Review: Pass Labs XA-100 monoblocks Amplifier

Category: Amplifiers

I first would like to share a very brief history of what amps I have used before, in a bi-amped configuration, that came before the Pass Labs XA-100 monoblocks, to bring a perspective of why I believe these monoblocks are the best amps I have ever had in my system.

I have always bi-amped my MG-20's, which have been in my system for over 14 years. I still use a pair of Threshold SA-1's to power the bass panels. I used a pair of Pass Labs Aleph 1's for close to 9 years to power the midrange and ribbon tweeters of the 20's. I loved the warmth/musicality/richness of the Aleph's in my system, but became curious about some of new SS designs that were being highly regarded. At the same time Pass Labs had come out with their new X series amps, which I found to be much more dynamic/detailed/transparent then my Alephs, but were somewhat "cool" for my sonic taste and not as musical as the Aleph 1's. Finally, I auditioned an Edge NL-10, that was a terrific amp in that it had all the virtues of SS design, dynamics/details/extension, and still offered a very "musical/silky" sonic signature. So, I made the change and was very satisfied for over two years.

Then Mr. Nelson Pass and his team At Pass Labs came out with his XA series and X-.5 series. When I auditioned the 350.5 it knocked my "sonic socks" off because it had all the virtues of the Edge NL-10, dynamics/transparency/extension to a somewhat better degree, but added more realistic timbres, more air around players in a larger soundstage and finally what I just like to refer to as "musicality/liquidity" that just sounds more like real music to me. The 350.5 offered a few watts of single-ended class A before going into the next 50 watts of class A before finally going A/B biasing. So what would the XA amp's offer sonically, that only offer and stay in single-ended class A mode?

All the Pass Labs amps are beautifully built and are real gems visually, including the XA-100 monoblocks. I never in any of my reviews spend time on design or mechanics because its easy to go the website to get those details, I rather just share the sonics of the piece I have auditioned or have decided to put in my system. I believe informed audiophiles know that Nelson Pass is a genuis and his products have the highest build quality and engineering in high end audio.

I could give you paragraphs of audiophile cliches regarding the beauty of XA-100's, but I'll spare you and be succient regarding the details of their sonics. Everything that the 350.5, which still is a wonderful amp, had to offer was improved in what I call the "analytical" categories that audiophiles use to dissect the sound of amps. Yes, the Xa-100's were great in those areas, such as details, total and complete transparency, the most realistic and natural timbres I have ever heard, a top end that is airy and natural, midrange bloom but without losing mico-dynamics and decays, rock solid imaging on a realistic sized sound stage with most air and a three-dimensionality to the players that I have ever heard in my system. Good stuff.

But, what really amazed and delighted me was the "pure", I know this a very subjective, "musicality/effortlessness" of these monoblocks. Not "layed back" or a "fat tube sound", but just a true beauty that allows you just to relax and enjoy the music and not be aware of any specific aspect of the overall listening experience. Now, don't get me wrong, the dynamics,prat,drive of the music is there, but is offered in an overall perspective which just seems more natural compared to any other amp I have ever auditioned in my home system. Peter, one of the good guys at Pass Labs, had a great way to describe this quality," the XA amps just invite you into the music, more then other amps", its a great way to put the experience into words.

Please, I'm not saying these are the GREATEST amps in the world, their is no GREATEST, but the XA-100's I believe rank right up their with the other world class reference amps available today. If what I wrote has conveyed to any great degree what the XA-100's have to offer, I hope you might now be curious to hear them yourself and come to your own conclusions regarding their sonic virtues. These monoblocks are going to stay put in my home rig and I feel lucky that I could muster up the cash to keep them.

A final note. Through the years I have found the people at Pass Labs, including Nelson Pass, to be generous with their time on the phone, always willing to answer any qusetions, and I believe to be very honest regarding their products. Both Peter and Kent are fine gentleman, this time I spent more time harassing Peter regarding all kinds of matters regarding the XA amps, and he always answered my questions in a very informative and friendly way. Thanks Peter.

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Teajay, could you tell us more about the audible differences between your former X350.5 and your new XA100 monos? What are the strongest features of each
unit? What difference between the two caused you to make the final swap decision? Did you find the stage to be at all smaller on XA100 than on 350.5?
What about authority?

I am pleasantly surprised that the XA100 monos will drive your notoriously power hungry Maggies 20s with ease. . . Kent last year had warned me that the
XA series may not have had sufficient current to drive difficult load such as what's found in the maggies. I am delighted to hear that he was in fact
just erring on the side of caution.
Guidocorona, I too was concerned regarding if the XA amps would have enough current/drive to adequately power my MG-20's, that's why I first went with the 350.5 with great results. Remember, I bi-amp so the 350.5 was only driving the midrange panels and ribbon tweeters, not the bass panels. However, regardless of the type of music or volume levels that I normal listen to, the 350.5 never really moved out of its 50 watts of class A and maybe crossed over into A/B for a very few watts on the largest transient peaks. So, this lead to many discussions regarding the nominal ohm rating of Maggies, which is six, that they are not necessarly a hard load, but love current and finally their not the most efficient speakers as you stated in your post. Well, and I'm thrilled about this, I hear absolutly no strain, compression or distortion on any type of music or volume levels in my system.

To address your three main questions regarding the sonic differences between the XA-100's and the X-350.5 which lead me to make the change:

1) The soundstage is not smaller or bigger with the XA-100's compared to the 350.5, but I believe more accurately gives you what the recording has to offer. Also, since the XA-100's have the greatest image density and air around individual players with a three dimensionality I have ever heard in my system, the amps give you a sense of "intimacy" that kinda brings you closer to the source without shrinking the soundstage. If your listening to a big band recorded in a large acoustic space you get it, if if its a quartet in a small club that's what you hear. Now, remember, up to hearing the XA-100's in my system the 350.5 produced the best soundstage I had ever heard, compared to my Edge NL-10 a fine amp that came no were close to the 350.5's soundstage both in height or width and layering in the acoustic space, but the XA-100's are qualitatively better in my opinion.

2) I do not like to write descriptions of the sonics of different gear in highly subjective or mumbo-jumbo ways, however, sometimes its hard to describe special qualities only in analytical/objective semantics. In this case, its regarding your question conerning the authority of the XA-100's. Well, how about this fractured analogy, the XA-100's are the proverbial " iron fist in a silk glove". They offer great dynamics with terrific weight to the different players, yet at the same time are easy, relaxed, and airy at the same time. Hope that makes some sense to you.

3) The reason I decided to make the switch from the 350.5 to the XA-100's, and feel very fortunate that I can, mainly comes from a very special aspect that you get with the XA-100's, which the 350.5 offered a small taste of, which is these sense of "easyness/effortlessness/liquidity" that just lets me in a more natural way get more into the music. I'm not talking about an euphonic coloration or a fat over ripe richness I have heard with certain tube amps, but a wonderful ease and natural presentation that makes it easer to relax and enjoy the music I'm listening to. That does not mean that these amps lack impact or prat, I was just listening to Charlie Hunter's, Steady Groovin', and the music was rocking my room, but that special quality of drawing you in to the music was still making it easer to get into, in this case, the groove.

I enjoyed totally my time with the 350.5 powering my system for over a year and a half. I still think it's one of the best SS amps out on the market and will compete with virtually anything in a highly competitive way. The XA- amps will not power as well some very difficult speaker loads, were the 350.5 well sound and work better, but if XA-amps can control the speaker, I believe they offer something very few amps have in their sonic signture. Remember, at this level of gear , their are many great sounding pieces, so personnal taste and synergy are really the final determinant. For me the XA-100's are the best I have heard in my system. Please, Guidocorona, if I'm still not answering your questions specifically enough let me know and I'll try my best to address them in a more helpful way.

I agree with you on the opinions of XA-100 but I drive a much easy load, Dunlavy SC-4. Just wonder have you ever tried driving maggie witn XA-100 only, no bi-amp ? The sensitivity is about 6dB difference. Thanks!
Well Cdma, if you have the XA-100's already, I'm sure your system offers beautiful music to listen to on a daily basis!

I have always driven my MG-20's bi-amped and never purchased the passive crossover but always used a Bryston active crossover. The passive crossover from Magnapan is no longer available. In the past my experience has been that MG-20's have always sounded better when bi-amped then being driven by one amp through their own passive crossover. Besides, I'm using another Nelson Pass gem on my bass panels, a pair of Threshold SA-1's that I still great amps in their own right.
Just wanted to share that I now have close to 200 hours running time on the XA-100's and the amps' sonic virtues are becoming more apparent as they break-in.

Even more of a commanding presence with rock solid images and great air around individual players, and yet they sound even smoother with greater liquidity then they did earlier on. Well, can they even improve more? I don't know, but boy, they sound pretty terrific right now.