Nelson Pass
Encyclopedia
Nelson Pass is a noted and widely respected designer of audio amplifier
Audio amplifier
An audio amplifier is an electronic amplifier that amplifies low-power audio signals to a level suitable for driving loudspeakers and is the final stage in a typical audio playback chain.The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification,...

s.

Unlike some audio engineers, Pass remains vocal that listening tests remain valuable and that electrical measurements alone do not fully characterize the sound of an amplifier.

Mr. Pass holds at least seven U.S. patents related to audio circuits.

Studies, PMA and ESS

1974 he received his BS in physics from the University of
California-Davis.
During his studies he and Mike Maher founded the small speaker
company PMA. From 1973 to 1974 he was employed at ESS to design speakers.

Threshold

After graduating in 1974 he and René Besne founded high-end amplifier company Threshold Electronics on December 5, 1974. Later Joe Sammut became the third partner. Threshold is perhaps best known for the "Stasis" amplifiers (a design later also produced under license by Nakamichi
Nakamichi
is an historic Japanese high end audio company most famous for its innovative and very high quality audio cassette decks.In 1972, Nakamichi launched its first Nakamichi-brand products, home audio gear that included the world's first three-head cassette deck...

). He sold Threshold Electronics in 1997.
The company continued without Nelson Pass under the name Threshold-Audio.

Pass Labs

Pass founded Pass Labs
Pass Labs
Pass Labs is a high end audio company based in Foresthill, California, USA founded by Nelson Pass, a well known figure in the high end audio community. Pass is known for unique and innovative, as well as practical, circuit designs....

 in 1991. For many years a notable and highly regarded design / product by Pass (and his companies) was the Class A "Aleph" series of single ended amplifiers. Pass Labs produces the powerful and highly regarded X series amplifiers, which make use of the "supersymmetry
Supersymmetry
In particle physics, supersymmetry is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners...

" topology patented by Pass, to give extremely low distortion levels, and more recently the XA series of amplifiers, which advantageously combines aspects of the Aleph design with the supersymmetry technique.
Recently Pass Labs has introduced a loudspeaker, and Pass DIY has increasingly explored the field of high efficiency / full range speakers as a complement to minimalist amplifier designs.

First Watt

In parallel with Pass Labs
Pass Labs
Pass Labs is a high end audio company based in Foresthill, California, USA founded by Nelson Pass, a well known figure in the high end audio community. Pass is known for unique and innovative, as well as practical, circuit designs....

, Pass also runs First Watt, a self described "kitchen table" commercial venture where Pass hand builds (in very limited numbers) some low power / minimalist designs he chooses to not series produce through Pass Labs.

DIY

Unusually for a leading figure producing commercial equipment, Pass has also long been very supportive of the DIY audio
DIY audio
DIY Audio means "do it yourself" audio. Rather than buying a piece of possibly expensive audio equipment, such as a high-end audio amplifier or speaker, the person practicing DIY Audio will make it him/herself...

 community, by way of published articles (Notably in "The Audio Amateur") and schematics of out of production models on the Pass Labs site and more recently the First Watt site. Unusually for such a noted figure, he frequently interacts directly (if tersely) with audio hobbyists individually, all of whom are extremely grateful. His nickname among the DIY audio community is "Papa".

Pass' Design Characteristics

Typically using MOSFETs as the gain devices, (often as current sources rather than voltage sources), most of his designs operate in Class A, with all the low distortion of small signal benefits generally associated with that. He is also known for his advocacy of "minimalist" designs which reduce the circuit complexity / number of components through which the audio signal must travel, resulting in any residual distortion having a very simple distortion spectra. His more powerful designs that go beyond what can practically be realized in Class A (such as the Threshold and Pass Labs products) operate in Class AB1 but retain a heavy bias so that they operate in Class A during quieter passages, and great emphasis has been given to avoiding / minimizing switching effects (e.g. the Stasis concept)
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