Pass Labs Xs-150 and Xs-300 Mono Amplifiers

Pass Labs announced a new generation of audiophile-grade Xs Series amps, starting with the 150-watt Xs-150 and 300-watt Xs-300 mono power amplifiers, claiming to drive any load from any source.

The new amps are designed to measure well objectively and, equally important, sound subjectively as well as they measure, an exacting engineering challenge that has led to a multitude of ear-pleasing refinements. Pass Labs’ new enhancements further narrow the gap between what scientific measurements report about amplifier performance and what the human ear subjectively hears.

The Xs-300 and Xs-150 Amplifiers are mono block models, both of which offer double-stacked chassis with the power supply and current source in one chassis and the input and main output stage in the other chassis. The separate power supplies enable a bounty of benefits, including lower electromagnetic noise, twice as much storage capacitance as earlier Pass Labs amps, banks of high-speed/soft-recovery rectifiers, improved high-frequency noise filters, bigger and better transformers, improved passive decoupling, massive heat sinks, and lower standby currents.

The Xs Series has been three years in development. The first year, Pass Labs settled on the power supply and physical package. The second year, Pass Labs finalized the output stage and front end. The third year, the company refined the front end and the biasing of the output stage.

In the process, Pass Labs applied a number of new refinements, including adjusting the values for push-pull Class A biasing and the amount of single-ended bias in the output stage. It also significantly increased the single-ended bias in the output stage over earlier Pass Labs amplifiers. All three changes delivered major improvements. Pass Labs also installed sturdy output stage transistors, with a combined capacity well over 10 KW, and massive heat sink assemblies capable of 2 KW all day long.

Features

• Separate chassis for lower electromagnetic noise
• Power supplies with greatly enhanced storage capacitance
• Banks of redundantly parallel high speed / soft recovery rectifiers
• Improved high frequency noise filters
• Larger / quieter transformers
• Improved passive decoupling
• Lower power standby
• Input impedances of 200 k-ohm balanced with negligible capacitance

Price and Availability

• Pass Labs Xs-150 → $65,000/pair (available Q1 2012)
• Pass Labs Xs-300 → $85,000/pair (available Q1 2012)