I have to admit that I’ve been curious about this amplifier for a while now, and I’m happy to say that I managed to get my hands on it with the help of the guys from Jack-Fi.ro.
While I have managed to listen to some absolutely massive speaker amplifiers from Pass in the past, this is the first time I’ve had one at home. Yes, this time it’s a headphone amplifier, not a speaker amp, but I believe it retains the sound characteristics that I’m going to describe below.
You can find more details directly on their website. I will add a few directly here.
The HPA-1 headphone amplifier was designed ground-up to become what we believe is one of the very best sounding headphone amplifiers available today. With low feedback, wide bandwidth and a direct coupled MOSFET output stage, this musical instrument drives even the most difficult headphone loads with ease, power and grace. The HPA-1 also functions as a line-level preamplifier that sonically rivals much higher-priced competition. The measured performance is superb and the sound even better.
| Gain (dB) | 8 db |
| Frequency Response 10hz – 100k | -1 dB |
| Output Power into 20 ohms | 3500 mW |
| THD + Noise | < 0.005 at 1V out |
| Out Power into 300 ohms | 200 mW |
| Input Impedance | 50K Ohm |
| Output Impedance | < 2 ohms |
| Power Consumption (Watts) | 23 |
| Unit Dimension (W x D x H) (In.) | 11 x 13.5 x 4 |
| Unit Weight (LBS) | 14 |
Pass Labs’ HPA-1 is capable of delivering full-range dynamics across the entire frequency range, even when driving headphones that present difficult loads in terms of impedance or power consumption or both.
https://www.passlabs.com/wp-content/uploads/2020/12/HPA-1_om.pdf
Pass Labs’ designers knew that in order to stand out from the crowd, and satisfy their demanding customer base, the HPA-1 had to establish higher standards for audio performance. That has been accomplished first, by the conceptual approach of designing the HPA-1 as a real Class-A power amplifier, and not as an accessory offering only incremental performance gains. Second, by cutting no corners in circuit design, while omitting unnecessary frills. Thirdly, by sparing no necessary expense in execution.
The foundation of the HPA-1’s engineering is a custom, low-noise shielded toroidal power transformer with a Faraday shield between windings as well as a mu-metal shield around the circumference, feeding a discreet low noise regulated power supply for the audio circuits. The importance of the power supply is often overlooked and plays a large part in overall performance of the amplifier. The HPA-1’s amplifier circuits are low-feedback, wide-bandwidth discreet designs employing a J-Fet input stage and a Mosfet output stage biased into Class A-biased direct-coupled output stage.
The HPA-1 easily drives headphones presenting loads from 15 to 600 Ohms, particularly excelling on planar headphone designs. The sound is rich and detailed.
It’s been a while since I’ve had a full Class A headphone amp. The introduction above sounds impressive, so we just need to put it to the test and see how this baby sounds. I’m excited.
Listen Impressions and tests
Check out the video review here:
So, first of all, this is a single-ended amplifier, so I had to dust off my AudioQuest Sky interconnects and match it up with my Rockna Wavelight DAC.
Most of the tests were done with the Meze Elite & Hifiman HE1000SE.
PC (Matrix USB Card -> AudioQuest Diamond USB cable -> Denafrips Gaia -> basic i2s cable -> Rockna Wavelight -> AudioQuest Sky RCA interconnects -> Passlabs HPA-1 -> Silver Norne cable > Elite | Silver Lavricables for Hifiman HE-1000Se). I also used the hybrid Noir headphones from Forza for both headphones.
I would have liked this amplifier to be fully balanced, and I was a bit afraid that I wouldn’t get the best out of the DAC. Of course, I don’t know how it would have sounded from the balanced output, but I didn’t feel like I was missing something. I was actually immersed in the musical experience, which I’ll describe below. While I would have liked the amp to be balanced, I wish for this only for wider compatibility/connectivity purposes. As for the sound quality, I just can’t complain. Also, the pre-amp feature comes in handy, but I would have preferred a remote, so I can easily use it while I listen to my speaker system.
Before that, as you can see above, Pass states that it can easily drive headphones from 15 to 600 ohms. I thought…ok… challenge accepted. I have a pair of Beyer Dynamics DT880 600 ohms. These headphones are reportedly hard to drive, and the best amplifier I’ve heard so far with them was the Ferrum OOR.
I was surprised to see that I was at 55% volume, and I already had a good volume and, most importantly, good dynamics. So yes, the HPA-1 does what it says, and it does so brilliantly.
This unit had no burn-in, so I had to let it sing. I think I’ve surpassed 150 hours in total. While it sounded quite impressive from the start, the sound indeed changed over time: it opened up, the soundstage got deeper, more holographic, the musical notes more rounded, the depth of the bass improved significantly, and the dynamics gained more energy.
Bare in mind that if you want to get the best out of it, it needs a little bit of warmup before it gets to full potential.
But let’s delve into the depth of the musical experience.
Four Wild Horses – David Munyon
The vocals immediately grabbed my attention. The lead singer’s voice is incredibly deep, well-textured, and natural. When the backing vocals entered the scene, I was immediately immersed in the musical experience, as the depth of the soundstage and the holography created were mesmerizing. The vocals have a good pluck/sparkle, but are also well-rounded with good extension. I’m not sure what the instrument that appears after the middle of the song is, something like a pipe, but when it emerged in the song, the texture, weight, and natural detail gave me goosebumps once more.
A pirate’s life – Bryan Tyler – Assassin’s Creed
The song showcases the vibration of strings and percussion instruments, the depth of the bass, and textural capabilities right from the first second. I was just floored by the experience. I had to close my eyes, as I was instantly transported into the song, riding the chords, vibrating with each instrument, becoming one with the song. I felt the plucks and percussion, the body of the instruments, as though each displaced air in a way that created a powerful vacuum effect and the reverse, pushing and pulling me in both directions. This was accomplished while everything sounded incredibly natural, with incredibly detailed textures.
The Man Comes Around – Johnny Cash
Oh man. It seems that every song is an unforgettable experience so far. You know when you have so many choices of good food in front of you and you just don’t know which to focus on first? (Yes, I am a foodie). This was the same. I didn’t know what to love more, the guitars or the voice. Man, the guitars were so energetic, but also well-rounded (in a good way), as each pluck had a complete decay (fast, well controlled), that gives you a sense of the whole body of the instrument. The voice had a very addictive presence, with excellent textures and detail.
Earth Melodies – Ekaterina Shelehova
Man, I feel like I need a degree in literature to be able to describe this experience properly. I feel as though I don’t have the words to properly express the emotion, joy, and experiences with this song. I will give it a try, though. First of all, this song brought me to tears of joy and emotion. It was like a literal rollercoaster. I was riding the voice, feeling all the inflections as if I were on a rollercoaster – up, down, middle. I felt the voice traverse multiple layers of the space-time continuum, transcending 3D space. I traveled back in time, then further into the future, visited Narnia, Middle Earth, and at one point, I think I met Odin when he was creating the realms. It took me a while to get back home after this song. I was older, had gained knowledge about the meaning of life, and was a bit tired after this intense journey.
Oh man, the experience with this song was so fun as well. After being a bit emotionally spent from the previous song, this one was an infusion of energy. Every instrument vibrated with life, and the bass was absolutely stunning. The impact is strong, it goes deeeeeep, and it has very good control. It’s as if it creates a vacuum in both directions, and you’re just a ragdoll being tossed around. I felt the bass in my body, not in my ears. It’s a strange yet lovely sensation.
I felt the air of the saxophone. It was so well-textured, so natural, and so present that it gave me the impression I was the one blowing into it. You feel it in your throat. Also, the layering and holography of the scene were stunning.
Apparently, you just can’t listen to music casually with the HPA-1. I was immediately transported into the song, not just the stage. It was better than being on the stage. I jumped from cello to cello, vibrating with each chord. I was thrown from note to note, from vibration to vibration. I felt the song in my body. When the drum effect kicked in, I was swept deep into the vibration of life energy and it took me a while to return to my “corporeal” form.
Summary
Bass
The bass didn’t come to play, it came to slay. Think of a wild beast awakening from hibernation, that’s the bass after the burn-in. It’s like a playful giant, pushing you, pulling you in, then chucking you around just for kicks. With a punch that would make Muhammad Ali think twice, impeccable control, and the ability to dive deeper than James Cameron’s submersible, the bass brings texture to life.
Midrange
Prepare to sign your life over to the midrange, because it is to die for. If Mother Nature herself was singing, this is what it would sound like: textured, natural, a song of life and energy. Every instrument, every voice, comes alive in a chorus of pure sonic perfection. Prepare to be stunned.
Treble
Oh, the treble. Think of a champion figure skater, poised, precise, and never a foot wrong. It’s got the sparkle, the detail, without any hint of harshness. It integrates like a perfect cocktail, blending seamlessly with the rest of the sound to create an auditory feast that’s as natural as it gets.
Tonality
If music had a taste, the tonality of this amplifier would be gourmet. It’s a Michelin-star serving of natural, musical delight, with no note out of place or overpowering the dish. You’re not just listening, you’re dining with your favorite artists, each one contributing to the incredible sonic banquet.
Soundstage/Imaging
Step into the IMAX of soundstages. I’ve encountered solid-state amps before, but nothing like this. This is like stepping into the Star Trek Holodeck, so layered, so 3D, so deep you might need a submarine. Navigate the musical landscape, pinpointing every instrument in the orchestra, each one holding its own even in the most crowded scene. I had to double-check there wasn’t a speaker lurking behind me. If you’re seeking an immersive musical journey, strap in, because this is the ride of a lifetime.
Transients, Energy, Dynamics
These are the secret spices in this amplifier’s recipe. It’s not just playing the song; it’s bringing it to life, breathing energy into every instrument, every vocal note. But here’s the kicker: this isn’t raw power; it’s refined, a delicate balance of tactile energy and natural presence. The notes leap into existence, fully formed, full of detail, and quick as a hummingbird’s wings, never lingering longer than they should. This isn’t easy to pull off; many have tried, few have succeeded, but HPA-1? It nails it.
Textures & Details
Textures & Details I think these should go hand in hand here. Have you played around with adding 4K textures to recent games? They are an important part of the detail and the overall perception of the sound. You have seen me talk about textures above, but not too much about detail. Why? Because, this amp is above talking about detail itself. The textures are so real, you could touch them, and the details are woven into the fabric of the sound, creating a mesmerizing, lifelike experience that will leave you spellbound.
Conclusion
You might be reading these descriptions, raising an eyebrow, and thinking, “Has this guy been partying with unicorns on cloud nine?” Let me assure you, no unicorns were involved, nor any imbibing or inhaling of questionable substances. This amplifier simply catapulted my listening experience into the stratosphere. It was emotional, it was magical, and it left me feeling like I had just run a mental marathon – an exhilarating race through a realm of fascinating rhythms and riffs.
Why the workout, you ask? Well, with this setup, ‘casual listening’ just isn’t in the vocabulary. It’s like telling a tornado to chill or asking a rocket to take a leisurely stroll upwards. Every time I used it, I found myself stopping mid-task, utterly consumed by the symphony unfolding in my ears. Each track stirred up intense emotions within me.
This bad boy is the heavyweight champion in my roster of tested headphone amplifiers. It’s the kind of match for the Meze Elite that makes you hear wedding bells in the distance.
Now, do I recommend it? Well, let me put it this way: Are you yearning for a sonic journey that blurs the line between you and the music? Do you want to feel each pulsating note and resonating voice echo within the very marrow of your bones? Do you want your music to not just speak, but shout its passion into the vast auditorium of your soul? If your answer is a resonating ‘YES’, then my friend, you are one amplifier-testing session away from a life-changing eargasm. And remember – don’t just take my word for it, and let your ears be the judge!
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