I don’t think I’ve given PTA Senior Contributing Editor Grover Neville enough credit about this in the past, but he really does an excellent job when it comes to discovering new and worthwhile manufacturers for us to explore. Grover turned us on to ampsandsound, which is one of our favorite tube amplifier brands, and he was the first to review Allnic Audio, which now comprises a big chunk of my reference rig. Grover was also the first to take a chance on a company named Bakoon International, which later changed their name to Enleum. (Enleum comes from the mind of a man named Soo In Chae, who started building compact audio devices in a dorm room in Pennsylvania.) Right now I’m spending time with the Enleum HPA-23RM headphone amplifier and I have to say, once again, that Grover is absolutely spot-on when it comes to the good stuff.
Words and Photos by Marc Phillips
The Enleum HPA-23RM is very small, about the size of a paperback novella, which surprised me. It reminds me of the portable headphone rigs that dominated the market a couple of decades ago, the little systems that included a compact amp, a matching battery unit and a bag to carry it all. It retails for $3,000, which seems expensive at first until you learn about all the technology inside, or when you listen to it for the first time.
Minutes after plugging it in and taking a listen, I started coming up with plans to take this on the road with me. (At the end of a long day on the high-end audio show circuit, I often wish I had a nice headphone rig in my hotel room so I can fall asleep.) Enleum HPA-23RM, my trusty Cardas A8 earbuds all hooked up to my laptop (or even my iPhone, since the M in the model name stands for mobile) and streaming Qobuz? It sounded like a plan. The Enleum, after all, can run continuously off an AC wall outlet or a USB C port, or you can get 3.5 to 5 hours off the battery.
Despite its diminutive size, however, the Enleum is a pretty serious headphone amplifier capable of stunning sound. In my opinion, it’s quite notable for its combination of strengths.
Inside the Enleum HPA-23RM
When Grover reviewed the Enleum AMP-23, he found that this 25wpc integrated/headphone amp was just as good with a pair of speakers as it was with a pair of cans. Its great reputation, of course, is solid with the head-fi experts, so I knew that trying out the HPA-23RM would be intriguing to say the least. That’s because I’m trying to explore the world of head-fi for as long as I can this time around, because so much happened in the years when I turned my back on this scene and I don’t want that to happen again.
I’m not sure I want to go on and on about the size of the Enleum HPA-23RM since it merely gets me thinking about all the novel yet practical ways I can use it. (For the record, the HPA-23RM measures just 4.5″ by 6.5″ by 0.9″, and it weighs just 26 ounces.) But here’s a fact that makes its diminutive side even more of a triumph–the Enleum is actually two amplifiers in one due to its voltage and current outputs. The voltage output circuit is borrowed from the AMP-23R integrated, which uses MOSFETs controlled by a JET2 Bias circuit, and the current output–which offers a surprising one watt per channel of power output–is an improved version from the Enleum HPA-21, which uses bipolar resistors. What enables all of this sophisticated circuitry to fit in such a small chassis? Enleum includes new advances in the battery power supplies, including thermal efficiency practices, to keep all the circuits operating safely within their parameters.
The Enleum HPA-23RM might be small, but the attention to the detail of this design is thorough. The HPA-23RM is able to transfer the heat from its circuits through the efficient use of heat sinks. The Ensence circuit module, with its discrete transistors and zero feedback design, comes straight from the AMP-23R, which costs about twice as much as the HPA-23RM. The battery circuit has been designed to extend battery life while reducing the amount of Li-ion batteries needed to just two–thanks to both a new battery power supply design and ultra-low noise regulators. The HPA-23RM also employs solid state relays in the attenuator circuit, which reduces noise and allows for varying sensitivity for all sorts of headphones.
Best of all, the level of fit and finish of this little box reflects the sophistication of what’s inside. Tolerances are extremely high, and the entire design is focused on a simple and intuitive user interface, something I find particularly attractive. In high-end audio, real estate is often a secondary consideration. You make things as big as they need to be. But in this case, the Enleum HPA-23RM is a master class in purpose, efficiency and, of course, performance, which is why it won two major industrial design awards from Red Dot and iF.
Set-Up
It’s funny to talk about the “set-up” for the Enleum HPA-23RM headphone amplifier. What’s to set up? Plug it into a wall outlet, connect it to a source, and slip on your favorite headphones. Easy as pie.
I did use the Enleum in a number of configurations, however, mostly because I’ve set up that separate area in my living room for side projects, like listening to headphones, or breaking in review gear, or testing out equipment combinations in advance just to see if they’ll work before I start moving around the heavy stuff.
First of all, I used three pairs of headphones with the Enleum HPA-23RM–the ZMF Atrium Closed headphones ($2,499), the ZMF Calderas ($3,499) and the Bowers & Wilkins Px7 S2e noise-cancelling wireless headphones ($399). For my RCA interconnects, I picked the Allnic Audio Zeros ($4,000/pr) because they might just be my favorite ICs of all. Sources varied–I used everything from the Unison Research Unico CDE CD player to the Music Hall Stealth (with ZYX Bloom 3 cartridge and the Hagerman Audio Labs Piccolo MC head amp) to the Innuos Pulsar and the internal DAC of the Matrix Audio Element X2 Pure network streamer.
As I mentioned, everything was easy to hook-up, and in no time I was curled up on the sofa and listening to my favorite tunes. If I had one complaint, it’s about something that’s completely in service to the small size of this amp–the volume control. As you can see, it’s also tiny and it’s inset into the casework so only a small portion of the knob is accessible. I found it difficult to manipulate this knob in a smooth, predictable manner, which is something that’s concerning when you have a pair of headphones strapped to your skull. A bigger knob isn’t the solution, because it would ruin the whole ergonomic flow of the Enleum HPA-23RM. Perhaps the inset, which gives the Enleum a modern, streamlined look, could be modified slightly. Or perhaps I can stop being so darned clumsy with all these little controls.
Enleum HPA-23RM Sound
First of all, there is a difference in the sound between the voltage and current output, as Soo In Chae explains: “Voltage and current output differ quite a bit in sound quality, especially with dynamic headphones whose impedance curves usually vary, whereas planar magnetic headphones impedance usually remains flat.” I briefly tried my Cardas IEMs with the voltage output, but most of my testing involved the ZMF headphones through the current output.
From the first moment it was plugged in, the Enleum HPA-23RM possessed a confident and calm manner that instantly endeared itself. The high frequencies were extended but never harsh, the lower frequencies had plenty of heft (the ZMFs deserve part of the credit here because they’re so splendid with bass) and the presentation as a whole was one of clarity and detail.
I have one general observation of the sound–the tonality is somewhat akin to the inboard headphone amp in my Naim NAIT 50. That’s certainly not a bad thing–I find the Naim headphone amp to be linear and dynamic and truly revealing of the source material, so much so that I consider it my personal reference for now. It’s certainly not the NAIT 50’s fault that it’s also attached to a stunning integrated amplifier, and so far I’ve listened to many inboard headphone amplifiers from companies such as Burmester, AVM and BAT that compete with dedicated, stand-alone headphone amplifiers.
The Enleum HPA-23RM did diverge with the Naim NAIT 50 in one important aspect–the sweetness of the high frequencies. During my recent foray into head-fi, I have encountered harsh recordings that can dispense a fresh headache with alarming force. The Enleum, however, had that sweet extension in the treble that accompanies high-resolution recordings. Hi-rez treble isn’t just higher, it has enough layers and textures and space to ameliorate anything that might sound too loud or too harsh. There’s space in the music, because there’s headroom in the circuitry.
The lowest frequencies were also impressive and visceral. The ZMF Caldera, in particular, excelled in this regard when connected to the Enleum. I constantly felt the deepest bass in my torso, something that rarely happens to me when I’m listening to headphoe rigs. (I usually feel the beat from within my head, which isn’t always the most natural perspective.) As Soo In Chae adds, “This is one big strength of the HPA-23RM’s current drive circuit for fully driving planar magnetic headphones.”
Perhaps the most surprising part about the sound of the Enleum HPA-23RM was also noticed by Grover–there is an almost tube-like sweetness to the Enleum sound, a warmth that differentiates it from the more “neutral” Naim headphone amp. Switching back and forth between the two amps, I felt the upper midrange and lower treble of the Naim was just a little drier than with the Enleum.
Listening Sessions
I started off with Radiohead’s Kid A, because I’ve found moments within it that help me to evaluate review gear. I often focus on the title track, which contains those distorted vocals buried deep in the mix, and because there are a couple of bass synthesizer notes that are uncommonly deep. It takes a good playback system to clarify the words being said–it’s basically a Pied Piper story–and to dig out that bass so it doesn’t sound so soft and distant. With the Enleum HPA-23RM, certain lines leapt out at me like never before–We’ve got heads on sticks/And you’ve got ventriloquists–and those bass notes were full and preserved as a whole rather than a single fundamental.
Moving on to one of my favorite songs on the album, the moody and somewhat epic “How to Disappear Completely,” I was able to focus on Ed O’Neill’s steady and constant bass riff, which usually seems simple and repetitive on lesser gear. The Enleum carved those bass lines out of the mix so I could hear more than just the same notes, repeated for the entire length of the song. I could hear his fingers slide up and down the strings, and I could hear his tangents in their full glory–perhaps for the very first time.
On Henning Sommerro’s Borders, released by 2L Recordings, the Enleum easily captured the dynamics of this lively and energetic recording. This is a busy work, with plenty of unorthodox choices for solo instrument including a harmonica and a pan flute, and it’s easy for some amplifiers to sound overwhelming when faced with those complex passages. With the Enleum HPA-23RM and the ZMF Atrium Closed headphones, Borders was unusually easy to digest–so much so that I preferred to review the album with this configuration in place. While the Enleum is so proficient at gathering detail and preserving dynamic contrasts, I never had any worries about listening fatigue. The overall presentation was so immense and clear that I could determine the structure of this ambitious work while succumbing to the charm of this truly beautiful music.
Conclusions
If the last year has seen an influx of small yet potent boxes in my systems–think of the Bob’s Devices Sky 20-S step-up transformer, the Hagerman Audio Labs Piccolo MC head amp and, mostly notably, the Naim NAIT 50 integrated amplifier–then it’s also provided a compelling argument for keeping things simple and out of the way. (It’s obviously a passing trend after receiving big and heavy gear such as the YG Acoustics Sonja 3.2 loudspeakers at 320 pounds each, the Burmester 909 Mk. 5 power amplifier at 157 pounds and even those gorgeous Songer Audio S2 field coil speakers, which weigh in at 150 pounds each.) Considering that I’ve been battling sciatica after all my air travel last October, compounded by a tailbone injury incurred by small compact pine cones that act as rollerblade wheels if you’re not paying attention, I appreciate the little stuff as long as it sounds special.
With the Enleum HPA-23RM, the smallness of the unit is certainly appreciated. But I found myself enjoying the size, as well as the stunning performance, because it gave me a steady stream of ideas on how I could use it in different ways. There are times when my tabletop headphone system is complex, with many boxes and cables, and I loved how I could assemble such a high-performance rig with just the little Enleum, headphones, a pair of interconnects, and whichever source I wanted to try. This is a complete system that could wind up on a nightstand so that I could indulge my favorite listening habits, such as falling asleep with headphones on–just as I did when I was teenager and my dad was home. (He couldn’t object to Ramones and Hüsker Dü in his house if he couldn’t hear it.)
In terms of sound quality, the Enleum HPA-23RM was a polar opposite to tubed headphone amps such as the Audion Silver Night, which employs 300Bs for a smooth, velvety and warm sound. Compared to the more linear headphone amps I have such as the inboard unit in the Naim NAIT 50 and the Austin Audio Works The Black Swan, the Enleum could sound very similar–but I always felt that I was getting a touch more detail.
In other words, Grover Neville was right, once again. The Enleum HPA-23RM is a great-sounding headphone amp, and it deserves my highest recommendation.
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