Zen Variations 7 — Nelson Pass / 2004

One of the performance issues raised by the original Son of Zen (Audio Electronics, #2, 1997) was its efficiency figure, which was charitably described as 4% (500 watts in, 20 watts out). You may recall that this was dictated by the original requirements - no feedback, no capacitors in the signal path, and a single gain stage. Zen Variation 6 relaxed the requirements on feedback and capacitors in order to provide a tutorial exercise about “super-symmetric” feedback. The performance was improved in distortion and output impedance, but the efficiency was only slightly improved, largely because we used most of the… 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...