Pass Labs
Founded in 1991 by Nelson Pass, this American high-end amplifier manufacturer focuses on MOSFET-based Class A/AB designs pursuing simple, natural sound quality. While measurement data is good, their designs involve significant power consumption and heat generation, lacking rationality by modern standards. Cost-performance is extremely poor compared to latest high-performance Class D amplifiers. Despite high corporate reliability, the technology is largely outdated with strong obsolete aspects, making evaluation difficult from modern engineering perspectives.
Overview
Founded in 1991 by Nelson Pass in California, this high-end amplifier manufacturer draws from Pass’s experience as president of Threshold Corporation since 1974, with over 20 years of innovative circuit design including Improved Class A Stasis circuits. Pass studied physics at University of California and holds numerous amplifier design patents.
Current development staff are all music enthusiasts working under Nelson’s supervision to ideally realize “what should be heard and what should not be heard.” The design philosophy provides simple, natural characteristics, implementing this through MOSFET-based X series, XA series, and XS series. The annual “Nelson Pass Amp and Speaker Camp” held in Sebastopol, California continues to grow in popularity.
Scientific Validity
\[\Large \text{0.7}\]Pass Labs products publish measurement data with no unscientific claims, which is commendable. The XA25 achieves 0.01% THD+N at 25W/50W (8/4Ω), while the XA60.8 realizes THD below 0.1% at 8Ω load. However, the XA60.8’s S/N ratio of approximately 80.9dB (wideband) is practically adequate but clearly inferior to the 110dB+ values achieved by latest high-performance Class D amplifiers. While claimed performance is data-supported, some important metrics fall short of contemporary standards, limiting the score.
Technology Level
\[\Large \text{0.3}\]Nelson Pass’s circuit design received some recognition from the 1970s to 1990s, but is clearly outdated by modern technological standards. The company’s Class A/AB amplifier technology is fundamentally inferior compared to latest Class D amplifier technology. For example, latest Class D amplifier modules like Hypex NCx500 and Purifi 1ET9040SA achieve vastly superior THD+N (below 0.0003%), S/N ratio (above 120dB), and power efficiency (above 90%) compared to Pass Labs’ Class A amplifiers. The XA60.8’s S/N ratio of 80.9dB is clearly inadequate by contemporary standards. The simple circuit configuration using MOSFETs is now merely adherence to obsolete technology. From the latest technological standards, the company’s technology significantly falls below industry average, with no technical superiority whatsoever.
Cost-Performance
\[\Large \text{0.0}\]The XA25 (USD 4,867) delivers 25W/8Ω at 0.01% THD, but the Fosi Audio V3 (approximately USD 133) achieves equivalent or superior output at lower distortion rates. Performance-to-price ratio is USD 133 ÷ USD 4,867 ≈ 0.03, resulting in a 0.0 score per review policy. Similarly, XA60.8 monaural pairs (USD 15,400, 60W/8Ω) and X250.8 (USD 9,333, 250W/8Ω) cost 10+ times more than Topping or Hypex NCx500-based Class D amplifiers (USD 667-1,333 range) for equivalent measurement performance. The Topping PA7 Plus (pair approximately USD 933) shows superior measured values to the XA60.8. When evaluating pure performance-to-cost, numerous products exist at 1/10th the price with equivalent or superior performance, resulting in the lowest cost-performance rating.
Reliability & Support
\[\Large \text{0.9}\]Operating continuously for over 30 years since 1991 founding, corporate reliability is extremely high. With founder Nelson Pass still central to design, technical consistency is maintained. In Japan, Electori Co., Ltd. provides comprehensive support as authorized distributor, offering up to 5-year warranty on the XA60.8 and complete after-sales service. Product construction is robust, with sustained high prices in used markets proving long-term reliability. Nelson Pass’s engineering passion and corporate stability ensure long-term support expectations.
Rationality of Design Philosophy
\[\Large \text{0.5}\]While the “simple, natural characteristics” design philosophy is consistent, the fixation on Class A operation as means raises rationality questions from modern engineering perspectives. Class A operation theoretically eliminates crossover distortion but requires extremely low power efficiency with massive heat generation and large chassis requirements. Given that latest Class D amplifiers achieve equivalent or superior low-distortion performance at vastly higher efficiency, Class A adoption cannot be considered rational. While the measurement data emphasis is scientific, the neglect of energy efficiency as an important metric necessitates score reduction.
Advice
Pass Labs is a reliable high-end amplifier manufacturer balancing technical completion with corporate stability. Products like XA25 and XA60.8 remain attractive choices for those who resonate with Nelson Pass’s design philosophy. However, for maximum measurement performance and energy efficiency, numerous alternatives with superior cost-performance exist, including latest Class D amplifiers. Since evaluation varies greatly depending on whether one values brand philosophy and history versus pure performance and efficiency, careful comparative consideration is essential before purchase.
(2025.07.05)