Pass Labs HPA-1 Stereo Preamplifier/Headphone Amplifier Reviewed

Published On: September 4, 2017
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Pass Labs HPA-1 Stereo Preamplifier/Headphone Amplifier Reviewed

In this week's featured review, we explore the HPA-1 from Pass Labs. The HPA-1 is a solid-state analog stereo preamplifier and a headphone amplifier with an MSRP of $3,500.

Pass Labs HPA-1 Stereo Preamplifier/Headphone Amplifier Reviewed

By Author: Terry London

Terry London has always had a great passion for music, especially jazz, and has amassed a collection of over 7,000 CDs covering the history of this uniquely American art form. Even in his teenage years, Terry developed a passion for auditioning different systems and components to see if they could come anywhere close to the sound of live music, and has for the last forty years had great fun and pleasure chasing this illusion in his two-channel home system.
Terry is a practitioner of Rational Emotive Behavior Therapy by day, and runs the Chicago Institute for REBT. He has also authored nine books on this of type psychotherapy and education.

For over 30 years, I have exclusively used tube-based preamplifiers in my two-channel reference system. I have also used some of the most historically acclaimed active solid-state line-stages (Threshold FET-10 and Mark Levinson no. 32), along with two highly regarded passive line-stages (Placette Audio Vishay S102 resister and Bent Audio audio-transformer). Based on my personal taste, I have come to the conclusion that they all lacked two critical qualities compared with tube-based preamplifiers.

First, none of them could create the gorgeous colors/timbres found in live performances as successfully as the finest NOS input/signal tubes (12AU7/12AX7/6SN7/12SN7/12AT7). Second, the solid-state line-stages’ handling of spatiality--such as three-dimensional imaging, air, and space around individual players--and their ability to create a holographic soundstage was not up to the same level as the finest tube-based designs. These shortcomings were always apparent to me, regardless of whether I used solid-state or tube-based amplifiers. Some will argue that a preamplifier should be a “straight wire with gain,” not adding or subtracting anything from the signal, but I fall into the camp that the addition of positive sonic traits by a line-stage is fine as long as it does not become euphonic and exaggerated to the point of being unrealistic.

In the time I have written for, I have done six stereo preamplifier reviews, all of which were tube-based preamplifiers. After my review of the tube-based Linear Tube Audio MicroZOTL2.0 headphone amplifier/preamplifier last year, I began to receive requests from readers asking if I would I review a solid-state preamplifier--one that is relatively low in cost that might come close to the performance of the best tube-based designs that I had previously reviewed. I decided on the Pass Labs HPA-1 headphone amplifier/preamplifier, which turned out to be a sonic gem when used as a line-stage.

The HPA-1, which retails for $3,500, is the first headphone amp/line-stage that Pass Labs has ever built. The HPA-1 weighs 15 pounds and is 3.5 inches high by 11 inches long by 12 inches wide. Like all of the company’s gear, the external materials and internal parts are top notch. The HPA-1’s thick front plate matches the look of the current Pass Labs .8 amplifiers and standalone preamplifiers. The power supply/transformer is so robust that it could easily be used in a power amplifier. The HPA-1 uses a Class A MOSFET output stage, which ensures that the line-stage will drive any amplifier with high-level resolution. On the front plate is an LED that indicates when the HPA-1 is turned on. Pass Labs recommends you leave the unit on all the time, so they have placed the on/off switch on the back. There are three push buttons to engage the line-stage section and to switch between two inputs. Underneath an engraved PASS logo is where the headphone input jack is situated. Finally, the large volume control knob, which operates very smoothly, is surrounded by a large black ring. It is very impressive looking, indeed.

Around back, you’ll find the IEC input, two sets of RCA inputs, and one RCA preamplifier output.

[Editor’s note: the evaluation of the HPA-1 as a headphone amplifier was conducted by Ben Shyman in a separate audition, and he wrote all text pertaining to the headphone amp.]


The Hookup as a Preamplifier
I teamed the HPA-1 with a variety of amplifiers (Pass Labs XA60.8 mono blocks, Perla Audio mono blocks, Linear Tube Audio ZOTL-40, and Accuphase P-450), and my sources included the Line Magnetic DAC 1 and Fidelity-040 hybrid DACs, which received the digital signal from an MBL 1621 CD transport. The speakers I used during the review process were Tekton Design’s Double Impact towers, Lawrence Audio’s Cello and Double Bass, and Aurum Cantus’ V7F towers. The power cord used to run the HPA-1 was Archon’s power 1 level cord.

Performance as a Preamplifier
My first selection was Duke Ellington’s Masterpieces by Ellington (Columbia) to get a measure of how the HPA-1 would handle the spatial aspects of this big-band recording. It created a large soundstage with great depth and side-to-side dimensionality. Very much like a tube-based line-stage, the HPA-1 accurately portrayed the space between the players. Each individual player image had that “meat on the bone density” that you rarely get from a solid-state preamplifier.

My next selection was Wynton Marsalis’s The Magic Hour (Blue Note) to evaluate how the HPA-1 would render the warmth and fatness of Marsalis’s trumpet, along with the timbres/tonality of Dianne Reeves’s voice. If I did not know that the HPA-1 was transistor-based, I would’ve been fooled: the HPA-1 had the natural warmth and slight fullness that mimic tubes. Also, the music had an overall signature of liquidity and smoothness. None of this came at the expense of micro-details or nuances in the music. The HPA-1 was very transparent, offering the clarity that you’d associate with solid-state line-stages.

Feeling of Jazz - Wynton Marsalis Quartet | Ritrola

My next selection was the classic jazz album Mingus Ah Um (Columbia), by bassist Charles Mingus. It was very apparent that the HPA-1 could do justice to the deep and powerful sound of Mingus’s double acoustic bass when he would intensely pluck a string to get the most volume out of that note during his solo. What also came to my attention was the way that Danny Richmond played his cymbals with a beautiful tone that was reproduced with just the right amount of air and decay by the HPA-1.

Charles Mingus \ Mingus Ah Um, 1959 [Full Album]

My final selection was the brand new album by The Rolling Stones, Blue & Lonesome (Polydor). The Stones loved the playing of the great Chicago blues musicians, and their early music emulated their musical heroes. In that respect, this album is a return to form. Although I would not consider this CD to be well recorded, it does deliver the band’s raw power and emotion. The HPA-1 punched out this raw/gutsy music with great kick and vigor, regardless of which amplifier I used in the system. So, the HPA-1 can do pretty and sweet, yet it can also kick ass with great macro-dynamics and realistic grit when it has to.

The Downside as a Preamplifier
The three drawbacks I’m about to mention really nothing to do with the HPA-1’s superlative performance. First of all, there is no remote control. Second, the HPA-1 only accepts RCA/single-ended cables; you can’t use XLR/balanced cables. Lastly, there is no theater bypass option, so it really is not suited for a home theater rig, but only for a two-channel system.

Click over to Page Two to read about the HPA-1’s Performance as a headphone amplifier, as well as Comparison & Competition, and Conclusion.

Pass-Labs-HPA1-front.jpgThe Hookup as a Headphone Amplifier
To evaluate the HPA-1 as a headphone amplifier, I used headphones from Audeze (LCD-X, $1,699), Oppo (PM-1, $1,099), and Audio-Technica (ATH-W1000Z, $699). I used Wireworld RCA cables between a Mytek Brooklyn DAC and the HPA-1 amplifier, stock headphone cables from each pair of headphones, and the HPA-1’s stock power cable.

Performance as a Headphone Amplifier
I began with the album Friday Night in San Francisco (Phillips). Luckily this live performance at The Warfield Theatre by guitar virtuosos Al Di Meola, John McLaughlin, and Paco de Lucía was put to tape. Each musician is completely on top of his game. There are few live albums in which the intimacy between performers and crowd is so well developed and conveyed to the listener. Through the HPA-1, I could appreciate this intimacy at a near-religious level. In the song “Short Tales of the Black Forrest,” the audience demonstrates its high-level enthusiasm for McLaughlin and Di Meola when breaking into a blues jam, emerging from the Pink Panther theme song.

Short Tales Of The Black Forest - Al Di Meola & John McLaughlin

While the HPA-1 presents each guitar with pinpoint accuracy, clarity, and separation in all of Friday Night in San Francisco songs, this is especially true in “Fantasia Suite,” the only track where the musicians play as a trio. The HPA-1 also brought out other intangibles to elevate this one-of-a-kind performance to an elite level: the tapping, pick scraping, and communication between performers are easily heard and make it seem as if you were sitting in the front row on that Friday evening in 1981. In my view, headphone listening is about intimacy, and the HPA-1 is nearly perfect in this regard.

Moving to some late 1970s pop, I put on the second album from The Cars: Candy-O (Elektra, MQA, 24/192). The opening track, “Let’s Go,” is the album’s standout track and still gets played regularly on rock/pop radio stations. Throughout Candy-O, Benjamin Orr’s bass sounded deep and never muddy, and David Robinson’s drums had the punch and depth associated with the best floorstanding speakers I have heard, especially through the Audeze LCD-X headphones. Guitars had excellent tonality and decay. While the soundstage varied for each pair of headphones--with the Audeze being the widest and most spatial of the three--instrument separation and overall clarity were excellent through all three pairs.

The CARS - Let's go!(1979)

It was during my listening to Candy-O that one of the HPA-1’s most noteworthy characteristics began to emerge: no matter which pair of headphones I chose, the HPA-1 could coax maximum performance from them. The HPA-1 showed itself to be a versatile amplifier with any pair of headphones.

Blues legends Eric Clapton and B.B. King collaborated to record Riding with the King (Duck/Reprise, 24/88.2) in 2000, and the result was a double-platinum, Grammy-winning blues album. Through the HPA-1, Clapton and King’s acoustic version of Big Bill Broonzy’s familiar arrangement of “Key to the Highway” was elegant and highly refined. Acoustic guitars were balanced, and the overall presentation was airy and transparent, with pinpoint instrument placement in and across the soundstage. This included varying degrees of three-dimensionality, depending on which headphone I selected. In King’s upbeat and bluesy “Days of Old,” the balance between Clapton’s solo in the left channel and King’s comping and accompaniment in the right channel was so tasty that it expertly drew me in, almost like being in the studio with this duo of blues masters.

B.B. King & Eric Clapton - Key to the Highway

I concluded with Soundgarden’s Superunknown 20th Anniversary Edition (A&M Records). Superunknown routinely delivers a thick tapestry of sound; on tracks like “Limo Wreck” (guitar harmonics) and “Black Hole Sun” (Leslie speaker), the HPA-1 was always up to the task. Throughout Superunknown, bass was deep, authoritative, and highly punctuated. The bottom end never turned to mush, even with guitars tuned to low-D.

The most fun I had, however, was on “Spoonman,” the album’s best known and popular track despite its frequently changing time signatures, including the more unusual 7/4 time. In my view, the percussion track gives “Spoonman” its uniqueness. During the bridge, the spoons played by Artis the Spoonman (a California and Seattle street musician) were conveyed crisply and clearly. In addition, the sound of (seemingly) pots and pans, played by drummer Matt Cameron, adds to the song’s tapestry of sound. The spatial placement of each instrument was open and un-crowded, giving sense of space over the song’s distorted and punchy rhythm track. This was the case in all of the headphones I used.

Soundgarden - Spoonman

The Downside as a Headphone Amplifier
The HPA-1 has practically no sonic downside. It equals or outperforms almost all other headphone amplifiers I’ve heard. At $3,500, however, Pass Labs could include a level meter and remote. With every passing year, I think more about my overall health, and that includes my hearing--so I would especially appreciate having some confirmation of decibel level when sound emanates so closely to my ears. The omission of a remote control is simply a bummer. I enjoy relaxing on the couch and getting into a real listening groove, especially with headphones as comfortable as either the Oppo PM-1s or Audeze LCD-Xs. Having to get off the couch to adjust the volume as I switch between albums or songs on my iPad was a groove killer.

Comparison and Competition
As a preamplifier: I really could not come up with a solid-state preamplifier in the exact price range of the Pass Labs HPA-1 that would be competitive in its performance. Therefore, I’ll compare it with two much more expensive line-stages with which I’m very familiar. The Ayre Acoustics K-5XE, which retails for $4,350, has excellent transparency, good dynamics, and relatively far soundstaging abilities. However, it sounds like a typical solid-state device when it comes to timbres/tonality. It sounds somewhat “dry” and washed out in comparison with the HPA-1. The SimAudio Evolution 740P, which retails for $9,000, offers reference-level transparency, easy-to-hear micro-details, and excellent overall dynamics, but I found it to be analytical-sounding and somewhat sterile in its overall presentation. It does not offer the full image density or the overall liquidity, tonality, and colors of live music that I heard with the HPA-1.

As a headphone amplifier: The uber-high-end headphone amplifier market is a completely esoteric category where prices are high and unit sales are likely small. Despite this fact, the Pass Labs HPA-1 does have some noteworthy competitors. The King by Audeze retails for $3,995 and is a hybrid tube/Mosfet design. Woo Audo offers an extensive number of headphone amplifiers at prices that range from “comfortable for most mortals” up to $15,000. The WA5-LE is a tube-based design for $3,699. The SimAudio MOON Neo 430HA is a solid-state model that sells for $3,500. Finally, I would be remiss not to mention the HeadAmp Blue Hawaii for $5,000, the AURALiC Taurus MkII for $1,899, and the Cavalli Audio Liquid Lightening 2 for $4,499. There is no doubt that choices in the high-end headphone amplifier market, much like high-end headphones, are growing quickly.

The Pass Labs HPA-1 is the first headphone amplifier/preamplifier that this iconic company has ever produced. As a preamplifier, it outperforms solid-state preamplifiers that cost $5,000 to $10,000 more in its purity of timbres/tonality, its overall liquidity, its image palpability, the air it puts around individual images, and its tremendous soundstage depth and width. Does it exactly equal what great tube-based preamplifiers offer, as I stated at the beginning of this review? Not quite, but it’s very close indeed--to the point that I would want it in my system if I were going to use a solid-state line-stage. Like all Pass Labs gear, it is exceptionally well built, it’s very handsome in its appearance, and most importantly it performs like a champ across the board. If you can overlook the lack of a remote control and an XLR option, you’ll find that it kills in its performance and can compete with any line-stage on the market today, offering a bit of tube magic without the hassle and expense of buying and replacing tubes in the future.

As a headphone amplifier, the HPA-1 is unquestionably a five-star performer. It is hard to imagine a far better performer at any price. The HPA-1 is worthy of being mated with the finest cans available on the market today, such as the Focal Utopia ($3,999), the Audeze LCD-4 (3,995), or the STAX SR-009 ($3,799). But as our listening tests confirmed, the HPA-1 is such a high-quality performer that it coaxes maximum performance from whatever headphones with which you pair it. This is a testament to the HPA-1’s overall exceptional performance and versatility. It will draw you in closer to your music and provide a sense of intimacy that is nothing short of addictive and will keep you listening for hours on end.

Additional Resources
• Visit the Pass Labs website for more product information.
• Check out our Stereo Preamp and Headphones category pages to read similar reviews.
Pass Labs INT60 Integrated Amplifier at

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