Pass Labs

INT-25

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 plus years of ongoing innovation have kept the X and XA amplifiers at the forefront of high-end audio.

The INT-25 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 two pairs of our favorite NOS complementary Fets in common-source mode in a current feedback (CFA) configuration. 

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

Everything done in the signal chain from the microphone to the loudspeaker, forever leaves an indelible mark on the music. The XA25 amplifier section is direct coupled requiring no DC servos or frequency compensation, neither adding too 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 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.

Features

• Power Output: 25 Watts per channel into 8 ohms (50W into 4 ohms). 
• Class A Operation: The INT-25 is a Class A amplifier, meaning it operates with a constant current at all times, even when not playing music. This results in a smoother, more natural sound.
• Simple Design: The INT-25 is a line-only amplifier, meaning it has no features like digital inputs, network connectivity, or a phono stage. 
• Inputs: Three line-level RCA inputs. 
• Volume Control: A 63-step volume dial for precise adjustment.
• Output: Five-way gold speaker cable binding posts. 
• Chassis: A large chassis with two side-mounted heatsinks for efficient heat dissipation. 

Specifications:

• Inputs: Three (3) RCA
• Gain: 26dB
• Output power: 25 Watts rms @ 8 ohms 50 Watts rms @ 4 ohms
• Distortion: 0.1% @ 25 Watts, 8 ohms, 1 KHz
• Frequency response: DC to -2 dB @ 100 KHz
• Residual Noise: < 150 uV output, unweighted 20 to 20 KHz
• Damping Factor: 500
• Input Impedance: 48 Kohm
• Idle Power draw: ~2.25 Amps @ 120 VAC
• Dimensions: 17”w x 17.13”d x 6”h
• Weight: 51 lbs