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.
My major audiophile friend and buddy who has great ear's, always tells the truth, and is very experienced with Pass Labs gear just spent 4 hours listening to the XA-100's in my system.

He loves the 350.5 amp and thought before he sat down to listen to the XA-100's that they would not be that much better then the single chassis 350.5.

Well, to use his words, " these amps take everything to another level of refinement". He found them to be another step towards musicality and "ease" that is so pleasurable to experience when you hear it. He still thinks the 350.5 is a great amp, but now believes the XA amps offer even more "special stuff" then the .5 series amps.
Teajay, thanks for the review. I currently use the X250.5. Hopefully when finances allow, I'll follow your path to the XA's! The 250.5 was mind-bogglingly good compared to my previous amps. Nelson Pass is a genius indeed.
I agree with your perspectives on the X350.5. I've had one for a year or so and agree that it's very good. However, it lacks that certain something that I had with my Aleph 5, which was supplanted by an X350 due to its lack of power. The 350.5 is a very significant improvement over the X350 throughout the spectrum and in listening ease, but it lacks the naturalness that the single-ended Alephs provided. I'm now considering an XA100 for just that reason.

One thing that I can't answer and one that gives me some pause is the XA100's performance on bass. The 350.5 is great in the bass department (although I wish it didn't have such a high damping factor). Biamping, using a 350.5 to drive just the mids and treble seems a huge overkill, but that's your business. I have speakers that are 90 db efficient into 8 ohms and dip no lower than about 7.

Since you don't use your XA100s in that regard, I suppose you can't tell me about their performance driving full-range speakers, but do you know anyone who has used them in that regard?
Islandbird, I wish I could refer you to someone I know who uses the XA-100's to drive their speaker full range, but I don't know anyone who uses them that way.

My strong hunch is that if your speakers do not go below six ohms and are 90 db efficient the XA-100's would have no problems powering your system. Also, you would be enthralled with their overall sonic signature, in that they have the magic of the older Aleph design with the dynamics/clarity/extension of the X series, and the bass is both gutsy with accurate timbres.
Thanks for the perspectives. I was also considering the XA160 for the extra wattage, but reasoned they are just too large and crank out too much heat to justify those 60 extra watts. Another sixty isn't all that much anyway once you have that first 100 in place.

I know I'll love the sound of the XA100, but I'm trying to get a handle on what I might miss (if anything) that the 350.5 provided before it slips away. Sort of trying to second guess myself in advance for a change.

I'd considered an Aleph 2 before I bought the X350.5 but reasoned that most available units had already had too much current over the dam. The only pristine pair I saw advertized was snapped up in a hurry. The XA100 was the logical alternative....wish I'd followed my instincts. Once one gets used to that SE sound, it's tough to settle for anything else.
Sorry to digress just a bit....

but could anyone please suggest - for the first time Pass owner - which Pass Labs model might offer the best point on the value curve? With sufficient power for Maggies?

Teajay, nice review.
, it all depends on what Maggies.
Cwlondon, I politely disagree with Guidocorona, the sweet spot in Pass Lab .5 series is the 350.5 when it comes to a performance/cost ratio.

The 350.5 will easily drive a MG 1.6, 3.6, 20.1 or your older Maggies to a wonderful level of performance.
No problem there Teajay, I just thought that the smaller MG 1.6 could be also driven with aplumb by x150.5 or x250.5, while the MG 20.1 may benefit from the even higher currrent afforded by the X600.5 monos. Yet these are all guesses on my part.

Yes, the "sweet spot" on the performance to cost curve (used) is exactly what I was wondering about.

Guidocorona - I have Tympani IVa's which probably need more power than 1.6's but dont know how they would compare with the 20's.

I really do love MONO blocks, however.....but will check out the 350.5...
Cwlondon, as far as I know the old Timpanis are just slightly more power demanding than the newer 20 and 20.1. I'd be very interested in reading your findings with Timpanis and the X350.5.

On reflection, I need to up the ante here...

I think these amps are so gorgeous that 2 of them is more than twice as good as just one.

So what's the best deal on monoblocks?
Cwlondon, if you wish to go with monoblocks then you are talking about either the XA-160's or the X-600.5's if you are not going to bi-amp your maggies.

In my system I am able to use XA-100's, and saved close to $5000.00, because I only use the XA monoblocks to power the midrange and ribbon tweeter in my MG-20's. However, if you are going full range with your Maggies you would have to go up to the XA-160's or the X-600.5's to power them. Both sets of monoblocks retail for $18000.00.

Take a look at the last issue of the Absolute Sound were Anthony H. Cordesman wrote a great piece on both sets of monoblocks and compared the 600.5's to the older 600's. Their is no doubt that the new .5 series is a dramatic improvement over the older X series, however the XA series are still the best in the Pass Labs lineup, with the BIG if being they have enough current/watts to drive your speakers. Remember, the XA amps are single ended class A and do not double down into lower impedence loads, that's were the .5 amps come in that will drive any speaker load.
And if budget permits, Nelson Pass has also the 200W into 8 Ohms XA200, with even more current than the XA160 monos.

Just reviewing your notes and system - wow - very nice. I am jealous.

Would you say the Thresholds and not the newer Pass Labs are the amp of choice for BASS in the maggies??

Because biamping is not out of the question.

Then of course, I can admire FOUR giant monoblocks!
Cwlondon, I would not necessary say that the Threshold SA-1's power my MG-20's bass panels better then a pair of Pass Labs X-600.5's would, but how much better would be the question.

Most Threshold and Nelson Pass fans agree that the best sounding amps that Threshold ever produced were the SA-1's. Remember, the SA-1's average 40amps and can put out 60amps, that's tons of current, which make them great bass amps with alot of control over any bass driver.

So, to replace my beloved Classic SA-1's, would cost me alot of cash, for not much of a change in overall performance. I see someone is selling a pair of SA-1's here on the Gon for around $3000.00 in mint shape, you might want to go for it, if you seriously considering biamping your Maggies.

Very tempting! So I will check them out....

Any idea how my Mark Levinson 23.5 might best fit into this scheme?

Or Threshold below and Pass above is the ULTIMATE?

Have also thought about the 600's for bass and tubes on top, but of course that is a lot more cash.

BTW, I must confess that if the Pass amps were not so beautifully designed and those blue lights didn't bring tears of audiophile joy to my eyes, I probably wouldnt bother.

But please do tell me the best way to fill my room with as many amps as possible, while bathing in blue light and old school high end sound.
Cwlondon, I don't know if their is the "BEST WAY" to fill your room with monoblocks to power your system, but if we are talking about the greatest performance for the buck, I would recommend the following.

1) A pair of XA-100's on top with a pair of the older X-600's on the bottom.

2) A pair of XA-100's on top with a pair of Threshold SA-1's on the Bottom.

3) A pair of XA-100's on top with a single chassis X-350.5 on the bottom.

4) A pair of XA-100's on the top and your ML-23.5 on the bottom.

I believe that biamping your Maggies with Pass Labs XA amps on top would bring your system to a totally higher sonic level then you have now with the 23.5 running full range.

On a totally different topic, I looked at your system, and would highly recommend that you might audition Acoustic Zen's Silver/Matrix reference II IC's and Satori speaker wire to replace your Transparent wires. I used to run reference level Transparent wires in my system and found the Acoustic Zen wires to be a wonderful match/synergy with both the Pass gear and Maggies.
I just got through reading the only professional review that I know of regarding the XA-100's, from the French journal, Haute Fidelite, written by Mr. Laurent Thorin.

Mr. Thorin, stated the following," Low end incredulous energy and precise... Mids were astonishly rich and fluid... Voices were unsettling real... Highs materialized with subtlety and delicacy". He also noted that the XA-100's, " sounded 2 or 3 times more powerful then their actual 100 watt rating". Thorin bestowed the highest honor that his journal offers, the "Haute Fidelite Reference Designation" on the XA-100's.

I guess he liked the XA-100's to say the least! It's fun for me to hear/read how other audiophiles use language to describe their experience of gear that I am already familiar with. Mr. Thorin uses a different vocabulary then I did in my review, but came to the same conclusion, the Pass Labs XA-100's are one beautiful sounding pair of monoblocks.
Many a religion is born out of deep need...few maintain a foundation for continued belief. The Devil is in the details and the practical subtelties! Krell offers as much beauty without any limitations. Also, a system is just that..a system of many components including outlets, power cords and cabling!
Astounding, I never thought of that!
According to Nelson Pass, himself, the X600.5 is the best all-around amp he has ever designed. SA-1 fans can join the Threshold SL-10 preamp fans and stasis fans, etc. but there's no getting around the fact that the current amps are better in almost all respects. Just read some of the "white papers" Pass has written concerning the evolution of his designs and class A designs in general. Some of the best aspects of his earlier designs have carried over, while he has repudiated many others as wanderings down blind alleys to make certain aspects of specific designs work, but they ultimately proved to not work as well as his simpler approaches.

From what I've managed to glean from all sources, the XA amps are the best sounding amps his primary outfits have ever produced (given the known power/compatibility caveats), and the X350.5 being the best stereo amp and the X600.5 being the best mono and therefore the best X.5 amp in the lineup. The X350.5 is the best bang for the buck in the current line-up and is all the amp most of us will ever need, and it will drive anything from Maggies to MBL's.

As for the XA amps, there are those that claim the XA160 offers the best balance of sound quality, price and power. However, within it's power band, the XA100 is the sweetest, cleanest and therefore the best sounding amp of all.
Islandbird, thanks for the info. I am still on the fence whether I should buy the 600.5 or xa160 for my BW 802d speakers. I have tried to contact Pass several time about this but still no response (something must be wrong with my email).

I've had the 802 (standard) in the house for an extended audition and they are very lively speakers. IMO the XA160 would sound the best with that speaker as the BW's could use a little softening and warmth. Power is still an issue, but I think you'd be happy with it provided you don't have a very large room (over 150 cu meters) and like to listen at 95db average and above. The 600.5 would be very good as well and would never be lacking for power with any speaker in anything short of an auditorium. I'll bet the X350.5 would also be a great match at about half the price.

I doubt if you'll get anyone at Pass to recommend an amp for those speakers as there are too many variables. Even if they were to recommend an amp they would likely err on the side of more power.

Not knowing what your tastes/room situation are, I or anyone else can only tell you what we like, it's up to you to identify what type of sound/listening you prefer and narrow your options accordingly. People claim that there's a Pass "house sound" but the X.5 and XA amps are distinctively different in what to me are some critical areas. Anyone forming opinions based upon experience with the original X series really needs to update their perspective.
I finally got a respone from Pass and they say there is no dobut about it, go for the x600.5. When I spoke with Tim from Pass on the phone there was not even a moment of hesitancy. So I guess I will be getting the 600.5!!!!
I'm not surprised, they will always recommend a healthy surplus of power. If I recall correctly, the claimed specs for at least the earlier 802 were somewhat optimisted as it had at least one dip down into the 3 ohm range. If so, the XA160 might have been cutting it too close.

As I said before, I prefer the sound of the SE amps, but if you really like your 802's, you'll love what the 600.5's do for them. However, if price were more of an issue, I definitely think you would find that the 350.5 has all the power you need.
That is an excellent review. I just upgraded my XA160s to the new XA100.5s and couldn't be happier. I just posted a review. I too find these amps very smooth and natural sounding. The .5's ability to double power at 4 ohms really helps drive the lower frequencies. Accurate timbre I think is their strongest quality.
Hi guys, I am looking into getting a XA-100 to replace my YBA amp for a different and perhaps 'better' sound. Problem is, I am also running it as a home theatre amp to my Meridian Processor and B&W N803 speakers.

Any advise if pure Class A will perform well in such a setup? Will it suffice for home theatre applications as well?
? for you: TAS said the XA 100s run cool for class A amps. not really sure if that means they only turn the room into a sauna instead of the inside of an oven. can you comment on heat output? what size room does it heat up? how hot the sinks are?
many thanks
I can only comment on the XA100.5s, not the XA100s. I think TAS was also talking about the XA.5s in their recent review. They do run less hot than the earlier Class A lines. I replaced my XA160s which were quite hot to the touch, though not as hot as the old Aleph series. The new XA.5s heat up my 16.5 X 17.5 X 7.5 room about 5 degrees warmer than the rest of the house now during the New England December weather. Not really a problem, I just turn down the heat in that room. The top plate is room temp, the heat sinks are warm to the touch but not hot. I can touch them for a few minutes without a problem. Last September during a warm spell the room was about seven to ten degrees warmer than the rest of the house and that was during a non-stop 200 hour break-in period playing music. I just cracked open a window. It's certainly not a reason to not buy them, unless you live in the South with no AC. They sound glorious.
Wow, so many glowing tributes on Pass.

I have the Maggie 3.6, with the dCS Scarlatti 3 box Dac/Pre amplification.

My room is quite small at 16 feet 11 feet 9 feet. (Making sure I don't misguide as meters are now the norm with many).

Would the Pass xa 100.5 drive the Maggie 3.6

I listen at fairly low to mid volumes.

Wow, so many glowing tributes on Pass.

I have the Maggie 3.6, with the dCS Scarlatti 3 box Dac/Pre amplification.

My room is quite small at 16 feet 11 feet 9 feet. (Making sure I don't misguide as meters are now the norm with many).

Would the Pass xa 100.5 drive the Maggie 3.6

I listen at fairly low to mid volumes.


The Magnepan website has a photo of 3.7's and XA100.5's.

I use the XA60.5's to drive my 3.6's in a larger room than yours, and have plenty of power. I almost never go out of class A.
has anyone driven a pair of dyns confidence C1 with pass x.5 or XA.5 series ?
If so what which series did you use and how did it sound pairing up with dyns ?