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Up for sale is a beautiful Threshold S/150 Series II stereo power amp featuring Nelson Pass’s legendary Stasis topology. This is for those who want something a little smaller than the S/300. I ran both in parallel within my home audio. It enhances any system. Also a conversional piece because people see it and it blows their mind. Original owner. Works as intended. Kept in custom cabinets so handled by very few. Comes with certificate of ownership. Blurred out in photo but very clean. If you are looking at this, you likely already know the pedigree. Unlike later designs that lean toward analytical or dry, the S/150 II strikes a perfect balance. It is incredibly musical, effortless, and sweet - often described as having a tube-like midrange warmth while retaining absolute solid-state authority, grip, and dead-silent backgrounds. It images beautifully and drives difficult speaker loads without breaking a sweat.Specs & Condition:Power: 90 watts per channel into 8 ohms (pure Class A/AB optical bias)Condition: Excellent cosmetic. Faceplate is clean, fins are straight, unmarked, and it performs as it should. The only item that shows some usage is the rubber power inlet but I'll include an extra if you should ever want to replace with exact OEM part. But it works as intended as is. Sound: Warm, coherent, punchy, and fatigue-free. It will make any system sound great. An absolute tank of an amplifier built during Threshold's golden era.I am a fast shipping but this one needs some attention so give me a couple of days to package. Not a store.
Generating expert take…
Threshold Audio emerged in Sacramento, California, in 1974, founded by renowned audio engineer Nelson Pass alongside graphic designer René Besne and Joe Sammut. Pass, a pioneer in amplifier design, launched the brand with the groundbreaking Threshold 800A power amplifier in 1975, introducing a novel sliding bias system that boosted Class A efficiency while employing 48 output transistors in a sophisticated triple-series/triple-parallel configuration. This California-rooted heritage defined Threshold as an innovator during its original run, which spanned until the mid-1990s, after which the intellectual property changed hands, including a 1994 acquisition by investor Randy Patton, who integrated it with PS Audio and relocated operations to Camarillo.
The brand focused squarely on high-end amplification, producing iconic power amplifiers like the 400A and 800A, the Stasis series renowned for their balanced Class A performance, and preamplifiers such as the NS10, SL10, and FET range including the FET-1, FET-2, FET-9, and FET-10. Later designs, like the T-200 by engineer Michael Bladelius, continued this legacy. Threshold eschewed speakers, turntables, DACs, headphones, or cables, concentrating instead on pure analog amplification that prioritized sonic purity and robustness.
Threshold holds a revered position as a vintage high-end icon, cherished by collectors and audiophiles for its enduring sound quality and Pass's technical wizardry. Once a market leader in premium solid-state gear from 1975 to 1992, it remains a sought-after name in the used market, embodying boutique excellence rather than mass production, with modern revivals under Threshold Audio sustaining its elite reputation.
See all Threshold listings on RADAR.
