Pass Lab X1 pre-amp and XA100 monoblocks

Source: Haute Fidelite June 2005

Audio veteran Nelson Pass has been titled Mr. Class-A as he has designed behemoths Class-A amplifiers under numerous brands for years. It's under Pass Labs, however, where he has been able to summate and implement his overall design philosophy.

Haute Fidelite tested X1 pre-amp with XA100 monoblocks. Like many high-end pre-amps, the X1 is a two chassis construction, and has three features I consider essential for a pre-amp: state-of-the-art volume control, variable gain settings and full balanced circuit. The volume control is an intriguing implementation as it's essentially a fixed resistor attenuator under digital control. With regard to the XA monoblocks, the very first thing everybody notices is their most dramatic-looking exterior design (see pic. below).



Compared with Pass Labs' X-series, the more upmarket XA-series "accentuate performance over power", according to manufacturer's Web site. As with all Pass Labs amps, XA-series employs low global feedback and "Supersymmetry" circuit, which according to company, reduce overall distortion by as much as 99%.

Back to review. Laurent Thorin observed:"...low end was tuneful, incredulous energic and precise ... mids were astonishingly rich and fluid ... voices were unsettlingly real ... highs materialized with subtlety and delicacy ...". Moreover, he noted that in subjective terms the XA100s sounded 2 or 3 times more powerful than their actual 100 watts. Thorin bestowed "Haute Fidelite Reference" designation for the combination.

Although Pass Labs product reviews are quite rare, all I've seen characterized the sound in pretty similar fashion. The extreme dynamic range and definitive bass control, warm midrange and sweet top end, and a subtle, velvety character that floates images in superbly three-dimesional soundstage. Anthony H. Cordesman in the Absolute Sound August/September 2004 issue said about XA160 monoblocks: "It is the most tube-like transistor amplifier I have heard in the positive sense of "tube-like". This is an amplifier with soul." And while reviews highlight the realistic warmth and lifelike nature of XA-series, equally reviewers have noticed that XA amps don't possess the ultimate resolution.

The XA160 review in Stereophile by Michael Fremer was curious as evidently the early production run of the amplifier suffered from an internal wiring error, resulting in distorted sound and low maximum power. The measurements also illustrated quite low input impedance, at 19.5k ohms balanced and 12.7k ohms unbalanced.

If you are interested, there is a fascinating review of XA160s by Dr. Poltum, the Director of Archives for the prestigious Vienna State Opera/Philharmonic Orchestra. Look at their reference system: Pass Lab's amplification, Wilson Puppy 7 speakers, SME 30/2 turntable w/ SME V arm and top cartridges like Koetsu Platinum Jade, Accuphase DP-85 SACD/CD-player and Mark Levinson Reference CD transport, and Transparent Reference XL cabling. Worthwhile article to read, especially how musicians themselves decribe the reproduction of sound of their own recordings.

Viewpoint: The diversity of high-end amplifiers is staggering. On the one hand there are occasional hobbyist-professionals handcrafting esoteric amps and on the other there are potent manufacturers with staying power like Accuphase or Mark Levinson that produce extremely high-quality, great sounding amps aiming to the most neutral reproduction of sound.

Personally I find the most compelling the high-end amplifier manufacturers like Ayre, Audio Research, Burmester, Edge, Halcro, LAMM, Pass Labs, and to some extent, Krell. Why? Because the amps from these companies tend to embody one bold thinker's vision, imagination and creativity what an amplifier should be and do. Although aforementioned companies produce sometimes utterly different designs than the others' ones, their amplifiers are designed with an attitude and personality and exhibit a difference in their designers' points of view. Some excel in resolution (like Halcro), some leave the reviewers searching words to describe the "rightness" of the sound they are experiencing (like with LAMM), and some take price-point-no-issue approach (like Burmester). But at least they express something distinctive, some even have soul.