Review: Pass Laboratories XA100.8 mono block amplifiers











“The Pass Laboratories 100.8 mono block amplifiers mark the advent of what may be the finest-sounding amps the company has produced to date, and a solution that is fully competitive with the very best on the market today.” — Scot Hull

“Solid state like this would have been unimaginable just a decade ago. The Pass XA100.8 is a new benchmark for versatility and performance. Everyone should have a chance to hear a pair. It’s almost enough to make me swear off tubes.” — Malachi Kenney

Passing Muster

The Editor Himself gave me a call in late August to ask whether I’d be interested in reviewing what he deceptively called “some Pass gear.” Since I’d just gushed about listening to the new Pass Laboratories XA60.8 at this year’s California Audio Show, I may have said, “yes,” before he finished the question. A couple of weeks later, on the hottest day the Oregon Coast has seen since I moved here, two boxes — each pushing 120 pounds — showed up. Inside each, and fresh off the assembly line, was one XA100.8 monoblock.

That’s when the Editor Himself called again. Would I be interested in comparing the .8 to some of the .5 series? And would a Pass preamplifier be interesting for color? I may have been slower to answer that question, but, like a chump, I said, “Sure.” A week later, a three-man crew from FedEx showed up with five more Cartons of Unusual Size, and a whole mess of hand trucks to wheel them up my driveway.

“Next time,” the driver said sternly, “call UPS!”

That’s when I called The Editor. “I literally don’t have the space in my house for these,” I moaned. “My garage is full of giant boxes,” I complained. “My back! My back!” I pleaded. The Editor himself called me a crybaby. I was directed, in no uncertain terms, to “suck it up.”

The “it” to be sucked, in this case, was a pair of XA60.5 monoblocks, a pair of XA100.5 monoblocks, and a wholly absurd XP-30, three chassis preamplifier. I mention this to you because you might one day get a phone call asking if you want to review “some gear.” If that happens, make sure you ask for a very clear definition of “some.” You want to be very certain that “some” isn’t too semantically close to “all.”

The Pass Labs XA100.8

The main subject of the review, though, is the Pass XA100.8 amplifier. Weighing in just over 100 pounds per channel, standing at just under ten inches tall, and extending just under two feet in length, it could be described as comfortably smaller than some of the Dreadnought Class amps Pass produces. It could also be described as a hulking behemoth that dwarfed any other electronic gear in my house and was outweighed only by my refrigerator.

Extensive heat sinking on both sides accounts for some of that weight. Pass has abandoned their Terminator-esque faceplates in favor of a more restrained (and adult) styling that shaves a few pounds off the front of the amp. Centered on the faceplate is, of course, the Big Meter and a push-button switch to take the amp out of standby mode. The rest of the amp is a nondescript, completely utilitarian steel that, other than its superbly close fit, gives the distinct impression that every reasonable expense has been spared. The money — and the weight — is inside the box. The only bling is that faceplate.

Moving around to the back, the other sign that these amps cost a cool $19,300 per pair is a pair of torque guard binding posts on either side. RCA and XLR (jumpered for single-ended operation by default) inputs top the back panel, with an IEC inlet and power switch down at the bottom. Rounding things out is a set of binding posts for the 12v trigger, and (since these amps have a differential output) what appears to be a post for a ground connection. You could consider that ground useful for your Tannoys‘ fifth binding post, or you could consider it an easy connection that lets the amp’s differential output stage connect easily to a subwoofer (like REL) that can’t take a balanced signal as an input.

The main binding posts deserve special attention. I’ve long been a fan of Speakon connectors for their no-muss-no-fuss user friendliness — those of us with ten thumbs need all the friendliness we can get — but the ones I’ve heard have had a tendency to affect the sound in not terribly attractive ways. The Cardas Patented Binding posts have been my go-to for a good, solid connection that rivals a simple screw terminal while still offering some ease of use, but their spade-only compatibility, and my habit of dropping pieces of the connector into some dark crevice when swapping cables, limits their attractiveness. Whoever supplied Pass with these five-way binding posts now has my undying loyalty. They’re chunky, they feel good, they’re well spaced, and they’re impossible to over tighten. Just twist them until they make a ratchet noise. Done. These things are so good that I didn’t even swear once when I used them. That is, for the record, a first.

Burn in takes on a new meaning

I mentioned that the amps arrived on the hottest day of the year. In case you ever get jealous of the audio reviewer gig, I want you to remember that. Air conditioning is an unheard of frippery in grey and rain-soaked Lincoln City. The Pass amps arrived during a freakishly hot period of sunny days in the nineties and warm nights in the high eighties.

People, these amps suck 450 watts each from the wall and heat up to about 130 degrees Fahrenheit. Temperatures in my house quickly passed 100 degrees and stayed there.

On top of the heat, I feel it necessary to mention the break-in smell. These amps were brand spanking new. That means the odor of new electronics cooking in the summer heat was … let’s call it “oppressive.”

In this case, though, this can be seen as a good thing. The amps required a significant amount of use before they finally came on song and the smell turns out to be a good indicator of how much of a flogging you’ve given. When it finally disappears, make a note. You’re 50% of the way toward being completely broken in.

You’ll want to make that note. Break in with these is a very big deal indeed. The sound when the amps were fresh out of their factory boxes was, barring a few complaints, magnificent. Two days later, that sound was discordant. During the six weeks it took to finally run in the amps, the sound careened around like a drunken toddler. There were days with no bass. There were other days with no treble. Those were both better than the days with no midrange. There were even days with bass, treble, and midrange — but each one of those was wrong.

Everything evened out at about week three, but there was a persistent (and annoying) sense of a double-tap on the treble. Higher frequencies seemed to have an echo. It was, in fact, the only constant throughout the break in period. I had even started drafting a review that referred to that as the fatal, tragic flaw of the amps while trying to describe why I loved them anyway.

And then, in week six, the double-tap went away. I didn’t even notice it at first, because I thought someone had broken my window.

I should explain something. My listening space, in violation of all good sense, has an eight foot wide window on the front wall. It does terrible things to the sound, but I consider that a good trade for the chance to watch deer walk by less than fifteen feet away. I should also mention my general antipathy to solid state. Most of the solid state I’ve heard — all of it, honestly — misses a little something. Heck, every amp misses something, but there’s a stereotypical solid state sound that misses depth.

The moment that the amps broke in, the soundstage jumped through that window.

The Sound

Half of Groovin’ with Jug may be the best album ever. The other half of it is genuine elevator pablum, but half the album is a treasure. Richard Holmes and Gene Ammons just couldn’t find the magic when they were in the studio (the pablum). They could, however, drag the microphones back to a club and hammer it out on stage (Holy Fried Awesome!). The live takes on the album are, in a decent system, only about seventeen ashtrays away from being as close to there as you’re likely to get.

Before the 100.8s broke in, that meant a soundstage that extended out well past the side walls and from the front wall up to the couch. When they broke in, while I was sitting at my kitchen table, it meant that the phone was ringing in my garage, glasses were clinking at my kitchen sink, and Jug was blowing about four feet up on the hillock outside my big front window.

Was it as purely holographic as the very best tube soundstaging? No. Was it realistic soundstaging? It was sure as heck closer to it than my Manley Snappers. Did it have that thermionic breath-of-life tone? I didn’t think so, but I honestly couldn’t tell at first. More music was called for, but my wife, damn her, was stern. She got the sweet spot when she was at home, and I could fend for myself.

“You write the review, then!”

“No,” she explained.

So we descended into Americana for a while. Patty Griffin’s “Moses” is almost the Ur girl-with-guitar track. The Pass XA100.8 put the guitar in the room. Most decent amps do well with the tone, but fall short of making the illusion’s dynamics believable. These monsters from Pass more than managed to cross the line into total illusion. There was no sense at all that dynamics were being truncated, though I will admit that I wished that Patty had chosen to belt that number out in someone else’s house.

First Aid Kit’s “Emmylou” showed the sisters’ impeccable harmonies as flawlessly and properly layered, but they really surprised by showcasing producer Mike Mogis’s slide guitar work. Another run at the Mekons’ apocalyptic “Burning in the Desert Burning” had the Pass amps not only pulling apart the band’s campfire chorus, but highlighting the minimal vocal reverb that turns John Langford into the voice of happy doom.

I left the room when Kirsten cued up Rufus Wainwright, but she told me that it was “really good.” I consider that to be a strike against the amps. Let me know when someone with taste makes an amp that refuses to play that stuff, will you?

Fortunately for me, Kirsten left the house occasionally. That’s when Ministry showed up (accompanied by Portishead, Shilpa Ray & Her Happy Hookers, the Clash, the Minutemen, and Crazy Horse). It didn’t take long to be sure that the XA100.8 knew know how to rock like a seventeen year old with a stolen bottle of Jack Daniels. For reference: playing the version of “Cortez the Killer” hiding out as “alternate take” on the hi-rez version of Psychedelic Pill makes the best argument for big amps and big speakers that I’ve ever heard. If you’re going to yank the volume knob all the way to the right for one track this year, make it that one. If you can make it through without cheering, something has gone very wrong with your life.

The XA100.8s are clearly heavyweights, but there’s always a question about whether a prize-fighter can also be delicate. There’s no worry here. These are as delicate or as energizing as you need them to be. Whether its refined contemplation of Gidon Kremer and the Astor Quartet on their Tango Ballet, or the exuberance of Barbara Hendricks hollering out “When the Saints Go Marching In” on Chants Sacrés, the Pass amps were chameleons. I never found any music that wasn’t served superbly. As someone who enjoys complaining a great deal, I feel a bit cheated.

Were there shortcomings? Yes. Maybe. The treble was just a notch or two less pure than the very best I’ve heard, the depiction of space wasn’t up there with some exotic single ended triodes, although I can’t think of anything else that bettered it. And there was that lingering problem of the heat and power consumption of running two rather large Class A monoblocks.

Warmup is, unsurprisingly, another issue. You’ll want to make use of that standby switch. The amps only take an hour or so to really hit their stride when they come out of standby. Turning them off, though, is an entirely different story. You’ll be looking at more than a day before they’re singing again after being powered down for any length of time. That’s not a shortcoming, really, but I’m reaching here. There’s not a whole lot to complain about.

System matching wasn’t a weakness at all, though. Everything from a Mark Audio 10.2 single driver, some Altec 604-8g, Tannoy Glenairs, old Martin Logans, or the under-the-radar, over-achieving, Endeavor Audio E3 gave the best, most even, most well-rounded presentation I’ve heard from any of them. As far as I can tell, the XA100.8 is an easy match for speakers. Preamps and sources provided any desired character, with my Frankensteined K&K preamp providing the most tonal density and the three-chassis Pass XP-30 providing freakish transparency. Single ended inputs worked just about as well as the balanced inputs, with only a slight diminution of the outer envelope of dynamics and a slight rise in the noise floor (unobjectionable even sitting in the nearfield of of 100db Altecs) as the tradeoffs. In every way other than physical size, these amps are exceptionally easy to fit into a system.

Trying to get a handle on what the XA100.8 actually sounds like is the kind of problem that highlights just how very good these amps are. When I had the amp paired with the Tannoy Glenairs, I would have told you that the amps’ signature was “big, bold, and authoritative”. They were bruisers with a propulsive kick that communicated every musical line, never sacrificing musicality for Hi Fi stunts. Hooked up to the Endeavor E3, though, the 100.8 was a critic’s favorite tool, digging detail out of the mix like a paleontologist brushing dirt away from a fossil. Musical, yes, but almost incomparably incisive and insightful. The old electrostats, on the other hand, showed the amps as speed demons. Quick transients and micro-detail were their specialty. Every listening session became a deeply intimate affair.

What every presentation had in common, though, was impeccable evenness and timing. The musical flow was never disrupted by any oddity. There were no missteps, there were no weak beats, and there were no favorite bits to be found. Where some amps will highlight the vocal range, and other amps will impress with their sense of air, the XA100.8 will simply serve up whatever delights are on the menu so the listener can decide what is important this time. They are stunningly natural amps that deliver the music in a stunningly natural way. Listening to them isn’t so likely to make you reach for every album in your collection as it is to make you listen to whatever it was that you just heard again and again and again.

If you have the cash and the cooling, the Pass XA100.8 monoblocks are no brainers. They’re so versatile and rewarding that it would be hard to praise them enough. They’re not cheap at $19,300 per pair, but they are superb and uncompromising references.

These will be end-game amps for all but a very few.

Play Time

The Editor had been giving the eye to the XA100.5 ($16,500 per pair) and the XA60.5 ($11,000 per pair) as well as that XP-30 preamp ($16,500 per pair). They came to my door with the hope that I could shed some light on the differences between the amps while talking about any system synergy. I honestly wasn’t expecting much in the way of differences when they showed up. I was unbelievably wrong.

Let’s start with the preamplifier first. It’s magnificently built, startlingly intuitive, sports an honest-to-goodness mono switch, and comes with a milled remote that’s solid enough to use as a mêlée weapon. It features what has to be one of the most transparent volume controls that I’ve ever used. It’s even-handed, with only a bit of solid-state sheen at the top end and a surprising bit of leanness in the mid-bass and lower mids. The master volume knob is large enough to find in the dark — in a parking garage. When you’re lost. On the moon — and comfortable enough that you’ll probably want to use it instead of the remote just to giggle when you do. Each signal channel has an independent gain control, so balance adjustments are possible, too. I can’t think of any feature that wasn’t provided for.

There’s nothing bad to say about it, but rambling on about “competent and transparent” doesn’t make for good reading in a review. It’s superlatively competent and transparent, of course. It does, after all, cost as much as a new car. Nobody lucky enough to afford one will feel shortchanged.

The curiosity of the bunch is the highly praised XA60.5. The amp has earned its reputation. The treble is, bar none, the sweetest and cleanest that I’ve heard. Soundstaging is beyond reproach, offering a nearly Platonic sense of space and a fully realized view into it. There’s none of that “Oh, it’s good for solid-state” faint praise to be found here. Imaging was wholly holographic and completely captivating. Tone was everything you could hope for, uncolored and unromantic, but properly dense and with full bloom. The amp’s speed was something I never expected, though. It had the magical property of turning my big, slow Tannoys into lightning fast Lowthers — but with great treble! It was a Christmas miracle!

Unfortunately, the XA60.5 also turned my big, slow Tannoys into lightning fast Lowthers in a less endearing way. It’s just weak below 500hz. By the time you get to the sub-100hz region, it’s only going to offer a faint representation of bass. This trait held firm on every speaker I used, changing all of my big boxes and big panels into surprisingly dynamic shoebox monitors. Kick drums had kick, but no body. Nick Cave sounded a bit like a choir boy. The Anonymous 4 sounded wonderful, but I got the impression that the Tallis Scholars were an all-girl band. My lousy pressing of Black Market Clash never had any bass to begin with, so it sounded better than I’d ever heard it.

The listening experience was, in other words, A Little Weird. I was listening to what was, in essence, my favorite amp ever, but I couldn’t see this bringing the best out of my systems. The 100.8 couldn’t quite match the treble performance of the 60.5, but it was very close in the running, and it was a much better all-rounder.

The XA100.5, as the previous incarnation of the 100.8, promised better things. It mostly delivered — turning my Tannoy Glenairs into bass monsters. In fact, it delivered just about the best bass performance I’ve heard in my room. If it was slightly plummy — and it was — it was euphonically so. If it was slightly less dynamic than the 100.8 — and it was — it didn’t seem like much of a shortcoming. The bass was wholly addictive, ridding me of any desire for subwoofers. Pairing it up with the ever-so-slightly-lean XP-30 preamp quickly eliminated the extra fat (SYNERGY!), leaving me with a system that could do full justice to the Telarc 1812 when I wasn’t too busy cueing up every Mingus album in the house. Listening to Duke Ellington’s Afro-Bossa through this system remains one of the high points of my time in this hobby.

But you know what’s coming, right?

The treble … It wasn’t great. It was very solid-state sounding, with sheen and glare aplenty compared to the other two Pass models in the house. On top of that, everything between 1500hz and 10khz seemed touched by euphony, making completely crap albums (Black Market Clash, again) sound wonderful. It effectively homogenized the system with its own stamp, reducing the differences between cables, preamps, sources, and even my moods. That’s before we even talk about the soundstaging, which was so stereotypically solid state in character that I felt like I was suffering physical withdrawal after listening to the XA60.5.

Which got me thinking. The 60.5 and the 100.5 have just about the same gain. What would happen if I biamped the Tannoys with the 60.5 on top? What would happen if I used the XP-30 to match gain and ran the 100.5 on the bottom?

What happens is something very close to an expense paid visit to Paradise. With only minor differences in voicing, the whole system gelled. Treble that slightly bettered the 100.8 was matched to bass that dug slightly deeper than the 100.8. The slight difference in voicing between the amps was eventually an annoyance and distraction in this quick-and-dirty setup, but, during the four hours or so it took to notice that, I was treated to what was some of the best sound that I’d ever wrung out of any Tannoys. It quickly became clear, though, that the 100.8 alone provided a much more cohesive presentation. It was less colored than the 100.5, having a more realistically live sound in the lower frequency ranges while coming within spitting distance of the 60.5’s unimaginably good high-end performance.

In other words, the $19,300 pair of XA100.8 were, in my room, far preferable to $44,000 worth of Pass’s previous generation of gear powering the system. I stopped thinking that Pass had raised the price of their 100 watt amp and started realizing that they’d managed to lower the cost of absolute performance.

Which is really kind of neat when you think about it.