Pass Labs XP-22 Preamplifier and XP-27 Phonostage

I’ve had Pass Labs power amplifiers in my audio system for more than 20 years. A pair of Aleph 0 monoblocks was first, eventually joined by an X5, when I took the plunge into multichannel music. Now, I employ three XA 60.8s for the main-front and center channels, plus an Aleph 0s for the surrounds. For some reason, in all that time, I never tried a Pass preamplifier. So when Robert Harley proposed a review of the Pass Labs XP-22 preamp and the XP-27 phonostage, I leaped at the chance. Ok, that’s not entirely true—I didn’t leap. My leaping days are over. But I did stand up very quickly when I got the news. I have witnesses.

Even steadfast admirers of Pass electronics may not be aware that the company’s products have long been designed by two individuals, founder Nelson Pass and Wayne Colburn. Colburn first worked with Pass at Threshold Audio in the 1980s, and later joined Nelson at his new company, soon becoming a partner. There’s definitely a division of labor at Pass Labs, with Colburn largely responsible for the preamplifiers, integrated amps, and the manufacturer’s only DAC to date, while Pass himself is in charge of the “big iron”—i.e. the power amps. However, the two are in constant dialog when developing new models, and, as expected, listen critically to each other’s designs. Even for these hardcore engineering types, listening outranks measurements in the evaluation process.

Pass Labs launches new models relatively infrequently—a product life of seven or eight years is typical. When I asked Wayne Colburn what prompted the introduction of the XP-22 and XP-27, he responded that “some of this was regulation driven for emissions and safety standards. This led to power supply redesign with new lower-noise transformers and EMI control. We also upgraded our Audio Precision [analyzer] to the latest model and upgraded our ability to correlate measurements with sound.” 

Highly regarded for the volume controls he designs, the famously self-effacing Colburn does his best to give the credit to the semiconductors utilized: “Just a state-of-the-art chunk of silicon,” he said. “I have worked on volume controls since the Forte 44 and Threshold T2, and they are pretty critical. (Forte was a lower-priced Threshold product line.) I had my own unique design in the original X preamps, and then NJR from Japan paid us a visit with a new part. They seemed rather proud of it, and Nelson and I gave it a try. I was skeptical but pleasantly surprised. They had done a great job—a compact solution with no inductance or capacitance due to packaging or layout, and great matching, coupled with transparency.”

The power supplies are dual-mono, employing very quiet, double-shielded toroids that have lowered the noise floor over prior models. The output stage is more robust, which makes driving long cable runs easier. In all their products, Pass and Colburn strive for simple circuits and use parts with the most linear behavior. As low-level nonlinearities are additive in their impact on sound quality, avoiding them in the first place reduces the need for negative feedback—a technique that itself has a deleterious effect on sonic neutrality and detail.

The XP-22 preamplifier is a two-chassis design, the control module attaching to the identically sized power supply with a 9-pin JAE umbilical cable. The two boxes are stackable, and there are pieces of felt glued to the bottom of the preamp’s four feet to prevent scratching the top surface of the power supply. The owner’s manual does comment that the “best performance” results when the power supply is sited on another shelf. The rear plate of the power supply sports an IEC 320 power receptacle with an associated rocker on/off switch, as well as the connection for the JAE cable. A discrete blue LED on the front panel of the power supply lights up when the preamp is turned on.

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