Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 12.2), PureMusic 3.02, Qobuz Hifi, Tidal Hifi, Fore Audio DAISY1, COS Engineering D1, Aqua Hifi La Scala MkII, AURALiC Vega, Aqua Hifi Formula [on review]
Preamplifier: Nagra Jazz, Esoteric C-03, Vinnie Rossi LIO (DHT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, F5, F6; Crayon Audio CFA-1.2; Goldmund Job 225; Gato Audio DIA-250; Aura Note Premier; Wyred4Sound mINT; AURALiC Merak [on loan], Wyred4Sound SX-1000R [on review]
Loudspeakers: Albedo Audio Aptica; Sounddeco Sigma 2; EnigmAcoustics Mythology M1; soundkaos Wave 40; Boenicke Audio W5; Zu Audio Druid MkV & Submission; German Physiks HRS-120; Eversound Essence
Headphones: Audeze LCD2/LCD-XC with balanced Forza Noir hybrid cable; HifiMan HE-1000; Sennheiser HD800 with Forza Noir cable; Final Sonorous III/VI with balanced ALO Audio cable; MrSpeakers Alpha Prime with balanced Forza Noir hybrid cable; Beyerdynamic T1/T5P with ALO Audio cable; Meze 99 Classic
Headphone amps: COS Engineering H1; Vinnie Rossi LIO with DHT module; 2 x Questyle CMA800R for mono balanced drive
Cables: Complete loom of Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Arkana Research XLR/RCA and speaker cables [on loan]
Power delivery: Vibex Granada/Alhambra on all components
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Krion amp stands
Sundry accessories: Acoustic System resonators, Verictum Silver X block on preamp and amplifier
Room: Rectangular 5.5 x 15m open floor plan with two-storey gabled ceiling, wood-sleeved steel trusses and stone-over-concrete flooring
Review component retail: $3'500

Pass Labs. For power amps of the class A persuasion, Nelson Pass has become a living American legend. For preamps and phono, the Pass Labs man is Wayne Coburn. Desmond Harrington, an Irish transplant from Castletownbere in County Cork, handles their industrial design. Using basic deduction, the setup seems to be that Wayne is their low-level signalist whilst Nelson is the resident high-level man. Which begs the question. Just who had his hands in/on the HPA-1? Most designers approach a headphone amp as a low-level circuit. Given headfi's general power ratings and high(er) load impedances, that's far from irrational, particularly with regards to mandatory noise levels (zero!) when transducers are practically hardwired to your pink bits. Keep the gain low and with it, the noise out. Alas, first AKG's infamous K-1000 then HifiMan's no less infamous HE-6 turned up the heat. They demanded a good handful of real not fractional watts to stand at ramrod attention and be heard. Suddenly headfi was on 2A3/300B amp turf. Wowsa! That opened doors to treat such amps as more specialized power than miniature preamps. So Nelson or Wayne? Neither. The man behind the HPA-1 is one Jam Somasundram. Originally from Malaysia, then the UK, his 35-year connection to Nelson had him finally join their left-coast team in Auburn/California after a 3-year stint as director of engineering at Cary Audio's right-coast digs. Of course the question still stands. Did Jam treat his first Pass project as more of a compact preamp or ultra low-noise flea-power power amp? That his MO would have to be class A either way seems rather a given. Likewise for not using tubes.

As you already gleaned from these sexy stock photos, our blocky bloke is quite the no-frills affair. It says no to 3.5mm, to 4-pin XLR and to dual 3-pin XLR on the front; and to XLR on the back. Just so, it double teams as a basic two-input preamp, sans remote but separate from the locking Neutrik 6.3mm port by way of a direct path triggered by a matching front panel control. Hence the HPA-1 is a bona fide albeit basic 2-in-1 headfi/preamp. That leaves 3-in-1ness to competitors concerned over cramming a DAC of varying connectivity into the same box. On said count, the Pass plays it more purist. It's purely analog. Then it drops the goods into a battleship casing of thick aluminium panels which are proudly bolted together in the good ol' US of A. Machines like Taiwan's COS Engineering H1 go more glam on their extruded casing to show zero visible fasteners but on the insides rely on a very compact SMPS and op-amp outputs where the HPA-1 is fully discrete.

On power, the HPA-1 maxes out at 3.5 watts into 20Ω. That's down to 200mW into 300Ω, making for 6W power consumption. Bandwidth is a wide 10Hz to 200kHz. Zout into headphones is below 2Ω and about 50Ω on the pre-outs. Weight and dimensions come to a kilo per headphone jack millimetre (6.35kg) and 28x11.5x33cm WxHxD. The simple two-stage circuit combines Toshiba Jfet inputs with a direct-coupled Fairchild Mosfet output current buffer for 8dB of voltage gain and THD+N of <0.005/1V out. Volume control is an Alps pot, the power trafo is a twice-shielded specialty toroid, power rails are 24V and supply capacitance is a studly 40'000µF. The power supply exploits CRC filtering and discrete no-feedback regulators. The only IC in the entire design is a DC servo. From these stats, the Pass looks more like a compact integrated amp than preamp. Since it does double as an actual preamp, one expects rather unusual drive and supreme SN/R performance in such use to compensate for the couch potato insult of no remote. To find out just how its designer views the design, I fired off some questions at Jam who quickly fired back.