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This review first appeared in November 2022 on fairaudio.de. By request of the manufacturer and permission of the author, it is hereby syndicated from the German original to reach a broader English audience. Ed.
Reviewer: Jörg Dames
Digital sources: Norma HS-DA1 PRE, Keces S3,Melco N50-S38, SOtM sMS-200 ultra & sPS-500, Volumio Primo
Preamps: Funk MTX Monitor V3b-4.3.1, Monitor V3b-4.2.1 (upgraded V3b), LAP-2.V3 (upgraded Lap-2.V2)
Integrated amplifier: Abacus Ampino
Power amps: Bryston 7B³, Norma Revo PA 150
Loudspeakers: Wilson Audio SabrinaX, Sehring 903 Serie 2
Cables: Kimber Carbon 16, HMS Armonia, WSS Platin Line LS4, Real Cable BW OFC 400, HMS Fortissimo, Straight Wire Virtuoso Digitalkabel, AudioQuest Carbon, Boaacoustic Silver Digital Xeno, BMC Pure USB1, Kondo KSL-ACc Persimmon, HMS Energia Suprema, Tellurium Q Black, Quantum-Powerchords, Swisscables Reference
Power delivery: HMS Energia MkII
Rack: Lovan Classic II
Room size: 29m² with 3.3m ceiling
Review component retail in Germany: €7'490
"It's so tiny and cuddly. And those cute clattering little footers." If that's your takeaway after one quick glance at Enleum's AMP-23R 2022, do I have news for you. This is a real wolf in sheep's fleece. That theme fits the upcoming carnival season; and ongoing trend for compact extremely high-zoot hifi kit. On that score this rates as a variable power amp, purist integrated and high-end head amp. It's all folded into a 23x23x5.5cm case which Audiodomain of Germany distribute for €7'490. Never heard of Enleum? Don't fret. Me neither. The brand is only a year old. Nevertheless it's far from a newbie. Rather, it goes back to 2009; or decades farther depending on how one defines it. Enleum is Bakoon International reborn. 13 years ago they began to globally market Bakoon Products which until then had sold just within Japan. Fairaudio readers should recognize the Bakoon name since we already reviewed their thoroughbred HPA-01 headphone amplifier with the firm's proprietary Satri circuit.
Enleum operate two headquarters: San José in California takes care of design and marketing, R&D and actual production happen in the Gyeonggi-do province of South Korea's north west. The amp's high-revving engine combines low negative feedback with real-time monitoring. Even though likely trademark reasons no longer apply the 'Satri' moniker, it's still a low-impedance current-mode circuit ideal to process high-bandwidth signal since inductive reactance increases proportionally with frequency. Even though the formal spec only says 10Hz-100kHz without usual -3dB tolerance to not seem particularly extended, company boss Soo-In Chae emphasized that their circuit measures clean out to 1MHz just with reduced power. Granted, at first glance that doesn't seem too stringent but let me tip my hat early: the little Enleum was one of the 'fastest' amps I ever met so listen carefully. Compared to earlier production runs, the 2022 version upgraded its power supply and input buffer sections. The output stage works one pair of p/p Mosfets in class AB bias per channel. I measured pleasingly low 23-watt idle consumption.
Soo In sees as one of their main advantages over conventional class AB amps a complex hardware/software interface which monitors the bias voltage on their Exicon output transistors in real time. This involves A/D⇒D/A converters outside the signal path. Known as JET2 bias, this control circuit's first sighting dates back to Bakoon's AMP-13R precursor. The updated Enleum variant promises particularly precise and quick control of the transistors' ideal operating point so higher fidelity from lower distortion. Just don't call it an integrated amplifier. Whilst the technically complex volume control contributes to lower distortion, the apparently classic rotary knob really isn't a traditional potentiometer. Little clicks indicate a relay-based circuit and occasionally there may even be subtle pops through the speakers. "That's completely normal," we're assured, "and a small compromise for best performance". In addition to ten relays, this volume control includes 20 resistors and the complex firmware system calculates the exact resistive value required for the desired volume. That value doesn't cut the signal like a conventional integrated with a preamp section but sets the amplification factor of the gain stage. Strictly speaking this is a variable-gain power amp not an integrated despite the two line-level RCA inputs, single-wire 25w/8Ω WBT speaker terminals and proprietary Enlink BNC inputs. There's even a 6.35mm jack which auto-mutes the main outputs to steer the amp's full power at headphones so a solid 4 watts into 50Ω. "Any load impedance is fine. It's a very powerful headphone amp. Just be careful with high-sensitivity in-ears." Enleum conveniently offer two gain settings for headfi mode.
This asks an obvious question. What was more important to R&D, speaker or headphone drive? "Both were equally important," explained Soo-In Chae. "We wanted the AMP-23R to be the best possible compact amplifier for either use." Of course any amp powered by just an 85VA transformer demands more care when choosing the right speaker than headphone. Incidentally, Mr. Chae drives Wilson TuneTots with his AMP-23R in a 28m² living room. Those spec out at just 86dB/W/m. After my own extensive testing, it's a counterintuitive combination I can still appreciate sonically and electrically since my own Sehring 903 Mk2 were no more efficient themselves. But we'll get to teammates in a moment. First a scaredy-cat question for Enleum: does the AMP-23R run protection circuits against clipping and overload? "There are four different protection circuits related to over/under voltage, DC output current and temperature. The combination of these four protection modes is sufficient for a compact amp. For example, our thermal monitor loop would shut down the amplifier if it overloaded for any period of time. The DC-offset protection would detect still longer clipping."
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