Country of Origin
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, 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, HifiMan Susvara; Loudspeakers: Qualio IQ [on loan] Cables: Kinki Studio Earth, Furutech; Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps, 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, LessLoss Firewall for loudspeakers, Furutech NCF Signal Boosters; 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; Preamp/filter: Lifesaver Audio Gradient Box 2; Amplifier: Kinki Studio EX-M7; Headamp: Cen.Grand Silver Fox; Loudspeakers: MonAcoustic SuperMon Mini + Dynaudio S18 sub; Power delivery: Furutech GTO 2D NCF, Akiko Audio Corelli; Equipment rack: Hifistay Mythology Transform X-Frame [on extended loan]; Sundry accessories: Audioquest Fog Lifters; Furutech NFC Clear Lines; Room: ~3.5 x 8m
Desktop system: Source: HP Z230 work station Win10/64; USB bridge: Singxer SU-2; DAC: Sonnet Pasithea; Headamp: Kinki Studio THR-1; Speaker amp: Crayon CFA-1.2; Speakers: Acelec Model One Headphones: Final D-8000 & Sonorous X, Audeze LCD-XC, Raal-Requisite SR1a on Schiit Jotunheim R
Upstairs headfi system: FiiO R7, COS Engineering D1, Cen.Grand Silver Fox; Headphones: Raal 1995 Magna, 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: €799
Today's 7½wpc/32Ω fully balanced class A amplifier with R2R volume and hi/lo bias on two parallel pairs of output transistors is aune's most upscale headfi amp. That makes it the natural-borne playmate for their recently reviewed SR7000 dynamic headphone. The same catalogue includes an amplifier with integral DAC, USB bridges, a standalone DAC and sundry portable players. What's more, aune work well below the €1K mark for all models, no exception. It's a key part of the aune story. They position themselves as a brand for the people not aristocracy. Words to that effect marked my full-length review of their €639 'phones. That makes suitable background reading to avoid repetition. Having enjoyed my time first with the sealed aune then its open-backed €329 AR5000 sibling, I subsequently suggested to my factory contact that following up with their best amp driving their own cans could be interesting?
Between the bolt holes marked with the screw icon, we see four open holes where the heatsink torques down onto the 16 PCB-mounted transistors.
"Yes, good idea, next month we'll send you our new S17Pro for review once we have it." And there it is, the li'l 3-letter word new. Naturally we want to know what's different. Before finding out, I suspected that one thing to undergo certain revision was the cooling of the output devices. Some commentators of the original had reported that in 100mW high-bias mode, they could only operate the S17Pro for 30-60 minutes before internal heat protection kicked in to not exceed 69°C and automatically switch down to low bias¹. Meanwhile 50mW mode worked 24/7.
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¹ Some reviewers erroneously conflated low bias with class AB mode. This amp operated in class A regardless. The difference was the amount of bias applied to the output devices which sets how hot they run and their load line which determines their distortion behaviour. But even in 50mA mode, they never turned off. They just dissipated less heat.
Others reported no high-bias issues whatsoever. For those who did, was it due to broad variations from unit to unit? Was the shut-down C° value in the micro processor too low for the wide range of ambient temps around the globe? Was the mechanical coupling of the internal heatsink to the output transistors insufficient to require a larger contact patch or firmer clamping force for more effective heat transfer? Whatever those details, had anything else occurred to aune's design team once they were tasked to revisit the S17Pro's original circuit?
