The History of Threshold
Threshold Audio was established in California in 1974 by audio engineer Nelson Pass and graphic designer Rene Besne. The company is well-known as a high-end audio equipment manufacturer today.
In the early 1970s, Nelson Pass was studying Physics at the University of California-Davis. While a student, he founded PMA to design and manufacture speakers. In 1972, he joined ESS speakers in Sacramento just prior to the arrival of Oscar Heil, who would design the Heil Air Motion Transformer which was a key component of the ESS AMT series of speakers. Pass worked at ESS designing crossovers and enclosures through 1973. He also was a service manager for Sun Stereo performing repairs on McIntosh Laboratory, Phase Linear, Pioneer Corporation and other brands of amplifiers, and began formulating his own amplifier designs in 1974. Pass received his Bachelor of Science in Physics and with an ESS associate René Besne they together began development of a new amplifier in 1974. Besne worked on the industrial design of the amplifier while Pass worked on the circuit topology and component selection. When they were confident the amplifier was ready to market, Pass and Besne incorporated Threshold as co-founders in Sacramento, California on December 5, 1974.
The first amplifier sold by Threshold was the model 800A, introduced in early 1975. This was a Class A 200 watt per channel five-stage amplifier with triple series/triple parallel/triple Darlington output stage with a dynamic bias circuit. During development of the 800A, Pass and Besne met Joe Sammut, who later became a business partner in Threshold. The second amplifier offered some months later was the 400A which featured 100 watts per channel. Threshold also released the NS 10 pre-amplifier in 1977.
The heart of Pass's designs around ths time formed what would later be codified as the STASIS topology: "Single or dual channel, non-phase inverting audio power amplifier employing circuitry to suppress voltage and current variation and enable performance to be dominated by a system maintained in a stasis condition of constant voltage/constant current, linear state operation. No overall negative feedback is employed around the amplifier system. No output protection circuits are utilized. Active constant current sourcing is employed at every gain stage. Power is sourced through a one kilowatt transformer and greater than a 70k microfarads capacitance."
The Threshold amplifiers drew the attention of audiophiles and editors at audio equipment magazines. In the late 1970s, Pass further developed his amplifier technology and Threshold began to market the STASIS line of amplifiers. This served as the basis of Threshold’s amplifier line throughout the 1980s. Pass was quoted as saying, “The Stasis 1 was the statement product for what became the popular Stasis product line, which served Threshold for the life of the company.” In another interview, he stated: “The Stasis amplifier certainly stands out as probably the premier example of a simple, creative topology that’s done a very good job and stood the test of time.” Virtually all Threshold amplifiers and pre-amplifiers displayed a luxurious look of "sculptured" brushed aluminum faceplates that were Besne's hallmarks of the entire line in keeping with the components’ substantial price. Some of the equipment was offered in black or clear (silver) anodized finish as well. In 1985 the Japanese audio company Nakamichi contacted Threshold to lease a patent license for the Stasis technology and consult with Nelson Pass, in order to design and market a few high-end stasis amplifiers. The resulting Nakamichi PA-5, PA-7 and PA-7 series II amplifiers was sold successfully for several years as well as a few Nakamichi receivers also utilizing amplifier sections utilizing Stasis technology.
An extensive interview with Nelson Pass was publilshed in the November 1991 issue of Stereophile. Mr. Pass left Threshold at the end of 1991 to establish Pass Labs, hoping to have more autonomy in his amplifier design. Besne also left the firm shortly thereafter.
Threshold ceased operations in the mid-90's. The intellectual property was sold in the early aughts, and the brand exists today as "Threshold Audio."