Pass Labs INT-25

Description

At Pass Labs we build FET amplifiers with oversized output stages, massive heat sinks and huge 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. Over twenty years of continuous innovation have kept the X and XA amplifiers at the forefront of high-end audio.

The INT-25 embodies all of this and less. A smaller stereo Class A amplifier at a lower price, it takes advantage of lower power requirements to feature a simpler single-ended circuit and fewer parts in the signal path. This also allows the elimination of degeneration, “that other negative feedback” across all stages.

Simpler designs with fewer gain stages improve speed and stability. Lower voltages mean that gain devices can be operated at higher bias currents, deeper into Class A. The latest Power FET technology replaces banks of small parallel transistors with a single pair of industrial-grade devices, each rated at 700 watts / 40 amps. With no current-siphoning issues and a new constant-current bias circuit to compensate for temperature variation, they are connected directly to the loudspeaker without ballast resistors to achieve the lowest possible distortion and the highest damping factor. The absence of degeneration also increases efficiency and Class A operating current, allowing for extended Class A operation with reactive and low-impedance loads.

The simple front-end circuit uses two pairs of our favourite NOS complementary FETs in common-source mode in a current feedback (CFA) configuration.

The preamplifier section is a simplified single-ended version of the one used in the INT-60 and INT-250, featuring three line-level inputs and no line-level output.

Everything done in the signal chain from the microphone to the loudspeaker leaves an indelible mark on the music forever. The XA25 amplifier section is direct-coupled and requires no DC servos or frequency compensation, neither adding to nor subtracting from the experience.

As with all Pass amplifiers, the technology and construction are strictly in the service of the listening experience. The INT-25 measures superbly, but its subjective qualities are very special. In an industry where products with excellent specifications are often found to be dry and boring, this amplifier breathes new life into music.

Specifications:

• Class: A
• Type: Stereo
• Gain (dB): 29/35
• Volume control (1dB steps): 63dB
• Remote: yes
• Entries: 3
• Departures: 0
• Power output / channel (8 ohms): 25 watts
• Power consumption (W): 200
• Standby power consumption (W): <1
• Dimensions (W x H x D): 43.18 x 44.13 x 15.24
• Weight: 22 kg