HPA-1c

Reviewer: Srajan Ebaen
Financial interests: click here
Main system: Sources: Retina 5K 27" iMac (i5, 256GB SSD, 40GB RAM, Sonoma 14), 4TB external SSD with Thunderbolt 3, Audirvana Studio, Qobuz Sublime, Singxer SU-6 USB bridge, LHY Audio SW-8 & SW-6 switch, Sonnet Pasithea, COS Engineering D1, Laiv Audio Harmony; Active filter: Lifesaver Audio Gradient Box 2; Power amplifiers: Kinki Studio EX-B7 monos & Gold Note monos on subwoofer; Headamp: Enleum AMP-23R; Phones: Raal 1995 Immanis; Loudspeakers: Qualio IQ [on loan] Cables: Exact Express Flame, Furutech; Power delivery: 2 x Kinki/Vinshine Tai Hang on amps and source stack, Furutech DPS-4.1 between wall and conditioners; Equipment rack: Artesanía Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc amp stands; Sundry accessories: Acoustic System resonators, AudioQuest FogLifters; Room: 6 x 8m with open door behind listening seat; Room treatment: 2 x PSI Audio AVAA C214 active bass traps
2nd system: Source: FiiO R7 into Soundaware D300Ref SD transport to Cen.Grand DSDAC 1.0 Deluxe with POW; Preamp/filter: Lifesaver Audio Gradient Box 2; Amplifier: Kinki Studio EX-M7; Loudspeakers: ModalAkustik MusikBoxx + Dynaudio S18 sub; Cable loom: Exact Express Earth; Power delivery: Vibex Granada/Alhambra, Akiko Audio Corelli Corundum & Castello Solo; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Furutech cable lifts, Furutech NFC Clear Lines; Room: ~3.5 x 8m
2nd headfi system: DAC: Cen.Grand DSDAC 1.0 Deluxe with POW; Headamp: Cen.Grand Silver Fox; Headphones: Raal 1995 Magna, HifiMan Susvara
Desktop system: Source: HP Z2 work station Win11/64; USB bridge: Singxer SU-2; DAC/headamp: iFi iDSD Pro Signature; Amps: Topping B200; Speakers: Virtual Hifi Viper; Headphones: Final D-8000, aune SR7000
Upstairs headfi system: FiiO R7; Headphones: Meze 109 Pro, Fiio FT3
2-channel video system: Source: Oppo BDP-105; All-in-One: Gold Note IS-1000 Deluxe; Loudspeakers: Zu Soul VI; Subwoofer: Zu Submission; Power delivery: Furutech eTP-8, Room: ~6x4m
Review component retail: $4'045

When 'c' is a superb grade. It's the new iteration of the HPA-1 from California's Pass Labs. The letters abbreviate Head.Phone.Amp. The 'c' suffix—my name is Coburn, Wayne Coburn—signifies a brand-new power supply with revised grounding for superior S/NR and sonics.

"We always retain plenty of parts for repairs and for our standards started to run low on a key production part. That component of the amp's original power supply had become unobtainium. It's always fun when that happens. To prevent future shortages, our resident low-level signal wizard Wayne Coburn who does all our preamps looked into alternatives. While at it, he took it upon himself to revisit the entire PSU. In the process he redesigned it completely. These improvements warranted the model's new 'c' designation."

A parts shortage as the mother of invention. That was the brand's resident Irishman Desmond Harrington grading for me the model's most recently earned 'c'. It makes 'a' and 'b' yesteryear's generations.

I always thought a 'c' grade far more cool and contemporary than those brainy know-it-all A-listers. Being in bad need of some cool myself right about then, I threw my name in the hat. Teacher's pest and all that; from the farthest row in the classroom. When even your worst student asks for extra homework, you just know you're onto something.

"Power supply is 80%." It's how the cool dragstrip lads explain that something. They should know. They always smell of burnt rubber, gasoline and testosterone.

Gentlemen, rev up your engines?

Now the racetrack connection wipes out spectacularly. As Wayne put it, "the noise floor is 10dB lower, distortion lower, power unchanged." Going faster is any grease monkey's mantra. Bigger engine. More torque. Steeper acceleration. Superior aerodynamics. What's a racer's equivalent for less distortion and lower noise without extra power? Less moving mass? By not altering its class A direct-coupled Mosfet gain circuit of 23-watt power consumption, the HPA-1c still delivers 3.5wpc into 20Ω with 2Ω Z-out. That nets 2 watts into 32Ω. If today's market has cans of grander appetites—the Tungsten perhaps—bangers might wish to check ultimate loudness potential on their system's voltage gain? To be sure, this circuit adds up to 8dB to our source signal. With two single-ended inputs, the HPA-1c can't tap double-voltage XLR outputs but its own switched line-out doubles as minimalist preamplifier. Finish options are Ford Black and Chevy Silver. Real racers of course would quickly decry our hobby. Where today's ultra-speed cameras clearly mark who crossed a track's finish line first should things get too close for the naked eye, what sounds best in audio is vague and contentious. How to ace a hifi race becomes a real mystery when the observing audience can't agree on anything, much less who won. It's why motorsports don't make a good tie-in. But that hasn't prevented Alvin Lloyd from running Grand Prix Audio as a winning recipe; or hifi reviewers from invoking car examples to make a point. At least that's my excuse for doing it. What's yours for still not listening to headphones?

I reviewed and awarded the original HPA-1 in November 2016 [above] to not remember specifics. Nine years ago I lived in our first Irish house not the present third. My system was quite different as is my current headphone harem. What I do remember is just how excellent this machine was as a traditional linestage. Lack of remote control certainly rendered that utility bareboned by modcon standards but the sound made up for it. The HPA-1c thus promised to be an even better preamplifier for simpler rigs which don't have more than two single-ended sources and can do with manual labour – er, volume. A button push on the front panel toggles between headphone and speaker modes. What could be easier?

Letting regular contributor Dawid Grzyb start only leaves me with a "what he said" sentence to pen. Easy. Seriously though, two opinions are always useful. Over the years my own systems have slimmed down to go source direct. Hence no more preamps. Dawid runs either Trilogy's 915R preamp with 6H6P 'super' tubes; or a Thöress DFP pre/head-amp where one 6J5GT per channel drives a triode-strapped 12GN7 unity-gain buffer. He was ideally placed to suss out the HPA-1c's preamplitude chops. My place goes heavier on HeadFi than his. I could compare aune's and Soundaware's class A decks and class AB contenders by way of Kinki's THR-1, Cen.Grand's Silver Fox and Enleum's AMP-23R. The latter is also present in Dawid's system. So our travelling HPA-1c sample would meet plenty of contrast agents. How much separates it from the original other than measurements? That's for those to say who can compare both, not us. Ditto ultra-efficient in-ear monitors. IEM might just be the type load most appreciative of a still lower noise floor than that of original HPA-1 which I had zero issues with on my loads. If over-ear headphones of standard efficiency would show less or no difference over the original, revisiting a design that already withstood the test of time for nine years would still be an excellent exercise to track ongoing relevance.