Review: Pass Labs INT-250

Pass Labs’ INT-250, of all the audio gear I’ve had the pleasure of auditioning in my system, is perhaps the most challenging in the pulmonary sense. Weighing in at a hefty 105lbs it reminds me of my days slinging buckets of concrete on survey and construction crews. The heft would be more manageable if the aforementioned Pass’ flanks were not made of some of the sharpest heatsinks I’ve ever felt – throw a tomato at this bad boy, you’re likely to get a perfectly sliced caprese salad. Helpfully, the unit has two pro-audio style handles on the back, which make handling a little easier, but I enlisted some aid from a friend to drag the unit into place.

Pass, as many of us are familiar, is famous for Class A and Nelson Pass’ circuit wizardry. I think it’s unfair however not to point out the exceptional attention to detail and design which goes into their units as well. The INT-250 ($12.5k) I reviewed was beautiful in a sort of ‘Robo-cop settles down and has kids’ way, the front panel is almost as thick as my wrists, and even the side panels are supremely sturdy. Inside, the unit is stunningly well laid out, and from the gorgeous and ultra-smooth Furutech speaker taps on the back to the comprehensive remote control, every quality of life factor is taken care of.

Pass also supplies a factory checklist of various parameters, signed by not one, but two factory techs. The unit comes double boxed, impeccably packed, like an enormous, aurally exciting and prickly cyborg hedgehog. Function-wise about the only thing not covered by the Pass INT-250 is use as an external amp only, as it lacks post-preamp inputs. Otherwise, it can function as an integrated or a preamp, and the inputs and outputs supplied are adequate for either of those duties: a set of XLR and RCA preamp outputs, as well as 4 inputs, two with both XLR and RCA inputs and three more which are RCA only.

Sound Impressions

On to the really interesting bit however, the sound. When it comes to Pass Labs, many of us are familiar with the reputation in theory: solid state, Class A, exceptional sound that no one has ever really said a bad word about. In a way, there’s a reason for this, and the INT-250 does this and more – it backs it up with immense beef, enough to drive even the most punishing loudspeakers. On first firing up the Pass INT-250 in my system I’m greeted with a sound I can only describe as ‘classy.’ Things are holographic, airy and with a sense of space that seems to reach up into the ever elusive ‘height’ dimension of two-channel stereo. There isn’t a ‘haze’ or lack of detail as some MOSFET solid-state amps seem to have, but neither is any hint of that rigid and edgy JFET sound that some solid states seem to have. One might rightly term this a kind of ‘warmth’ and often Pass Labs gear gets compared to tube gear in this regard.

Unlike tube amplifiers I’ve heard in my system, the pass does not seem to layer sounds on the Z-axis of depth, where front-back gradations are flensed out in a high degree of detail. Instead the Pass seems to work with a slightly rounded depth to its soundstage and a sort of layering of width. Elements are perceptually quieter, but seem to emerge from a sort of uniformly charged sense of spatial cues. When a record starts or a digital track begins, the Pass immediately fills the room with a very damped but electric sense of stereo ​energy​. Depth is still well presented, but my attention is drawn to the spatial cues ​around​ instruments and voices, rather than their closeness of distance from me, which is something tubes seem to do more. Neither is bad, nor less precise, simply different flavors.

However, if that sounds like a slight indictment of the Pass’ portrayal of depth, let me clarify it is not at all. If the recording contains depth or spatial cues, you will absolutely hear them in perfect detail, perhaps even sometimes a kind of warm, laid back and enveloping way that almost flatters bad recordings but never feels untruthful. Everything the INT-250 does is relentlessly pleasant and listenable, yet incredibly quiet, and detailed. The sensation of a ‘black background’ and exceptional damping factor with an amplifier that puts out 250W is present even when using the INT-250 only as a preamplifier, a use case in which it performed exceptionally.

However this is also perhaps the only truly objectionable trait of this amp, and itsn’t even a fault, merely trait, and a matter of taste. There is other gear in my collection, some solid state, some tube, which does have greater clarity than the INT-250. The Pass always gave me a sense that I was experiencing the space of the recorded event, that ‘you are there’ facsimile, rather than the ‘it is here’ illusion. As a matter of taste, I tend to prefer the latter, but it’s a great credit to the Pass that I found it so pleasant sounding even ​despite​ my preference. You could grab a blanket and take a nap in the INT-250’s soundstage, it’s just that spacious and cozy.

Speaking of this preference however, what the Pass brings to the ‘you are there’ experience is second really to none, and if you were to tell me I had to live on a desert island with only the INT-250 as my amplifier, you’d hear no complaints from me. I have a sense that the Pass labs gear has been meticulously tuned by incredibly clever engineers and listeners, who have spent years tweaking, tuning and listening. My thoughts even deep into my listening sessions with the amp were simply that every possible annoying trait or tiny irritation has been manicured out of the sound. Hi-fi reviews really are delightfully fun when you get to play with gear of this level, where there are no real faults to find, only matters of taste. Bass is subterranean, there is the slightest silkiness and smoothness to the midrange and treble which gives music an addicting density and richness without actually betraying any harmonic distortion or lower-midrange bloat that can sometimes accompany THD. Everything the Pass does is transparent, yet also also painted with a subtle liquidity that always lets you know you’re listening to a Pass, and yet if you try too hard to listen for it, you simply get drawn into the detail of the music.

Design-wise, the Pass INT-250 as far as I can tell is a real all-in-one solution for someone who wants everything Pass labs has to offer, in a package that can drive anything. The price is high, but not as exceptionally high in Pass’ catalogue. In fact, given their average prices, the amount of power on offer is actually about as cheap per-watt as you’ll find in the Pass Labs catalogue. But no matter how hard I tried, I never could get that little blue dial on the front to move far enough to indicate I had exited the class A bias range. Even blasting tunes into the 90 and close to 100dB range with earplugs in with inefficient speakers, I never got it to move even close to that Class A/B part of the meter.

Summing Up The Pass INT-250

If the INT-250 were a city, it would be Vancouver. You can’t argue with anything about it, it is nice​ in every possible way. It may be that I’m a little too crass for nice however. I like a little junk, a little grit in my audio. In other words, show me the Plankton. But even with my taste for a slightly brasher sound, I have to admit, the Pass Labs had me hooked while it was here. As I stated before, if I had to live with an INT-250 for the rest of my life (and that’s currently looking like a pretty long time) I would have absolutely zero complaints. It’s a high-end product and amplifier in every way, and even with my tastes resting slightly to the left of it’s exact signature, it’s such a beguiling amplifier I’ll be sorry to part with it when it inevitably needs to get sent back. I ​will m​iss it, and it ​will​ cast a shadow over future gear reviews, with that nagging little ‘but is this as good as the INT-250’ voice in the back of my head. I’m not sure of many things in life, but the Pass Labs INT-250 is reference quality gear in every way, of that I ​am​ sure.

By Grover Neville

More info: Pass Labs

Pass Labs’ founder Nelson Pass has some interesting viewpoints on audio and amplifier design. You can find an in-depth review with him on The Occasional Podcast’s Season Three Finale on iTunes, Spotify, the embed below or anywhere you download your favorite podcasts.