Pass Laboratories, Inc. was founded in 1991 by Nelson Pass. Operating out of his shop at home, Pass developed prototypes of a single-ended Class A amplifier design. At the same time, he and Mike Burley were constructing an in-house machine shop with three home-built CNC milling machines with which to produce the amplifiers when the design was finished.

The first product, the Aleph 0, shipped in 1992. It was a mono-block design rated at 70 watts into 8 ohms, and was unique in using three gain stages of power Mosfets including a push-pull output stage biased by a big constant current source. The amplifier operated as single-ended Class A up to its 70 watt rating and in push pull Class A at higher wattage.

The amplifier was highly acclaimed, and was called the “Amplifier of the Decade” in Stereophile magazine.

At this time, Nelson hired his next-door neighbor, Elena Tong, to help with producing the amplifiers, and she manages much of the company to this day.

A stereo version called the Aleph 0s followed after, along with a preamp called the Aleph P. A larger version of the Aleph 0 called the Aleph 1 shipped the following year, and was a mono-block rated at 150 watts.

In 1994 Pass Labs released a newer Aleph design which simplified the circuit from three gain stages down to only two stages and used a newly patented power current source to bias the single-ended output stage. The new circuitry was incorporated into a revision of the Aleph 1, the 200 watt Aleph 1.2, and smaller models, the 100 watt Aleph 2.

In 1994 Nelson was joined by Wayne Colburn, who began working on improved version of the preamp and on a new phono stage. The company received two patents this year, one of them the design that became the SuperSymmetric circuit in use today.

In 1995, the 30 watt Aleph 3 and Aleph L preamp were released. Also in 1995 the Joseph Sammut left his position at Krell and became operations chief at Pass labs. The following year he was followed by designer Desmond Harrington.

In 1997 Wayne Colburn’s efforts bore fruit in the revised Aleph P, the Aleph Ono phono stage, and the D1 digital to analog converter.

By 1995 the company had outgrown Nelson’s buildings, and a building was begun in a new location. In 1997 Pass Labs moved out of Nelson’s shop space and into a new facility in Foresthill. By then, even more space was needed, and was leased for storage elsewhere. Nelson’s original shop continues to house research.

In 1998 the company released the X1000, the first amplifier using the patented SuperSymmetric topology. The X1000 achieved 1000 watts with high performance, local feedback and only two gain stages: a cascoded differential pair of transistors and a large bank of complementary output followers. This ground breaking design has formed the amplifier products from Pass Labs to the present day.

The X1000 also introduced Desmond Harrington’s signature mechanical design work. The X1000 was followed by the mono-block X600, the stereo X350, and the stereo X250 and X150 models.

In 1998 and 1999, Wayne’s preamplifiers X0, X1, and Xono were released, and Joe Sammut became the President of Pass Labs, freeing Nelson to devote all his time to product.

In 2001 Pass Labs shipped the XVR1 active crossover and X2.5 preamplifier.

In 2002 the first XA amplifiers were released, combining the X and Aleph topologies into balanced single-ended Class A amplifiers with many of the characteristics of both the X and Aleph series. The XA200 was rated at 200 watts mono, the XA160 was 160 watts.

In 2003 the company produced the X150.5, the first major improvement of the X150 amplifier, and followed it with “.5” revisions to the other X amplifiers through 2003 and 2005.

In 2007 Pass Labs is applying the “.5” advances to the XA series of amplifiers, with the XA100.5, XA60.6, and XA30.5 shipping as of this writing. These revisions dramatically lower distortion and noise and also dramatically improved the performance of the amplifiers into low impedance loads.

Also in 2007, Desmond Harrington assumed responsibility as President of the company. Nelson and Wayne continue development work, Joe manages sales and marketing, and Elena and Kent English manage the rest of the company. All these people still like each other, and sit in the same office everyday. This way they can all can hear everything that’s going on, laughing about most of it.