Pass Laboratories INT-150 Integrated
by Uday Reddy
For more than
30 years, Nelson Pass has established a first-class engineering reputation, initially with
Threshold Corporation and then with the company that bears his name, Pass Laboratories.
Pass also produces low-power amps under the First Watt name and supports the DIY community
with advice and project plans. To top this all off, hes a genuinely nice guy,
proving again that some people have all the luck.
||"The INT-150 is
quiet, with sonic images that emerge from a black background. The soundstage was rendered deep
and wide, with sound extending well beyond the outside perimeter of my speakers."
"However, one thing that I noticed right away was that the soundstage was more diffuse,
instead of the usual holographic, three-dimensional performance typical of most high-end
equipment." "The more I listened, the more I realized that this is what most live
music sounds like." "My only complaint with the INT-150 lay in one aspect of its
treble reproduction.... Through the INT-150, the upper registers of the piano sounded hard at
||"The INT-150 is a
minimalist integrated, with controls for power on/off, mute, input selection and volume.
Thats it -- no tone controls and no phono stage." "Essentially a Pass Labs
X-150.5 stereo amplifier mated to an XP preamp, the INT-150 incorporates technologies first
developed for the Pass Labs X.5 series of amplifiers." "The INT-150 will run in pure
class A, up to 13Wpc, thereafter running in class A/B to its full output, stated as
150Wpc." "All functions, including balance, can be controlled from the machined
aluminum remote control."
||"The first INT-150
that I had received was very cool-sounding and analytical for the first 24 hours, then settled
in with no appreciable change in character thereafter. The replacement was run-in at the
factory for 48 hours prior to shipping, with the result that none of the initial coolness or
analytical quality was apparent."
||"Whenever I review
a component, I consider the following situation: If what I own fails tomorrow, would I
consider the piece under review as a potential replacement? With the INT-150, Id have to
say the answer is a wholehearted 'Absolutely.'"
Having first established his reputation with
class-A amplification, Pass also produces class-A/B amps, and the company's current
production includes its first integrated amplifier, the INT-150. Essentially a Pass Labs
X-150.5 stereo amplifier mated to an XP preamp, the INT-150 incorporates technologies
first developed for the Pass Labs X.5 series of amplifiers. These include Super-Symmetry,
which produces high power and performance from simple circuits. The INT-150 is fully
balanced, another Pass design point, in order to take advantage of such a circuit's
ability to cancel out noise. Unlike the class-A, zero feedback amplifiers of the Pass XA.5
series, the INT-150 uses minimal feedback. The INT-150 will run in pure class A, up to
13Wpc, thereafter running in class A/B to its full output, stated as 150Wpc.
After spending the past 12 months reviewing
costly products with an average retail price of almost $15,000 USD, its nice to get
back to the real world -- sort of. The INT-150 is not inexpensive, but at $7150, its
certainly more affordable than the other integrateds I've been covering, though no less
Features and specs
The INT-150 is a minimalist integrated, with
controls for power on/off, mute, input selection and volume. Thats it -- no tone
controls and no phono stage. Rather industrial-looking compared to other Pass Labs
products, its still handsome, if a bit somber. The minimally sculpted front panel
has a centrally located luminescent display with large characters that are easy to read at
a distance and display the input selected and the volume level. Below the display, arrayed
from left to right, are the power button, mute button, buttons for four inputs and the
large volume control with a 63dB range in 1dB steps. All functions, including balance, can
be controlled from the machined aluminum remote control.
The upper portion of the rear panel has, from
left to right, RCA and XLR preamp output jacks, both RCA and XLR input jacks for inputs 1
and 2, but only RCA inputs for inputs 3 and 4. The lower portion of the rear panel has a
centrally located power button, flanked by an IEC power-cord receptacle and a fuse holder.
Rounding out the rear panel is a signal ground and horizontally arrayed left and right
plastic-shrouded brass binding posts. These binding posts have to be amongst the worst
Ive ever experienced. Because they are placed so low on the rear panel, only bare
wire is easy to use and banana plugs are not an option. Spade lugs, particularly on stiff
speaker cables such as my Transparent MusicLink, are very difficult to connect and have to
be inserted from above and tightened with a binding-post wrench.
The speaker binding posts led to a story. Two
weeks into the review period, the INT-150 went dead silent, even though it remained
powered up. Although I had been listening at reasonable levels, I suspected a blown fuse
and replaced it with one supplied with the amp. I was able to power up the amp once again,
but as soon it was fed a signal, the amp went silent within 5 seconds. The amp was shipped
back to Pass Labs and a new one was shipped to me, which worked flawlessly. Evaluation of
the initial unit showed nothing wrong with it after replacement of the fuse, and the
suspicion at Pass Labs is that because the binding posts are so close together, the spade
lugs must have come in contact with each other, resulting in a short circuit. As the first
instance occurred the day after my housekeeper had cleaned in the listening room, Im
assuming that she knocked the cables while cleaning behind the amp.
After hearing about Pass Labs suspicions, I
mentioned the poor design and layout of the binding posts and suggested a vertical array
like those on my Jeff Rowland Concentra. The good news is that Pass Labs liked my
suggestion so much that future production will have this improvement. Nelson, you know
where to send the royalty check!
The INT-150 is beefy both in power output and in
dimensions. Rated at 150Wpc into 8 ohms and increasing to 300Wpc into 4 ohms, the INT-150
should have no problem driving most speakers. Frequency response is rated at -3dB from
1.5Hz to 60kHz. Slightly wider than a standard rack width, the INT-150 measures 19"W
x 7"H x 19"D and weighs 60 pounds, giving you a tangible sense of owning
something for your hard-earned money.
You'll want to give the INT-150 plenty of space.
Although its amplifier section runs in class A/B amp, it still gives off plenty of heat.
Its sleek, widely spaced heat-sink fins and top plate never got too hot to touch, but the
unit still ran hotter than any other amp Ive had in my room, so much so that there
was a noticeable difference in temperature whenever I walked into the room and, with
prolonged listening, I had to crack a window open to let the warm air vent out.
The first INT-150 that I had received was very
cool-sounding and analytical for the first 24 hours, then settled in with no appreciable
change in character thereafter. The replacement was run-in at the factory for 48 hours
prior to shipping, with the result that none of the initial coolness or analytical quality
was apparent. Apart from the hiccup with the first amp, I had no further problems.
Like most well-designed integrated amps, the
INT-150 is quiet, with sonic images that emerge from a black background. The soundstage
was rendered deep and wide, with sound extending well beyond the outside perimeter of my
speakers. Given the narrow width of my listening room, this was not only a pleasant
surprise but also certainly better performance than that of any of the other amps that
However, one thing that I noticed right away was
that the soundstage was more diffuse, instead of the usual holographic, three-dimensional
performance typical of most high-end equipment. While certainly not veiled or gauzy, this
was atypical of my experience with other integrated amps, which have more of a laser-like
focus. At first I found this a bit off-putting, but the more I listened, the more I
realized that this is what most live music sounds like. Unless youre sitting in the
front row of a jazz club or next to the orchestra section of a concert hall, much of the
sound is going to be reflected, which seemed exactly the kind of perspective the INT-150
provided. Once I got used to this, I enjoyed it and found myself listening more to the
music alone, paying less attention to the placement of musicians and their instruments
within the soundstage.
Loudspeakers Wilson Audio Sophia.
Integrated amplifiers Jeff
Rowland Design Concentra, Luxman L-509u.
Digital Wadia 830 CD player,
Logitech Transporter wireless DAC, Apple MacBook with 1TB Apple Time Capsule.
Audio Ultra MusicLink.
Speaker cables Transparent
Audio Ultra MusicLink.
Headphones and Headphone amplifier
Sennheiser HD 600 headphones, Ultimate Ears UE 11 Pro in-ear monitors, Ray Samuels
Audio Emmeline, The Predator headphone amp.
Accessories Audio Power
Industries Power Pack II.
Ive often noted when evaluating a component
that once I get used to its sound, Ill favor one type of music over another with it.
Because I listen mostly to jazz these days, I was quite surprised to find myself listening
to a lot of rock'n'roll and jazz fusion with the INT-150. Because rock recordings are
usually overly compressed, I find them fatiguing after just and hour or so and end up
switching over to jazz or classical music. With the INT-150, I could listen for longer
periods and derived more enjoyment from the experience. Ive been a fan of the Black
Crowes since their debut release and have kept buying every album, hoping that
theyll equal or exceed the work on their sophomore release, The Southern Harmony
and Musical Companion (American Recordings CK 69398). "My Morning Song" is a
harmonically dense, grinding jam with layers of sound. The INT-150 handled this track
well, without breaking a sweat and showing no congestion or loss of clarity, even at high
volumes. And when lead guitarist Marc Ford tears into his ecstatic, sinuous solo, it was
relayed distortion-free (except for whatever distortion Ford was adding to it, of course).
One night, while my wife and daughter were out of
town, an audiophile buddy and I spent many hours drinking beer and listening to one Stevie
Ray Vaughan album after another. Like his hero Jimi Hendrix, Vaughan had monster chops but
a lousy singing voice, flawed with slurring and lack of enunciation. The INT-150 did
nothing to improve this, but it did seem to de-emphasize these qualities so that they were
less noticeable. More obvious was the reduction in the stridency of his voice, readily
apparent on "The Sky Is Crying" from Blues at Sunrise (Epic/Legacy EK
63842). I have always loved this tune, but the singing was somewhat grating to me. Via the
INT-150, this grating quality was softened ever so slightly, easing the rough edge. Lest
you think this was due to "beer ears," rest assured this result was still
present with repeated listening. This improvement in Vaughans vocals would seem to
indicate some softening in the midrange, but I didnt notice anything particularly
wrong with the midrange, which was tonally neutral with no perceptible sonic character.
Dynamically, the INT-150 performed strongly,
especially with large-scale orchestral recordings, in which the momentum of the piece was
preserved, even in quiet passages. On the "Mars, the Bringer of War" section
from Gustav Holsts The Planets played by the Philharmonia Orchestra and
conducted by John Eliot Gardiner (Deutsche Grammophon 445 860-2), the piece begins with a
low-key but incessant march that builds to a cacophonous crescendo. This brooding sense of
impending disaster was captured perfectly, the INT-150 never having to strain.
However, the INT-150 was quite capable of being light on its feet when called upon. On
"Jupiter, the Bringer of Jollity" from the same recording, the opening fanfare
gives way to a flowing melody that feels joyous and hearty, then segueing into a dainty
and delicate segment through which the INT-150 conveyed the works innate gaiety.
One of the reasons that I preferred rock and jazz
fusion with the INT-150 was due to the integrated's forceful bass output. Like Brian
Bromberg, Christian McBride is a monster bassist, with both acoustic double bass and
electric bass guitar. On Chick Corea and John McLaughlins Five Peace Band Live (Concord
Records CRE-31397-02), McBrides playing is propulsive, and the INT-150 highlighted
this quality, capturing his ability to anchor the bottom end and flesh out the rhythm
My only complaint with the INT-150 lay in one
aspect of its treble reproduction. As Ive mentioned before, I listen to a lot of
jazz, especially piano-trio recordings. Through the INT-150, the upper registers of the
piano sounded hard at times. I am at a loss to explain why this was the case only with
piano when all other aspects of the INT-150's treble were reproduced cleanly and with fine
detail. Also, why was this accentuated more via the INT-150 as compared to my Jeff Rowland
Concentra and all the other integrated amps Ive evaluated over the past year?
Perhaps different cabling would have made a difference.
As I mentioned, I really enjoyed the bass
reproduction of the INT-150. Although it didnt have quite the bass control of the
Luxman L-509u ($10,500), the best Ive heard yet, it was at least as good as that of
my Jeff Rowland Concentra ($5600 when available) in many respects and exceeded the
Concentra when it came to the tunefulness and ability to follow the bass lines. While both
the Concentra and the INT-150 are tonally neutral, the Concentra leans more toward the
warmer side of the spectrum in the midrange, but I didnt feel that the INT-150
suffered in comparison. I did prefer the treble of my Concentra, which was more liquid and
tubey in its quality, but the INT-150s ability to reproduce the upper frequencies is
still comparable -- with the one caveat regarding the upper registers of the piano. Even
if you listen to a lot of piano jazz or piano concertos, I dont believe this
character is a deal-breaker. Still, careful system matching and cable selection are
Despite my reservations with regard to piano
reproduction, I thoroughly enjoyed my time with the INT-150. As for its presentation of
the music, I really came to appreciate the INT-150s more diffuse staging, and I
suspect that others will enjoy this too. You just have to give it time so you can get used
to the perspective, which, to my ears, replicated the live experience in an obvious way.
And heres something else. Whenever I review
a component, I consider the following situation: If what I own fails tomorrow, would I
consider the piece under review as a potential replacement? With the INT-150, Id
have to say the answer is a wholehearted "Absolutely."
|Pass Laboratories INT-150 Integrated
Price: $7150 USD.
Warranty: Three years parts and labor.
P.O. Box 219, Foresthill Road
Foresthill, CA 95631
Phone: (530) 367-3690
Fax: (530) 367-2193