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Pass Labs Introduces XA.5 Series Power Amplifiers, Designed for and by Audiophiles  Print E-mail
Home Theater News Power Amplifier News
Written by AVRev.com   
Thursday, 20 December 2007

Pass Laboratories, Inc. introduces the XA.5 Series Power Amplifiers at the 2008 International Consumer Electronics Show, next month in Las Vegas. Designed for audiophiles by lifelong audiophiles, the new amplifiers represent a peak in the evolution of Pass Labs amplifiers toward ever higher performance.

The XA.5 Series consists of five models — the XA200.5, the XA160.5, the XA100.5, the XA60.5 and the XA30.5 Power Amplifiers. All embody significant improvements on their classic Pass Labs predecessors, and all deliver the warmth, sweetness, depth and space that are the hallmarks of outstanding audio products.

In design terms, the new amplifiers’ hallmarks are power and control. No matter what the loudspeaker, XA.5 Series Amplifiers have the power and stability essential for music without strain. They possess the dynamic range to do justice to the 24-bit recordings of the Twenty-first Century, and the elegance to retrieve the micro-dynamics the most sensitive loudspeakers offer. They also have the ability and power to move easily from total silence to explosive transients without losing information.

XA30.5 Power Amplifier

Most significant, the XA.5 Series amplifiers have tremendously larger output current capacity than corresponding models from Pass Labs’ earlier XA Series — more than five times the current, which is more than 25 times the power into very low impedance loads. This makes XA.5 amps entirely appropriate even for loudspeakers with very difficult loads.

The XA.5 amplifiers achieve their superb performance by incorporating all the refinements Pass Labs quietly introduced into its earlier models over the past several years, as well as through pure Class A operation. The refinements include lower distortion at all power levels and into all types of loads, especially the all-important audio midrange; and greater control over the large heavily biased follower output stages, which have low output impedance for consistently high damping under all load and signal conditions. Additional refinements include:

Greater stability. XA.5 circuits do not compensate for any type of high frequency by using little frequency roll-offs, lag capacitors, output coils, Zobel networks, or other techniques. The amplifiers are stable because they are simple gain stages with minimal feedback.

Lower noise. About one-tenth the noise from the audio to the radio frequency spectrum. The circuits are immune to environmental noise, and more immune than most to mechanical transformer noise from bad AC lines.

Better bias control. The amplifiers’ idling current is dramatically more constant against variations in temperature, line voltages, and signal transients. They also require less warm-up time to reach optimal performance.

Higher efficiency and more power. The circuits operate 20 percent more efficiently, leading them to deliver approximately 20 percent more output power.

Greater reliability. XA.5 amplifiers are harder to break, and easier to repair if they do.

Pass Labs achieved these performance refinements by gradually implementing in its amplifiers several significant improvements, more than space permits fully describing. For example, Pass Labs replaced input differential MOSFETs with JFETs possessing much less noise, higher in°©put impedance, and greater linearity. They added more power output devices to improve power handling and linearity. They developed a new bias generator that eliminated three sources of variation in the output stage bias current. They improved the power supplies by adding storage capacitance, larger and quieter power transformers, and fast-recovery rectifiers. They improved the wiring and circuit board layout in ways that lowered noise and distortion, and improved reliability and serviceability.

Super-Symmetry and the Birth of X
Of course, all the XA.5 amplifiers also employ the acclaimed Super-Symmetry or “X” circuit developed by Nelson Pass, which improves performance by canceling distortion and noise. To the extent that distortion and noise can be made to appear identical by precisely matching characteristics of the two halves of a balanced amplifier, they will not be detected.

Pass Labs introduced Super-Symmetry in the X1000, the first of its X Series amplifiers, in 1998. In 2002, Pass Labs combined Super-Symmetry with the Aleph single-ended Class A output circuit Super-Symmetry had initially supplanted, in the XA series of amplifiers. Pass Labs discovered the two circuits complemented each other so well they might have been developed together.

More improvements followed. By 2003, the accumulating enhancements warranted changing the des°©ignation of further new amplifiers to X.5. The new XA.5 Series amplifiers incorporate all the improvements and refinements Pass Labs has introduced over the years for its finest achievements yet in the art of amplification.

The New Models

The XA200.5 Amplifier drives 200 watts per channel at 8 ohms with a gain of 26db and 1 percent THD. Its input impedance is 30 Kohms balanced, 15 Kohms unbalanced; and its power consumption is approximately 700 watts, idle. It measures 19 x 11 x 28 inches (W/H/D), and weighs 180 Lbs.

The XA160.5 Amplifier drives 160 wpc at 8 ohms with a gain of 26db and 1 percent THD. Its input impedance is 30 Kohms balanced, 15 Kohms unbalanced; and its power consumption is approximately 600 watts, idle. It measures 19 x 11 x 21.5 inches (W/H/D), and weighs 150 Lbs.

The XA100.5 Amplifier drives 100 wpc at 8 ohms with a gain of 26db and 1 percent THD. Its input impedance is 30 Kohms balanced, 15 Kohms unbalanced; and its power consumption is approximately 300 watts, idle. It measures 19 x 7 x 19 inches (W/H/D), and weighs 110 Lbs.

The XA60.5 Amplifier drives 60 wpc at 8 ohms with a gain of 26db and 1percent THD. Its input impedance is 30 Kohms balanced, 15 Kohms unbalanced; and its power consumption is approximately 200 watts, idle. It measures 19 x 7 x 19 inches (W/H/D), and weighs 75 Lbs.

The XA30.5 Amplifier drives 30 wpc at 8 ohms with a gain of 26db and 1 percent THD. Its input impedance is 30 Kohms balanced, 15 Kohms unbalanced; and its power consumption is approximately 200 watts, idle. It measures 19 x 7 x 19 inches (W/H/D), and weighs 75 Lbs.

All five XA.5 Power Amplifiers are available now from authorized Pass Labs dealers at the following suggested prices:

Amplifiers MSRP
XA200.5 $31,000/pair
XA160.5 $20,000/pair
XA100.5 $15,000/pair
XA60.5 $10,000/pair
XA30.5 $5,000 each







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