Pass Labs' new Concept Amplifiers are high-bias, Class A, monoblock models employing the company's ultra-symmetry circuit. Originally designed by Nelson Pass for use at his own retreat, they were shown in "concept" form at the 2010 CES.

They are like large versions of the company's flagship XA200.5 Amplifier, notable for its high output capacity, power and stability. Like the XA200.5, they deliver music without straining, and possess twice as much chassis, power supply, output stage and dissipation capacity.

Additional Resources
• Read more amplifier news from HomeTheaterReview.com.
• Find a receiver to pair with Pass Labs' Concept Amps.

The Concept Amps are available in large and smaller models. The large amp delivers about 300 watts, and is equivalent to two XA200.5-size chassis per side (four for stereo). The smaller model delivers about 200 watts, and is equivalent to two XA160.5 Amp chassis per side (four for stereo). Each includes a separate power supply.

The Concept Amps feature the same output stage topology as the XA200.5 with twice as much heat sink, more output devices (currently 144), and a push-pull bias up to 300 watts (600-watt peak) into 8 ohms. New bias hardware increases the Concept Amps' single-ended Class A bias from the XA200.5 Amp's 5 watts to over 300. The Concept Amps' front end circuits are also biased higher, with the JFET input stage bias triple that for the XA200.5 Amp, and the voltage amplification stage bias quintuple that of the XA200.5.

The Concept Amps' gain circuits operate with less feedback and degeneration than previous designs to deliver a more relaxed liquid quality while maintaining high power and control into difficult loads.

Suggested prices for the Concept Amps are approximately $70,000/pair for the large model and approximately $45,000/pair for the smaller model.