Pass Labs Introduces XA.5 Series Power Amplifiers, Designed by Audiophiles for Audiophiles

by Bryan Stanton

Press Release

Numerous Refinements Help 5 New Flagship Models Deliver Improved Power, Control and Performance on Even the Most Demanding Speakers

FORESTHILL, CA, Aug., 2008 — Pass Laboratories, Inc., an audio innovator renowned for its unique high-performance products, has introduced the XA.5 Series Power Amplifiers, its new flagship line of five exceptional amplifiers that deliver greater power, control and performance than any previous Pass Labs models.

Designed by audiophiles for audiophiles, XA.5 Series amplifiers deliver the warmth, sweetness, depth and space that are the hallmarks of fine audio products. They have the power and stability essential to reproducing music without strain, the dynamic range needed for 24-bit recordings, and the ability to retrieve the micro dynamics the most sensitive loudspeakers reproduce. Combining simplicity and power, XA.5 Series amplifiers move easily from total silence to explosive transients without losing information.

The series consists of the 200-Watt XA200.5 Power Amplifier, the 160-Watt XA160.5, the 100-Watt XA100.5, the 60-Watt XA60.5, and the 30-Watt XA30.5. Developed after five years of concentrated research and development, all the new amps embody significant improvements on their classic Pass Labs predecessors. Chief among these improvements are a cascode JFET symmetric front end, single-ended Class A bias, improved push-pull bias circuits, improved output stage topology, more power output devices, bigger power supplies and better circuit layout.

The cascode JFET symmetric front end has less noise, a higher input impedance, and greater linearity. The JFETs operate self-biased in a symmetric quad topology, with each device cascoded and level-shifted to form the full voltage gain stage of the amplifier.

To achieve the single-ended Class A bias, the output stage uses a heavy bias current for push-pull Class A operation to a large portion of the rated power, and has a single-ended bias source for single-ended Class A operation at low wattage. At the same time, a newly developed bias generator eliminates sources of variation in bias current in the output stage, and allows about 20 percent greater power output for a given supply voltage.

The power supplies have greater storage capacitance, larger and quieter power transformers, fast recovery rectifiers, and improved harmonic filtering in both the primary and secondary supply circuits.

The use of more power output devices — specifically, matched complementary power MOSFETs — provides more current and improves power handling and linearity. The XA160.5 and the XA200.5 use 72 output devices per channel, and the smaller amplifiers use a total of 40 output devices. The increased aggregate device capacitance that would slow down large banks of parallel MOSFETS is handled by a unique drive compensation system that dramatically reduces the capacitance, increasing the speed and lowering distortion at high frequencies.

Improving the amplifiers’ layout involved detailed refinement of all portions of each model’s circuitry, achieving lower noise and distortion, and greater reliability and serviceability.

The XA.5 Series amplifiers have a much larger output current capacity than earlier XA Series models. They can deliver more than five times the current – more than 25 times the power into very low impedance loads. This enables the XA.5 Series Amps to handle with ease what are usually considered very difficult loudspeakers.

XA.5 Series Power Amplifiers are available now from authorized Pass Labs dealers. Suggested retail prices are $34,100/pr for the XA200.5, $22,000/pr for the XA160.5, $16,500/pr for the XA100.5, $11,000/pr for the XA60.5, and $5,500 for the XA30.5.

About Pass Labs

Founded in 1991 by legendary audio designer Nelson Pass, Pass Laboratories, Inc. markets its unique amplifiers, preamplifiers and speakers throughout the world. The company has been based in Foresthill, California, since its beginning, and is widely regarded as one of the most innovative audio brands in the world. Its critically acclaimed Aleph, X and XA-Series products have won numerous awards, and Founder Nelson Pass holds numerous audio patents. His achievements include developing the first dynamically biased Class A amplifier circuit in 1974, developing a fully cascode audio power amplifier in 1976, and developing the Stasis amplifier in 1977. He helped popularize solid-state, Class A power amplifiers, and developed the very successful Aleph series of products, and the Super-Symmetry™ circuit, which achieves exceptionally low distortion 4 and noise levels. The company is now poised to introduce a new generation of amplifiers and other high-performance audio products.