expensive too, and also hard to get, and the capacitance has been doubled in at least one version I have seen – ouch, this is seriously expensive!

Well, actually I can see why it is popular. It satisfies the requirement of many amplifier builders, in that it is simple, stable, and very tolerant of layout and component variations. The sonic characteristics will also appeal to many, due to the valve-like sound (or tube-like, if you prefer). Having looked at the original and many of the “improvements” currently on the web, I did a few tests of my own and frankly, found the amp lacking in the fidelity department. Hi-Fi this most certainly is not. But …. does it sound good? Apparently so, based on the number of people using (and praising) the Zen, but the feedback I have had on the DoZ so far (and my tests) is also very positive and encouraging. At the time of writing, hundreds of DoZ amplifiers have been made, with comparatively few reported problems. The issues that have been encountered have been addressed in the Revision-A circuit boards which are now shipping.

Nelson Pass quotes Einstein as saying “Everything should be as simple as possible, but no simpler”. I agree with this entirely, and quickly realised that the Zen is simpler than it should be for its intended purpose.

Therefore, I have done some serious work on “Death of Zen”, a new Class-A power amplifier that will blow the Zen and all its kin into the weeds, without busting the budget or sacrificing sound quality. Minimal global feedback and lots of local feedback to ensure a very fast and linear amplifier, using the smallest number of components possible. This is the goal, and the remainder of this section explains why.

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