Wednesday, November 30, 2016

Pass Labs XA25

































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 in Auburn, California.

They measure well, sound great, and are reliable. Twenty years of ongoing innovation have kept the X and XA amplifi ers at the forefront of high-end audio. The XA25 embodies all this and less. A smaller stereo Class A 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 means 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 uses two pairs of NOS complementary Fets in common-source mode in a current feedback (CFA) confi guration. The amplifier is direct coupled and has no DC servos or frequency compensation. 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.


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 ohm, 1 KHz, 0.1% @ 50 Watts, 4 ohms, 1 KHz

Freq. Response: DC to -3 dB @ 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

Idle Power draw: 200 Watts total.

Dimensions: 17”W x 17.375”D x 6”H

Weight: approx. 55 lbs

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