McGary Audio

Friday, April 3, 2009

Not A Separate, But Equal
Pass Labs INT-150 Integrated Pre/Amplifier

by John Gatski
  Although audiophile purists often scoff at the presumed sonic compromise of an integrated amp/preamp, I have always liked integrated amps for their convenience/performances quotient. I owned a late 1970s Onkyo A-7022 and sold new A7s and NAD integrateds in the early 1980s. Hi-fi buffs loved ‘em. They have gone in and out of fashion over the years, but a combined amplifier/preamp offers the advantages of simple placement and fewer cables, as well as audio quality that is only slightly less than separates. In many cases, you don’t hear a difference at all.   Case-in-point-is the new Pass Labs INT-150 integrated amplifier. In its essence, it is a combination of the XP-10 preamp and the X150.5 amplifier. But this excellent integrated is so much more — with not only its fine audio reproduction — but exemplary utility. Nelson Pass and Co. decided to build the integrated to satisfy a customer demand for a combo amp/preamp. The Asian market, according to Pass, loves integrateds and dealers have asked for a Pass model for a number of years. So have many US and European customers, he added. Now, the whole world can have a Pass integrated. Features   Priced at $7,150, the INT-150 is a full-featured integrated amplifier with Pass’ X- Series amp section and the signal path and parts from the XP-10 preamp. The INT-150 contains the now classic design Super- Symmetry amp design that Pass and his engineers developed in the early 1990s. Now in its third generation, the Class A/AB X.5 design utilizes carefully matched MOSFET output devices in a low feedback, fewer-stage configuration. All the important .5 improvements are here: ultra-linear JFET input devices, high-bias Class A on the input stage with limited feedback loop, (a feature adopted from the Pass flagship XA Series), better filtering on the power supply and more power supply capacitance. The .5 refinements are claimed to net better bass performance and transient response at lower distortion.   The XP preamp design is relatively new, but much improved over the last Pass Preamp designs. The stepped-volume control is more linear with its increased number of steps, especially at lower levels, and its measured noise and distortion have improved.   Feature-wise, the INT-150 input/output options make this unit suitable for nearly any analog connection option — audiophile or professional. It includes four stereo pairs of RCA single inputs and two sets of balanced XLR inputs. (Inputs 1 and 2 are RCA or XLR). And it contains one of my favorite features: preamp outputs. The INT-150 includes balanced and RCA output, though only one or the other is advised to be connected at a time.   The speaker binding posts handle spade and bare wire wire end quite easily, but not banana plugs. Since Pass hi-fi products are sold into the worldwide market, in which many countries prohibit banana plug connectors for safety reasons, that option is not added to their amps. If you have a favorite cable with banana plug termination, you will have to make adaptors. The back panel also contains the main power supply on/off switch and a central ground terminal.   The INT-150 front panels exudes first class craftsmanship with heavy duty brushed silver faceplate, blue backlit status display, blue LED input indicators, separate push-button input and mute selectors, and a push-button power switch. The very-authoritative volume knob feels wonderful. In fact, when the INT-150 warms up, the knobs gentle heat conduction provides a comforting warmth to the hand — like a heated seats warming up your torso in a luxury automobile.   For those who don't want to get up an feel the warmth — the heavy duty, sturdily constructed remote duplicates all front panel functions, plus adds balance adjustment.   Weighing in at 60 pounds, the INT-150 is about the size of an XA-30.5 amp in width, depth and length dimensions — with the same upwardly angled heat sinks on each side. There are no carrying handles. Spec-wise, the INT-150 outputs 150 wpc at 8 ohms and 300 wpc into 4 ohms With a bandwidth from 1.5 Hz to 60 kHz, (-2 dB). The damping factor is spec’d at 150 ref. 8 ohms nominal, and the slew rate, +/- 50V/uS. THD is listed at .003 percent at 5 watts output; no distortion was listed at full power. Overall specs, and subsequent listening, tests bear out that the Pass INT-150 is quite capable when dealing with high-resolution music.
  I placed the INT-150 in my primary audiophile listening room. I left plenty of room for ventilation, as the MOSFET designs yields plenty of warmth, but never too hot to touch. Speakers included Legacy Focus 20/20 HDs (previous generation), the new Canton Reference 9.2s, new Legacy Studio HDs and Lipinski L505s. For comparison preamps, I used a Rogue Audio Model 99 Magnum tube design, a solid-state Legacy/Coda high current preamp, Audio by Van Alstine Tube/FET hybrid and a Benchmark Media DAC 1 Pre converter/analog preamp.   Amps used during the preamp output listening sessions included Pass X350.5, Bryston 14B SST, Monster Cable MPA-2250 (it is indeed a pretty good amp), and an original Macintosh MC-275 tube amp from the mid-1960s. All audio was played through either a Esoteric DV-50 or Yamaha UDP-2500 Mk II universal player via internal DAC, or upgraded Benchmark DAC1 and DAC 1 Pre DAC. I used Alpha-Core balanced solid silver and Kimber Cable RCA cables; the speaker cables were also Alpha-Core — a pair of six-footer solid silver conductor with spades. All components were plugged into an Essential Sound Products power strip. The audition   Having used the X-Series for a long time, I was confident that the INT-150 would sound good, but its capability was even better than anticipated. The first thing I noticed was the revealing soundstage that Pass components are noted for — deep and wide sonic presentation with instruments well separated in the mix. The other obvious characteristic was the smoothness.   The original X Series preamps, and amps had a bit of coolness that could border on ragged with very dry recordings. The X .5 series and subsequently, the INT-150 do not exhibit that trait. For example, on the brilliantly bright EQ'd Fleetwood Mac “Rumours” DVD-A, the drum cymbals and acoustic guitar did not sound harsh as they have through other solid state amps.   Overall transient response of the INT-150 is exceptional. Drum cymbals exhibited the “in-the-room” spaciousness with the bits of subtle reverb inherent in most well-done recordings. Only the good amps can effectively relay those sounds without squashing the life out them. An example of the INT150's reproduction of these tones was the Elvis Presley’s “Suspicious Minds” from the Elvis "30 No. 1s” DVD-A. This particular version of the recording was mixed for this high-res discs with the cymbals more out in front, and the INT-150 really showcases the instrument. Uncannily real, my notes say. It was so good, I had another glass of wine and listened to the cuts six more times.   With the Pass, the transient energy of the AIX Records Lawrence Juber “Guitar Noir” DVD-A was sonically similar to my Pass X350.5 and Legacy Coda preamp reference system, but with just a touch more warmness. Again, the percussive sounds of fingerpicking, drum cymbals, etc. was very accurate. AIX Owner/Engineer Mark Waldrep does an amazing job recording jazz instruments in high-resolution formats and the Pass INT-150 reveals the extra sonic nuances embodied in those recordings. Even a picky audiophile — who demands separates — will be happy with the Pass’ ability to relay that kind of well-recorded music.   After two months of listening to numerous DVD-As and SACDs, as well as other high-sampling rate, home-brew jazz and acoustic guitar 24-bit audio recordings, I could not find any sonic defect with the INT-150. The wide and deep spacious image — with pin-point image detail, the tight bass, and a tinge of warmness across the middle — satisfied my sonic palette.   Different speakers added their own characteristics, but the essence was always there. I especially liked the Pass INT-150 with the new Legacy Studio HDs and Canton Reference 9.2 small speakers (separate review upcoming), and recommend either brand to mate with the Pass.   My favorite feature of the INT-150 is the separate preamp outputs — balanced or unbalanced. This audiophile connectivity makes the unit incredibly flexible. You can line out the stereo signal to a pair of powered subwoofers, or a pair of powered speakers in another room. Even professional mastering studios could use the INT-150 as a high-end control room pre/amp, then use the balanced outputs to run a set of powered speakers (or amp'd speakers) in another studio room. I really like its routing flexibility!   The preamp section is said to be virtually identical to the separate XP-10. I linked it with my other amps, and it sounded superb through all of them — even the warm-and-round original McIntosh MC-275. The MOSFET topology is a touch warmer than the Legacy and some other solid state preamps I have used, but it is the perfect complement to digital.   By the way, the INT-150 — whether through the speaker jacks or the preamp outputs — is amazingly quiet! No low-level hiss, buzz or any noise. And the multi-step volume control has no switching noise as you engaged a step at a time turning it multiple steps. A well-designed piece of hi-fi gear.   I had no real complaints with the INT-150. It could use a set of handles, 60 pounds is still 60 pounds. And I would prefer banana plug connections as well as spade terminals, but Pass amps are all banana plug-less. And it ain't cheap, but what finely-tuned, high-end U.S. made product is? The verdict   For many audiophiles, The Pass INT-150 is all you need for quality hi-fi. Those with small rooms who don’t want a lot of components and wires to arrange — this amp is perfect. It does not really compromise that much sonically, and it looks great in a small rack. Another consideration for those who have $7,000+ burning a hole in their pocket is a second room system. I could definitely see me installing this preamp/amp combo in my upstairs hone theater room for stereo hi-resolution music listening.   Professional audio studios and serious home studios also should give the INT-150 serious consideration because of its balanced pre-output utility and its accurate sonic delivery to passive speakers. Overall, the INT-150 rates our Stellar Sound! designation with great enthusiasm. I want one. And so does my neighbor. Visit for more information.

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