About Pass DIY

Nelson Pass has been an early contributor to the audio DIY scene; It has been said that Nelson has a knack of explaining engineering things very clearly in a few words, and that he obviously enjoys doing it. He is also a very active contributor at www.diyaudio.com. Being very generous with advice, tips, and complete amplifier designs that people can build.

What does Nelson Pass get out of this interaction?

“I like to speak to the teenager (me) who wanted to know this stuff—that's my audience. There are always people who appreciate a decent explanation that gets to the meat and potatoes. I see it all as light entertainment with a little education thrown in. The academic paper approach has its place, but it seems intended for people who mostly understand the stuff already. If you want to communicate with DIYers, you depend more on colorful analogies, a little hand waving, and very little  differential calculus. I get lots of personal satisfaction out of the whole enterprise. It gives me an outlet for some cool ideas and things that otherwise would stay bottled up, and I have an excuse to explore offbeat approaches purely for their entertainment value. Also, the process of communicating DIY stuff is a two way street—I would say I get about as much as I give. Nelson Pass”

Super-Symmetric Amplification — Nelson Pass / 1998

U.S. Patent # 5376899 describes a new amplifying circuit topology that takes advantage of the character of special matched balanced amplifiers that are cross-coupled to provide cancellation of distortion and noise. The result provides high performance with very simple linear circuits, better than previous efforts by an order of magnitude. We have dubbed the approach Super-Symmetry (Su-Sy), an homage to particle physics. Super-Symmetry works by exploiting the complementary characteristics of precision matched balanced circuits to differentially reject distortion and noise, and extends this symmetry to make the distortion and noise virtually identical on each half of a balanced amplifying circuit.… 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...

The Pass A-40 Power Amplifier — Nelson Pass / 2000

FLATTERED BY THE opportunity to publish a project circuit, the designer is often beset by seemingly contradictory considerations. On the one hand, it is tempting to design a complex circuit as a demonstration of technical prowess; an amplifier with large numbers of esoteric components performing obscure functions. Such an amplifier might be a smorgasbord of electronic technique, featuring class A operation, cascoding, constant current sources, current mirrors, and extra-loop error correction. It would be fascinating to build and perhaps would also sound good. On the other hand, complexity is not a good end in itself and a much simpler circuit… More...

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