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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.

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.

Read more about the history of Pass Labs here.