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Pass Labs New More Affordable XA Series Class A Power Amplifier

"The XA2 is an affordable transition amplifier enabling the discriminating Music Lover to move to Class A Technology."
- Nelson Pass

Pass Labs XA Power Amplifier

Pass Labs has started shipping their new XA25 Class A Power Amplifier, the most affordable power amplifier in their current line. With 2 x 25W @ 8 ohms, 2 x 50/W at 4 ohms and 2 x 100WClass A/AB at 2 ohms, and priced at $4900, the XA25 is not meant as merely an "Entry-Level" model, but rather, a more affordable way for consumers to experience the Pass Labs line and all its renowned traditions of founder Nelson Pass’ comprehensive design, construction and performance.

In other words: A smaller, lighter and less expensive Pass Labs Class A power amplifier.

To paraphrase the words of Nelson Pass when describing the new XA25 Power Amplifier: At Pass Labs, we build FET amplifiers with excessive output stages, huge heat sinks and massive power supplies. We use the highest quality components in simple linear topologies, assembled and tested with care and subtlety. They measure well, sound great, and are reliable. Twenty+ years of ongoing innovation have kept the X and XA amplifiers at the forefront of high-end audio.

"The new XA25 is intended to appeal to those wanting the performance without the frills in a chassis that will fit on a shelf and can be lifted without the assistance of ruffians." - Nelson Pass

The XA25 embodies all this and less. A smaller Class A stereo amplifier at a lower price, it takes advantage of the lower power requirements to have simpler single-ended circuitry and fewer parts in the signal path. This also allows elimination of degeneration, "that other negative feedback," in all stages.

Simpler and fewer gain stages improves speed and stability. Lower voltages mean the ability to run gain devices at higher bias currents, more deeply into Class A.

Newer power FET technology replaces banks of parallel small transistors with a single pair of industrial devices, each having a 700 watt / 40 amp rating. With no current-hogging issues and a new constant-current bias circuit to compensate for temperature drift, they connect directly to the loudspeaker without ballast resistors for lowest possible distortion and highest damping factor. No degeneration also increases the efficiency and Class A operating current, allowing greater Class A operation into low impedance and reactive loads.

The simple front end circuit uses two pairs of NOS complementary FETs in common-source mode in a current feedback (CFA) configuration. The amplifier is direct coupled and has no DC servos or frequency compensation. Inputs from the preamplifier or DAC are RCA.

According to Nelson Pass: "As with all Pass amplifiers, the technology and construction are strictly in the service of the listening experience. The XA25 measures superbly, but its subjective qualities are most special. In an industry where products with great specs are often found to be dry and boring, this amplifier breathes new life into the music. "It follows the philosophy of PL amplifier design – still greater performance with still simpler circuitry."

Specifications

  • Output power: 2x 25 Watts Class A @ 8 ohms, 2x 50 Watts Class A @ 4 ohms, 2x 100 Watts Class A/AB @ 2 ohms
  • Distortion: 0.1% @ 25 Watts, 8 ohms, 1 KHz, 0.1% @ 50 Watts, 4 ohms, 1 KHz
  • Freq. Response: DC to 3dB @ 200 KHz
  • Gain: 20 dB gain
  • Noise: Output 100 uV unweighted 20 to 20 KHz
  • Damping Factor: 200
  • Slew: 100 V/uS
  • Input Impedance: 47 Kohm
  • Peak Current: 10 Amp output (200 Watts into 2 ohms) Independent of loudspeaker load phase.
  • Protection: Shutdown at 10 amps output
  • Idle Power draw: 200 Watts total
  • Dimensions: 17" W x 17.4" D x 6" H
  • Weight: 46 pounds/21 kilograms
  • Price: $4,900 MSRP

About Pass Labs

Founded in 1991 by legendary audio designer Nelson Pass, Pass Laboratories, Inc. markets its unique amplifiers and preamplifiers. The company is based in Auburn, California, and is universally 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, developing a fully cascode audio power amplifier, and developing the Stasis amplifier in 1977. He helped popularize solid-state, single-ended Class-A power amplifiers, and developed the very successful Aleph series of products, and the Super-Symmetry™ circuit, which achieves exceptionally low distortion and noise levels.

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