Nearly a decade after the release of the original HPA-1, the Pass Labs HPA-1c arrives as its successor, refining the proven formula with thoughtful and meaningful improvements. That’s our subject this time around—enjoy!

Linestage-fi

When the original HPA-1 appeared, it represented Pass Labs’ first deliberate step into the headphone world, applying the company’s analog know-how to a smaller, more personal format. It was simple, discrete, and pure Class A—an amplifier built with the same philosophy as the brand’s larger stereo gear. That model went on to earn a reputation for its transparency, reliability, and restraint in an era when many head-fi designs leaned on broad skill set rather than their fundamental utility. The new HPA-1c was born not out of marketing ambition but necessity. Several key parts in the original power supply became unavailable, forcing Pass Labs to either discontinue production or redesign the circuit. Rather than let a proven design fade, the company’s low-signal guru Wayne Colburn revisited his earlier work with the intent to modernize it without altering its soul. What began as a practical revision evolved into a deeper refinement of how the amplifier managed power, grounding, and noise.Colburn’s re-engineering led to a new supply architecture with new voltage rails, improved voltage regulation, and redesigned grounding routes. These changes collectively yielded a roughly 10dB lower noise floor and a more stable operating envelope—meaning the HPA-1c runs cleaner and quieter than its predecessor while maintaining identical gain and drive characteristics. Beyond these internal refinements, the amplifier’s purpose remains the same: a dedicated analog headphone amp that doubles as a compact preamp for purist two-channel systems.

Seen from a broader view, the HPA-1c embodies the Pass Labs ethos at its most distilled. It is an update that respects the past while ensuring longevity in the present, the result of careful engineering decisions made for the right reasons. In revisiting the design, the team didn’t chase novelty—they safeguarded a modern classic, making sure it could continue serving enthusiasts for another decade to come. The story of the HPA-1c, then, is less about change and more about preservation. It exists because Pass Labs chose to adapt thoughtfully rather than move on. So while the “c” might officially stand for its new current-grade supply, it could just as easily symbolize continuity — a continuation of Pass Labs’ unwavering belief in minimalist analog design. It might also nod to Colburn’s hand in its creation. As usual with Pass Labs and FirstWatt projects, I received the HPA-1c loaner first; it will then make its way to Srajan, who has already begun weaving together our combined impressions.In its roster, the Pass Labs HPA-1c stands as the only full-fledged headphone amplifier. Measuring 28 × 11.5 × 33cm (W × H × D) and weighing 6.35kg, it’s rather hefty and runs hot. Its discrete Class A circuitry demands proper heat dissipation, hence the tank-like enclosure built from thick aluminum plates. This is a wide-bandwidth design, with a frequency response extending from 10 Hz to 100 kHz — an uncommon specification. Output power reaches 3.5W into 20Ω and 200mW into 300Ω, with THD+N below 0.005% (at 1V). Input impedance is 50kΩ, output impedance sits below 2Ω, gain is rated at 8dB, and power consumption totals 23W. Silver and black are the available color options.

Visually, the HPA-1 is identical as its predecessor, so quite the brutalist. Transistor-based head-fi gear rarely takes on such a substantial, imposing form. The enclosure itself is all business — robust, industrial, and purposeful rather than decorative. The thick front plate’s beveled edges, exposed hex screws, and solid anodized panels convey the kind of honesty and integrity that define Pass Labs design. It looks unapologetically functional yet, in its own way, quietly elegant. Every panel fits seamlessly with the next, creating a reassuring sense of precision and permanence. Build quality this solid and attention to detail this exacting are rare. While making a visually modest, even plain, product feel desirable isn’t easy, the HPA-1c manages it effortlessly.The front panel leaves no doubt about its lineage. The large, silky-smooth aluminum volume knob set within a thick black surround is unmistakably Pass Labs. The model name sits neatly in the lower-left corner, while a shallow curved recess runs across the front, housing three satisfyingly clicky buttons with blue LEDs for Input 1, Input 2, and Preamp. A small LED above the first button indicates power status. To the right sits a single 6.3mm locking Neutrik headphone socket — and that’s it. The HPA-1c gets away with this minimalist approach, omitting XLR or 3.5mm outputs and anything superfluous. A CNC-milled Pass logo above the headphone jack and the nearby volume wheel complete the restrained aesthetic. By modern standards, the layout is austere, and the rear panel follows the same philosophy: a fused IEC power inlet with a main on/off rocker, one RCA preamp output, two RCA inputs and nothing more than that. The amp rests on four aluminum feet with rubber washers.

The HPA-1c is purely analog — no DAC, no display, no remote, and not even a digitally controlled relay volume system. It was built for one purpose: to deliver the best possible analog performance within its design limits and price. As the most affordable product in Pass Labs’ lineup, it represents a deliberate balance between cost, craftsmanship, and sonic integrity. While most buyers will approach it as a head-fi amplifier first and foremost, it also promises superb preamp performance, just like its predecessor did. That secondary function isn’t a gimmick; it was a core design goal from the outset. In essence, this is two high-caliber components housed in one chassis — a genuine two-for-one execution done the Pass way. Operation is straightforward: flip the rear power switch, and the amp enters a brief mute state indicated by a flashing LED. After 20 seconds, it becomes fully active — a sequence managed by a custom microcontroller. Designed for continuous operation, the HPA-1c is always ready to perform. Selecting between the two inputs is done via the front buttons, while engaging the “Preamp” mode instantly disconnects the headphone output.Inside, the HPA-1c is a single-ended, fully discrete, no-feedback design that closely follows the architecture of the original HPA-1. The only op-amp present is a DC servo. The power supply — regarded as contributing roughly 80% of the amplifier’s sonic character — is a serious affair. An unusually tall, low-noise Avel Lindberg toroidal transformer with dual Faraday shielding feeds four capacitors totaling 40,000 µF, followed by discrete voltage regulators, each with its own heatsink. The updated power supply in the HPA-1c now provides ±15V rails instead of the earlier 24V equivalents. The amplification stage employs Toshiba JFETs for voltage gain and Fairchild MOSFETs for the directly coupled Class A output stage. An Alps potentiometer controls volume, while all signal and power-supply circuitry are mounted on a single large PCB with redesigned grounding routes. Now, onto the sonics.

The plan for testing the Pass Labs HPA-1c loaner had taken shape long before it even arrived. Since I don’t do much head-fi these days, it made more sense to first use the unit as a preamp within my speaker setup. To make the necessary component swaps easier, I adjusted a few things. The Innuos server/streamer, LampizatOr DAC, and sound|kaos monitors remained in place. However, Trilogy’s 995R/915R analog combo was replaced by the Enleum AMP-23R, used purely as a power amp and driven alternately by the Pass or the considerably pricier Thöress DFP. Once that comparison was done and dusted, the newcomer Pass and the AMP-23R went head-to-head as head-fi decks. To chart their performance, I used the Susvara Unveiled and Campfire Cascade headphones. Finally, the Pass was also paired with Vision Ears VE5 IEMs—partly to gauge its noise floor, and partly because any such in-ear experiments aren’t on Srajan’s menu.Let’s first talk about the Pass Labs house sound. Every product from this company that I encountered before the HPA-1c shared a similar sonic DNA. If I had to distill that character into a single word, elegance fits best. By that I mean a voicing that doesn’t elevate any single trait above the rest. Instead, it combines tonal richness and fruitiness with resolution and openness, albeit without a clear bias toward either illumination and spatial grandeur or weight and bass authority. To my ears, the Pass Labs voicing sits roughly midway between these trait groups, leaning slightly toward the latter. It ultimately also draws from both and blends them in quite balanced proportions. I consider this carefully crafted approach highly universal—typical of well-designed class A circuits—and inherently safe. Pass Labs gear performs brilliantly in well-sorted setups where no drastic tonal corrections are needed to restore balance. The HPA-1c continues that lineage: its mission isn’t to fix a system that sounds off, but to elevate one that’s already right. Yet it’s also the second Pass component I’ve encountered whose sonic identity is anchored by one dominant trait that forms the foundation for everything else. I’d already sensed this particular quality in the XP-22. The HPA-1c also embeds it without a miss.

When a manufacturer highlights a low SNR, I immediately think of strong noise rejection expressed through a particular kind of audible silence. That may sound counterintuitive, but stay with me. The more noise is stripped away, the darker the virtual backdrop behind all sound sources becomes. As that residual haze disappears, this background turns into true blackness—the kind that separates good gear from top-tier performers. This isn’t a new discovery; many audio specialists known for cables and isolation products already pursue that same goal. My entire setup is filled with accessories designed to suppress incoming noise so I can fully experience that eerie, ink-black canvas and all the benefits it brings. Just as the Pass Labs XP-22 before it, the HPA-1c also granted me access to that realm within seconds of the first listen, as if it wanted to make perfectly clear that this seductive darkness was its designers’ top priority.Although the HPA-1c’s ability to render a pristine, inky-black space might seem like just one attribute, the impact of this backdrop is far-reaching. First, it keeps a host of unwanted artifacts at bay. This is precisely why the HPA-1c simply doesn’t know how to sound sharp, piercing, garish, or overly exposed. Its aesthetic in fact lies squarely on the opposite side of that spectrum. Secondly, its sound is utterly free of grain, remarkably smooth, non-fatiguing, flowing, and genuinely refined. Thirdly, that high degree of noise rejection serves as the enabler for muscular density, a wide tonal palette, vivid color saturation, expansive dynamics, agility, and control. On gentle vocal or instrumental recordings, it sounds sweet, saturated, voluptuous, and serene, yet it easily reveals its firm, contoured, open, and hard-hitting nature on heavy rock, metal, or bass-rich ambient tracks. Its charmingly organic, tonally rich personality always shines through—but how much of it surfaces depends on the music at hand, shifting the listener’s perception accordingly. Most importantly, the HPA-1c makes it abundantly clear that audible flashiness—manifested as roughly chiseled edges or excessive brightness—is simply not part of the manufacturer’s sonic vocabulary. As elegant and posh as this aesthetic is, it steadfastly avoids the sort of tricks that, over time, lead to fatigue. This is precisely why Pass Labs hardware, including today’s HPA-1c, can outlast many speakers, DACs and amps—and why this safety is one of its core assets.

Meanwhile, the Thöress DFP is a very different, highly specialized beast. Its vintage exterior and use of a 6J5GT driver tube for a 12GN7 unity-gain buffer might suggest a sound built primarily on warmth, harmonic richness, and that pleasing sense of body and weight. While that impression isn’t entirely wrong—and the DFP certainly embodies some of those traits—it also has three surprising aces up its sleeve: enormous dynamic range, remarkable speed, and a striking sense of spatial intimacy that makes nearby sound sources feel large, utmost present, and alive. These qualities define the DFP’s unique character, making it an unusually direct and engaging preamp. Although I don’t use it often, this is the very reason why I’ll never part with it. On a more personal and perhaps idealistic note, to me the DFP represents the very best this hobby can offer. That it so clearly reflects its maker’s values and engineering skills is no small part of its charm.Before moving forward, let me emphasize that the HPA-1c’s character—as outlined above—remained distinctly pronounced regardless of context. The showdown between this machine and the DFP proved both fascinating and entertaining, but first things first. When switching between them, I never sensed the threefold price gap that separates the two. That initial impression alone confirmed that today’s Pass felt perfectly at home among far more expensive components, and at no point did I consider it the weak link in my finely tuned system. That was no surprise, as even the most affordable gear from Nelson & Co. delivers consistently high—and yes, safe—performance that keeps the upgrade itch at bay. Yet while both preamps impressed, the DFP and HPA-1c were audibly different in character. With the former in play, the presentation became more incisive, articulate, and outlined—quicker on its feet and more immediate, which is rather ironic given its tube pedigree. My system with the DFP in it felt snappier and more electric, whereas the HPA-1c leaned calmer and sensibly darker. The former’s sportier attitude suited my taste perfectly, though it sometimes rendered certain recordings a bit mechanical, with a touch of grain here and there—as if that was the price for the extra energy. In that sense, the DFP consistently produced a more juvenile and intense sound that wanted my full attention.

In comparison to the DFP, the HPA-1c sounded effortlessly fluid and organic throughout my playlist, unfazed by whether rock, metal, or orchestral works were on the menu. The Pass simply had its priorities arranged differently from its rival. “Darkness” is often a polite euphemism for limited resolution, intelligibility, or dynamic range—but not in this case. The HPA-1c’s inherent blackness and firmly grounded tonality, courtesy of its remarkably low noise floor, yielded a presentation that was exceptionally informative, dynamically expansive, coherent, and always ready to entertain. If the DFP projected its brilliance outward, the Pass glowed from within. Where the former was radiant and extroverted, the latter felt sensual, grounded, and quietly confident—yet capable of surprising muscle, agility, and speed when called upon. If the Thöress were a DAC, it would be a modern ΔΣ design with DHTs in its output stage, while the Pass would be a contemporary R2R counterpart. All told, the HPA-1c left me thoroughly impressed as a preamp—a remarkable feat for a device conceived primarily as a headphone amplifier.Against the AMP-23R, the HPA-1c—used as a headphone amp—communicated its core virtues even more convincingly than it did against the DFP. That didn’t come as a surprise, given the Enleum’s inherently quicksilver, highly informative, elastic, and radiant nature—essentially a profile that sits on the opposite end of the spectrum. With the Susvara Unveiled up front, the Enleum delivered feistier, tighter, and more authoritative bass, paired with a somewhat leaner midrange, more specific vocal and instrumental outlines, and a shinier, slightly more extended top end. Although these headphones aren’t quite as demanding a load as their predecessor, the HPA-1c’s volume knob still had to reach about 80% to achieve satisfying SPL. Once there, I was genuinely impressed. The Pass didn’t hit quite as hard in the low end as the Enleum—but to expect that would be unfair. The Susvara Unveiled may crave less power than the original Susvara, yet they still appreciate it in generous supply. While most listeners would have agreed that the Enleum was a better companion for these cans, the Pass brilliantly showed their tonally packed, remarkably informative, enjoyably liquid, spatially sorted and complex profile. The pairing sounded in a way that invited very long listening sessions without any signs of listener fatigue. Considering this, the HPA-1c neither felt threatened by the AMP-23R’s extreme resolution, nor by its off-charts dynamic potency. Instead, it did its own thing to a very high standard.

As inefficient as they are, the Susvara Unveiled cans were better suited to the Enleum than to the Pass. It was time to correct that leverage and bring in an easier load — the Campfire Audio Cascade. With their 100dB efficiency, the Pass finally had its moment of sweet revenge. The Cascades’ V-shaped tuning emphasizes both ends of the spectrum: bold, slightly bloomy bass and crisp highs, with a recessed midrange in between. Driven by the Enleum, they sounded spicier, twitchier, more radiant, and speedier — but also stiffer and less saturated in tone. The Pass, by contrast, delivered its trademark organic warmth, full-bodied tone, delicately rendered detail, and an inviting, atmospheric presentation. Most importantly, with the Campfires, both the HPA-1c and the Enleum proved equally fast and supple, rendering the Enleum’s earlier advantages irrelevant. Ultimately, the Pass struck me as the more synergistic match, and I imagine most listeners would find this pairing more balanced and better suited for long, relaxed listening time. It was also worth noting that, with the Campfires engaged, the Pass ran quieter than its rival in terms of background noise. To explore this further, I paired it with the 5-driver VE5 IEMs, which boast 122dB efficiency. Although using such sensitive in-ears with a desktop amp was neither practical nor common, I wanted to hear how much hiss the VE5s would reveal with the Pass — they didn’t. At least, my ears couldn’t detect any residual shimmer, only enveloping blackness. For a desktop amp, this was a remarkable feat and a true testament to its vanishingly low noise floor. Lastly, the VE5s were designed for outdoor use with battery-powered gear — DAPs and DAC/amp combos — many of which proved far noisier with these IEMs than the Pass. Go figure.

Eight years ago, I praised the Pass Labs HPA-1 as one of the finest headphone amplifiers I had encountered at the time — and an exceptional preamp to boot. In fact, had I been looking for the latter utility for my desktop system back then, I would have seriously considered the Pass for that role alone. Fast forward to today: my hardware, taste, and reviewer experience have evolved, yet the new Pass Labs HPA-1c impressed me every bit as much as its predecessor did in 2017. Yes, it remains a minimalist single-ended design without a remote control, but to me that hardly matters given what it delivers in return. Artfully voiced, built like a tank, and sensibly priced for its pedigree, the Pass Labs HPA-1c stands as a must-audition for anyone seeking an exceptional and thoroughly dependable preamp and head-fi companion — one that reminds us exactly why we fell in love with this wonderfully eccentric audio hobby in the first place.

Associated Equipment:

• Amplifier: Trilogy 995R, FirstWatt F7, Enleum AMP-23R
• DAC: LampizatOr Horizon360 (Stradi 5U4G + Psvane Summit 4x KT88 / 2x 6SN7)
• Speakers: Boenicke Audio W11 SE+, sound|kaos Vox 3afw
• Transport: Innuos Statement, fidata HFAS1-S10U
• Preamplifier: Trilogy 915R, Thöress DFP
• Speaker cables: Boenicke Audio S3, LessLoss C-MARC
• Headphones: HifiMan Susvara Unveiled, Campfire Audio Cascade, Vision Ears VE5
• Speaker signal conditioning: LessLoss Firewall for Loudspeakers, Boenicke ComDev
• Anti-vibration conditioning: 6x Carbide Base Diamond (under streamer), 6x Carbide Base Micro Diamond with TwinDamp inserts and spikes (under DAC and pre), Vibra 68 (under speakers), 12x LessLoss Giant Steps (under streamer, DAC and pre)
• **Interconnects: **LessLoss Entropic Process C-MARC, Boenicke Audio IC3 CG
• Power components: Gigawatt PC-3 SE EVO+/LC-3 EVO, LessLoss C-MARC, LessLoss Entropic C-MARC, LessLoss Stellar C-MARC, LessLoss Power Distributor into Boenicke Audio Power Gate, ISOL-8 Prometheus
• USB components: AudioPhonique Desire USB
• Rack: Franc Audio Accesories Wood Block Rack 1+3
• Network: Fidelizer EtherStream, Linksys WRT160N
• **Music: **NativeDSD

Retail prices of reviewed components in EU (incl. VAT):

• **Pass LAbs HPA-1c: **$4’045

Manufacturer: Pass Labs