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 HomeTheaterReview.com, 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.
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.
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.