Nelson Pass spent years experimenting with Static Induction Transistor devices in his low-power First Watt designs before the technique found its way into something considerably more ambitious - the Pass Labs Xs150, a monoblock that captures what the company calls the SIT device's "unique tube-like sonic footprint" from a much higher-output MOSFET circuit.Hifiverse's own Munich 2025 verdict, "the bass is deep, powerful and controlled, does not clog the rest of the frequencies," is precisely the kind of result that circuit-level engineering was chasing.
The system at a glance
One component, a flagship 150-watt-per-channel Class A monoblock pair from Pass Laboratories' top-tier Xs range, and a price around $120,000 to $136,000 depending on market and finish. The amplifier alone is the subject of this Munich entry, spotlighted from the show floor rather than documented alongside a full multi-brand system.
Why these components work together
The Xs150 delivers its 150 watts per channel into 8 ohms entirely in Class A operation, using 112 output devices per channel and drawing 700 watts continuously regardless of the music playing, a substantial power-supply commitment for a monoblock rated at what looks like a modest wattage figure on paper. That approach traces directly back to founder Nelson Pass's years of SIT experimentation in his First Watt side-projects - instead of simply scaling up a conventional MOSFET output stage for more power, the Xs series circuit modification specifically aims to reproduce the particular tonal character SIT devices deliver at low power, but from devices capable of the higher current a demanding loudspeaker load requires. The amplifier's two-chassis construction, separating each monoblock's circuitry from its power supply, minimises electromagnetic interference between the two sections, while enhanced storage capacitance and redundant, parallel high-speed rectifiers keep that substantial Class A current delivery clean under sustained demand, exactly the kind of engineering that translates into controlled bass response regardless of how demanding the connected loudspeaker's impedance curve happens to be.
How it sounds
Hifiverse's own show-floor assessment, deep, powerful and controlled bass that doesn't clog the rest of the frequency range, reflects what Class A operation with this level of power-supply reserve is engineered to deliver - bass output that stays separate and well-defined instead of smearing into the midrange the way amplifiers running out of current reserve under heavy bass demand often do.
1 component
- Power amplifiers mono
XS150
by Pass Labs
Pass Labs XS150 followed by deployment in Nelson's First Watt designs, circuit modification captured the unique tube-like sonic footprint of SITs from much higher-output MOSFET devices used in the Xs series.