- Written by Chris Groppi
- Published on 06 July 2009
- Pass Labs XA30.5 Stereo Power Amplifier
- Page 2: Design of the Pass Labs XA30.5 Stereo Power Amplifier
- Page 3: The Sound of the Pass Labs XA30.5 Stereo Power Amplifier
- Page 4: The Pass Labs XA30.5 Stereo Power Amplifier On the Bench
- Page 5: Conclusions About the Pass Labs XA30.5 Stereo Power Amplifier
- All Pages
The XA30.5 is the finest amplifier I have had in my listening room. This was actually quite surprising to me. While I expected the amp to be fabulous, I thought the low power output would handicap it when deployed in my room with my speakers. The Gallo Reference 3.1s have 88 dB/W/m sensitivity. While this is not low sensitivity, it's not particularly high either. From the first instant I listened to the XA30.5, it was clear this assumption was incorrect. In retrospect, this should not have been a surprise. Most music (even at pretty high volume) happens at well under 30W. Only bass transient peaks when listening at high volume caused the current meter on the Pass amp to move at all. When the needle did move, it only moved by a small amount. This says that the Pass amp was almost always operating in class A, tipping into class AB only occasionally.
The Pass amp has stupendous current delivery capability, with its huge transformer and loafing output devices. Large-scale dynamics, when compared to the 500W Emotiva XPA-1 monoblocks, were only very slightly diminished and then only on hardcore, bass heavy electronica and rock. This was the only place where the XA30.5 wasn't clearly superior to the XPA-1s (which are admittedly less than half the price of the XA30.5). On bass heavy electronica like Daft Punk's Human After All and Crystal Method's Vegas, the extension, control and power was there, but the sharp leading edges of transients produced by the more powerful amplifiers were rounded off a bit. In terms of microdynamics, the XA30.5 was superior. The aliveness of the XA30.5 was unmatched in my experience. The XA30.5 retained the energy and pace of the Emotivas on every album I listened to, but did so with superior smoothness and imaging.
The reality delivered by the Pass amp was its greatest asset. This was due to a combination of the great microdynamics delivering that "alive" sound, combined with stupendously three dimensional and well-defined images. Each image in the soundstage was amazingly round and deep when compared to the typically flat delivery from most amps. Overall soundstage width, and particularly depth, was also the best I've heard from the Gallos in my room. Width was about 1 foot wider on each side than the XPA-1s. The depth, which is mainly a result of spatial acoustic cues being clearly extracted from recordings, was absolutely insane. With recordings that had the information in them, like several of my Acoustic Sounds purist blues recordings, the depth was such that some of the soundstage sounded to be so far behind the speakers that it was in my front yard. On highly engineered recordings, the flatness was still there. An amp can't put in information that has already been engineered out. Even with these flat recordings (which are most of them), the three-dimensional nature of the images was still there, they were just all arranged in a single plane. An example of this was Gomez's Bring it On, with beautifully round images, but all in one plane just behind the speakers.
One thing class A amplifiers are known for is an incredibly liquid, clear and smooth midrange. The XA30.5 did not fail to deliver. The absolute clarity of the midrange combined with a complete absence of grain, glare or hardness was addictive. Unlike some tube class A amps, there was no trace of added warmness, just complete clarity and transparency, but delivered with a smooth-as-silk lack of grain. My favorite examples were the simple vocals of Allison Krauss and Ralph Stanley on the SACD recording of the O Brother Where Art Thou soundtrack. With the XA30.5, these simple unaccompanied vocals were just stunning. Some class A amps also have limited high frequency extension, but not this amp. I think some of these preconceptions are the result of single ended class A vacuum tube amps, which have some major technical limitations.
The solid state XA30.5 has no such limitations, with high frequency extension flat to well past 50 kHz. The high end also has stupendous smoothness and liquidity, giving every recording a much-improved sense of smoothness and "ease," meaning a lack of grain and glare at the high end. This is the stuff that can give you a headache after listening for a long time, or feels like a "pressure" on your ears. You'll only know it was there when you can take it away. The XPA-1s could not match this smoothness and ease. This was another area of the XA30.5 performance that benefited every recording. While they had the extension, accuracy and precision, the low order distortion spectrum of the XA30.5 gave it a major edge in the reproduction of the midrange and treble.
In the bass, the XA30.5 delivered admirably well-controlled and tonally accurate bass, but lacked a bit of the sharp edged impact of the more than 15 times more powerful XPA-1. This rounding off of the dynamic impact in the bass was the only limitation of the XA30.5, and this was compared to an amp that excels in this area. With even a slightly more sensitive speaker (I would say anything over 90 dB/W/m), the XA30.5 would catch up. For less sensitive speakers, there are plenty of XA amps with higher powers, from 60W to 200W class A power. These are all monoblocks, and much more expensive than the XA30.5, though (starting at over $11k).