Nelson Pass

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Nelson Pass is a noted and widely respected designer of audio amplifiers^{[citation needed]}.

He received his graduate degree in physics from the University of California-Davis.

During his early career Pass worked at Dynaco, then later at Harmon-Kardon.

He founded high-end amplifier company Threshold Electronics in 1974, perhaps best known for the "Stasis" amplifiers (a design later also produced under licence by Nakamichi). He sold Threshold Electronics in 1987.

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 founded Pass Labs in 1991. Pass labs produces the powerful and highly regarded X series amplifiers^[who?], which make use of the "supersymmetry" 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 supersymetry technique

In parallel with Pass Labs, 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.

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

Unusually for a leading figure producing commercial equipment, Pass has also long been very supportive of the DIY audio community, by way of published articles (Notably in "The Audio Amateur"), and more recently the Pass DIY site. Extremely unusually for such a noted figure,he is readily contactable and frequently interacts directly (if tersely) with audio hobbyists individually : all of which hobbiests are extremely grateful for and for which he is held in very high esteem.^[1] ^[2]^[3]

Typically using MOSFETs as the gain devices, (often as current sources rather than voltage sources), many 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 realised 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 / minimising switching effects (eg the Stasis concept)

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.^[4]

Mr. Pass holds at least seven U.S. patents related to audio circuits.^[5]