For Ears and Years - Enleum AMP-23R Review

Overall Score 95/100
Sandu Vitalie Amplifiers

My Video Review:

Hey folks, today isn’t an ordinary day, oh no…it’s a day dedicated to enlightenment, to discovery, to purity of mind and soul, dedicated to a perfect equilibrium in everything that surrounds us. Owing to a specially tailored amplifier in all regards, starting with its working principle, form factor, ease of use, feature set and finishing with sound quality. Get it out of the way and look from a different perspective, as today I’ll be trying one of the most expensive, fully-discrete headphone and integrated amplifier that I put my hands on. It goes for a little over $6000, but let’s get it over and enjoy the realm of enlightenment.

In many cultures around the globe, but especially in Far East countries, minimalism is an art movement interpreted as a reaction against abstract expressionism. Often times we don’t know why less is more, but when that perfect balance strikes us…we can feel it instantly and stop in an awe moment, declaring it as the purest form of perfection.

Perfection is undoubtedly hard to achieve, as it requires a vast experience, exquisite craftsmanship, deep understanding and knowledge, vision and years of dedication. Perfection can’t be fulfilled with the first trial & error and when a product appears to be almost perfect, years of extensive polishing will need to pass, multiple iterations would follow, maybe even rebranding your banners and changing somebody’s view will be needed…until achieving a flawless product.

Enter, Enleum’s first road opening product dedicated to the realm of high-end audio. Even if on paper AMP-23R looks like their first product, its circuit board carries a strong DNA, traced back to its ancestors as Bakoon AMP-11R, HPA-21, AMP-12R and AMP-13R - which caused quite a stir a few years prior for their original design philosophy and sound signature.

Enleum isn’t a continuation of a finished book, I see it as a brand-new journey where the previous one ended. All Enleum’s units are designed in California and made in South Korea, their brand name glues together ENLightenment and EUM - which stands for sound in native Korean. AMP dictates its purpose; the following digits will be telling about its size & generation and the final R - reflects about its Reference status. While having an identical footprint to its twin brother AMP-13R, thanks to an all-new chassis and thermal heatsink, they’ve launched a brand-new product that fits the next generation of audiophile minimalists, spotting a one-of-a-kind look that was (already) awarded with the iF Design Gold Award in 2022 and Red Dot Award in 2021. If you’re a returning reader, you already prepared a cozy chair and a refreshment and if you’re new to our independent publication, then please enjoy our customary way in dealing with audio-components. AMP-23R will be put through its paces in both a headphone-based & stereo setup and in the latest chapters it will be compared side by side with world’s best current production headphone amplifiers.

Q&A Session with Enleum’s CEO

For us, AMP-23R reinvented the wheel in terms of amplifier design, it felt so radical and different that I felt the urge to know more about it…and about the people that made it.

Sandu Vitalie (Soundnews) Q1: Let’s start with simple things. Can you tell us how it all started, what was the spark that ignited the fire?

Soo In Chae: Like everyone in the industry, I’ve loved music from my childhood and I’ve been always trying to find a way to enjoy listening even more. During my college years, I was studying abroad by myself and lived in a small dormitory trying to find the best possible compact audio systems, then it naturally got me into a simple, compact, and yet no compromise system for both headphones and speakers. After graduation, with my engineering background and work experience in a high-tech company doing various successful engineering and design projects, I was then confident enough to decide that I can gather all the right tools to make something special and began my journey to form Bakoon International in 2009.

Q2: Building a brand-new identity with Enleum looks like a daunting task, why not walk the same path, paved by the good-old Bakoon International? Starting fresh isn’t for the faint of heart, as you need new marketing, advertising, social media, not to mention additional research and development costs.

Soo In Chae: Indeed, we’ve been working under our old name for some time, but as we’ve already moved away from Bakoon, and have been designing and engineering on our own since 2016, there has been a need to distinguish ourselves more. I’ve worked with some amazing people around the world for our rebranding process and since we have maintained our close working relationship with all our partners, it has been a smooth transition into our new brand, Enleum.

Q3: We’re still scratching our heads with this one. Why single-ended and not a balanced input to output design? Why RCA inputs and 6.35mm (1/4”) headphone outputs?

Soo In Chae: As our circuit is current based, it holds many advantages over conventional voltage-based circuits. It is simply not so necessary to rely on balanced circuits to achieve the performance we need. As such, we can simplify and concentrate on what is more essential for the overall performance, with our circuit designs and ideas.

Q4: Those Enlink inputs sitting exactly in the middle are trying to tell us something? Is a complimentary D/A converter and/or wireless streamer around the corner? Could you tell us more? Pretty please.

Soo In Chae: We have been working on some DAC projects in the past, but this has been taking a bit too much time with the AKM factory fire and other chipset shortages. With all the rebranding process and our AMP-23R popularity, we have not had too much time to work back on these source equipment projects, but they are in our mind and we know many people are waiting for this, so hopefully soon!

Q5: Do you consider AMP-23R more as an ultimate headphone amplifier, as a specialist integrated amplifier or as do-it-all wonder-box that could work equally well with speakers and headphones alike?

Soo In Chae: No, the AMP-23R is not just a headphone amplifier. It represents our best possible circuit design for a reference grade “compact” amplifier. This is intended to provide our flagship level circuit performance for both headphones and speakers that are efficient enough with 25 watts. Despite its size and spec numbers, many will be quite surprised how well it can drive speakers too.

Q6: A lot of amplifier designers are tuning their gear with the help of a single, maximum two headphones or loudspeakers. Can you share with us which were the headphones and loudspeakers that were used the most while planting the seeds for the brand-new AMP-23R?

Soo In Chae: We don’t design and tune for any certain models, but as an audiophile myself, I have a few systems around that I enjoy all with the AMP-23R. For speakers, I use Soundkaos VOX 3a and Wilson Audio TuneTots in my main system, or Dynaudio Special Forty and Harbeth P3ESR XD in my bedroom. For headphones, I just have too many to state, but we’ve had a good working relationship with Audeze from way back and I basically have all their headphones. Of course, the AMP-23R sounds magnificent with the Hifiman Susvara and I’m sure many people already know about this.

Q7: AMP-23R is skipping traditional amplifier design in terms of size, power consumption, power output and most importantly, sonics. Was all that made on purpose? Was me-too out of the window when designing the little one?

Soo In Chae: We are always trying to make something that is unique and “outside the box”. It’s simply not necessary to repeat something that already exists. Indeed, we are now well known for our compact amplifiers like the AMP-23R, but we did introduce bigger amplifiers and various source equipment in the past and you will see some exciting things coming from us soon. Of course, I’m a bit obsessed with minimalism, simplification, and design qualities, so these are the most important elements for our designs.

End words: Thank you for thinking outside the box, for your ambition, creativity and for accepting our Q&A session! The honor is all ours.

Soo In Chae: Thank you for your kind words, and I’m happy to share our exciting journey with you and your readers.

Unboxing Experience

If you ever got to unbox an Apple product, you already know how much energy and thought is put into their packaging, as every single square inch is used for maximum efficiency. The same amount of energy was put into Enleum’s firstborn. Forget about mindless oversized boxes, as you’re getting exactly what was needed to safely pack and ship a beautiful looking unit. My first-hand experience is more important than the unboxing itself and seeing a textile bag embossed with Enleum’s logo surrounding the unit already got me excited for what’s to come.

Naturally, AMP-23R was surrounded by a thick card board box, filled with foam for a better protection during shipping. Its remote control sits near it, including a detailed user manual. A smaller box contains its anti-vibration feet, custom designed in collaboration between Enleum and TAKT for the AMP-23R alone. You won’t find a power cord, but I don’t see the reason of using a stock power cable with such a high-profile amplifier.

Design & Build Quality

While it looks like a rectangular heavy-duty metal box, there are many small details that are adding a high-end flair to it. AMP-23R showcases a high-quality craftsmanship, inheriting Bakoon International’s traditional esthetic features. I’ve seen plenty of devices by now that had metallic dissipation fins, but most of them were plain and simple. These guys added a touch of refinement, making them unique and beautiful looking, reminding me about minimalist industrial designs. As of right now, they are offering it in matte dark-grey only, but it would be something to behold if cherry red, dark blue or pure white finishes would be added in the future. I’m sometimes mentioning the Wife Acceptance Factor (WAF for short) in my reviews, as units that will be staying in the living room need to be approved first by the cat eyes of our beloved. Some units didn’t cut it, others were on the edge of being rejected and just a handful passed this test with flying colors. After explaining that it would replace two metal boxes in the living room and another one in my office, she winked and nodded, grating me a safe passage. We can all exhale and relax, as AMP-23R just got top WAF points!

Under it you can see four rubber feet placed in perfectly-cut round spaces and besides them, Enleum is supplying three CNC machined anti-vibration feet that employ Base Isolation Device technology. These are no longer optional as every single AMP-23R will be getting them. These share the same engineering principles found in skyscrapers and bridges, where external forces such as winds and earthquakes would have to be cancelled out. I’m putting its anti-vibration shoes when it hops in my stereo and I like its look without them in my headphone setup. Forget about bolts and screws all around it, as most of them were moved to its bottom, excluding unnecessary elements for a neat looking device.

It measures 230 x 230 x 55mm and weighs four kilos, making it the tiniest high-end integrated / headphone amplifier I had the pleasure of licking…er…putting my hands on. In the end, we’re getting a spectacular looking unit that focuses on perfection with minimalist originality and beauty. Fit and finish sits at the highest level I’ve encountered with personal audio and that’s all you need to know about it.

Controls & Connectivity

AMP-23R has the simplest front panel I’ve seen in ages, spotting a single 6.35mm (1/4”) headphone jack, an On/Off button that can work as an input selector and there’s a volume wheel to its right.

On its back you’ll find an AC inlet, two pairs of RCA inputs, a pair of proprietary Enlink inputs - put in place for their upcoming D/A converter (just an educated guess) and a pair of speaker terminals will be sealing the deal.

Technology Inside Enleum’s AMP-23R

First thing’s first, you’re looking at a fully-discrete transistor-based integrated and headphone amplifier that completely discards negative feedback. Its newly developed Ensense Circuit was born from years of expertise acquired from previous generation technologies, concealed into compact input stage modules called Ensense. These modules feature an ultra-fast and ultra-wide frequency response that would never press the brakes when it comes to dynamics.

Its output stage is based on oversized EXICON Mosfets that are controlled by their JET2 BIAS. They called it JET as an abbreviation of Jet, Exact and Tracking, involving highly complex ADC, DAC and MPU circuits with advanced software technologies. The JET bias was developed in order to maintain the highest possible efficiency, while significantly increasing the output stage’s stability. It tracks the bias at all times, enabling ultra-fast correction of the bias and offset of the output stage, resulting in a much more precise control of the EXICON Mosfets.

One of their original goals was creating an ultimate headphone amplifier thanks to Ensense modules and JET2 bias that led to a zero-loss amplification factor change. The highest-grade OMRON analog relays are also on board, offering a precise volume control, so you can experience every single detail and nuance coming from your source, something you won’t see on regular headphone amplifiers.

There’s an oversized linear and regulated transformer controlled by a software embedded in an MPU, significantly reducing the number of parts, highly boosting efficiency throughout the circuits. Its digital and analog circuits are fully isolated from each other to minimize interference.

AMP-23R offer 25 Watts per channel in 8 Ohms and 45 Watts in 4 Ohms, meant to be used with higher efficiency loudspeakers. Its headphone amplifier is no joke with 4 Watts per channel in 60 Ohms, this puppy should drive every single headphone in existence with plenty of headroom remaining on tap…but we’ll see about that very soon. There’s a 22.5dB gain for loudspeakers and headphones (on high-gain) and 7dB on low-gain to be used with higher efficiency headphones and I believe it’s the right time for a long listening session.

Test Equipment

AMP-23R shoots for you stereo and head-fi battle station as the only driving force behind ALL your diaphragms and that’s why it was used in two distinct setups:

  • As a high-end unit, we’ve built a high-end rig around it in my office. A Denafrips Gaia DDC will be cleaning up the signal coming from my PC, followed by a Denafrips Terminator Plus DAC. AMP-23R was driving a wall of headphones, ranging from affordable dynamic-driver cans, portable over-ears and finishing with high-end planar-magnetics.
  • Later on, it was moved to the living room, connected to a Gold Note DS-10 Plus streamer and DAC, replacing two Benchmark AHB2 mono amplifiers and trying to move a pair of KEF Reference 3 loudspeakers.

Okay everyone, I’ve prepared a glass of wine, my body and soul are ready for some well-deserved music, so let’s hit some eardrums!

Sound Performance

I. Preliminary Sound Impressions

AMP-23R is being used for about two weeks now, one week it was singing tunes with headphones attached and another one in my stereo, so I could get a better feel of its sound signature. When assessing such a unit, I feel that the spec sheet doesn’t matter as much and let me explain you why. How can a such low-powered unit fully drive a pair of KEF Reference 3 standfloor, putting a higher authority in the bass, a higher density in the midrange, a gentle delicacy in the treble and still leave ~50% of headroom is beyond my understanding and the same can be said when driving the most inefficient headphones out there - the mighty Hifiman Susvara. While only 4-Watts are being offered in 60 Ohms, it easily drove them with an absurd amount of power always remaining on tap. I know my Susvara (that I nicknamed Suzy) very well, as for more than a year now, they became my no.1 headphone, helping me out testing new D/A converters and headphone amplifiers.

Suzy is not only a very hard to drive headphone, but also a difficult task when trying to highlight their inner beaty, as they will shine only on rare breed amplifiers. Enleum’s first attempt didn’t sound like traditional transistor-based amplifiers that were sitting near it, with AMP-23R there’s a peace of mind, an easiness that I don’t remember getting from such units. If I would describe its sound signature in a few words that would be: total control of the drivers, tonal accuracy, a higher bass and midrange density, an incredible sense of pace, rhythm and timing, while putting more texture on top of every musical note. It’s like ordering a single cup of ice-cream, but getting three cups in return with some extra topping on top. There’s simply so much more in terms of texture that surrounds your music, there’s so much more nuance that was lost in transit with regular amplifiers, the whole frequency response got a very different meaning with a unit like this. It’s no longer about technicalities, linearity, cleanness, speed and impact, it’s more about inner detail, layering and about the third eye that just opened while listening to music.

Enleum’s first creation added more meaning to my music, there isn’t only more inner detail, but there’s more music flying around, more smoothness and weight can be felt when music passes by, there’s definitely more of everything, connecting with my tunes in mere seconds, something that only world-class hybrid or tube-based amplifiers were able to achieve in the past.

While incredibly clean and transparent sounding, inheriting strong leading edges and contours…AMP-23R never added sharpness, a nasty ringing in the top octave, there wasn’t a lifeless midrange delivery, as it added more flow, more emotions, more weight and color to my music, without overdoing it too much.

There’s a longer vibration in the human voice, there are more nuances that I can pick-up so easily and more important than ever, it just relaxes me every time I push that play button. You can certainly tune it to your liking with different D/A converters, headphones and loudspeakers, but I think its genuine sound should be experienced first and foremost with your current setup. There’s a world-class transparency, an absurd high level of detail retrieval that removed traces of mud in some of my planar-magnetic headphones (Audeze LCD-4 is a very good example) and some of the best layering and depth I’ve experienced with solid-state amplifiers. Pair it with a software defined FPGA DAC or with a mood-lifting R-2R ladder DAC and invisible threads will be pushing you closer to your nirvana, creating an intoxicating flow and easiness that is hard to describe by mere words.

We have a small cult-following around here for Hifiman Susvara and some of my friends that are driving their units with integrated, power or over-powerful headphone amplifiers came for a listen and I clearly remember their surprised faces and wide smiles. Past week-ends were quite busy, everybody was asking from where that flow, control and crazy dynamics were coming from. It fully drove the Suzy and made them sing the way we didn’t experience before on solid-state amplifiers.

Its midrange delivery was something truly special and it wasn’t about how bold or defined it was, but more about its feel and energy that was oozing from those guitars, violins and human voices. I still find it linear, honest and extended in the frequency response, but it didn’t charm me with its technicalities, but with the listening experience itself. It knows how to awake emotions in your tunes, how to be gentle and smooth, it also knows how to increase and decrease dynamics in split seconds. When it’s called for, bass becomes athletic and naughty, slamming as if two power amplifiers were bridged together.

This is my first experience with Enleum and it had a profound impact on the way I’m looking at solid-state amplifiers. It’s unlike any other unit that passed through my hands and if you can overlook its limited power output, I don’t believe it can get any better than this.

II. Noise floor in a stereo & headphone setup

This is one of the most powerful headphone amplifiers I know of and you shouldn’t get it for the sole purpose of driving sensitive loads as IEMs or portable over-ear headphones, it wasn’t really made for them. If you do have a substantial collection of portable cans and IEMs, may I suggest using a portable DAP, USB or Bluetooth dongle for a better compatibility, but if you’re brave enough, you can certainly do that with the AMP-23R too. I’m powering my audiophile setups with passive power conditioners from Plixir, BAC400 sits in my office powering my head-fi setup and BAC1500 in the living room, feeding two power amplifiers, a DAC and a streamer. Both weren’t made for cleaning up my power lines, as their job was preserving dynamics, so my tunes could sound the same at 5 P.M. as they do at 5 A.M.

Its common practice spotting background noises when overwhelming levels of power are being offered on tap, it’s the standard rule of thumb with analog amplifier designs. I’ve experienced this phenomenon multiple times in stereo and headphone setups and there are plenty of examples to give. Usually, transistor-based amplifiers aren’t the cleanest sounding units out there, especially the ones that aren’t using negative feedback, like this puppy right here. Obviously, not all amplifiers are made the same, as with a careful selection of components and great engineering skills, you can make an exception to that rule. When it comes to traditional Class-AB or Class-A amplifiers, none of them were completely noiseless with IEMs, not even top-tier units as Ferrum OOR, Burson Soloist 3X GT or Flux Lab Acoustics Volot.

Knowing that speaker terminals are glued together to its headphone jack, I prepared myself for some hiss passing by. I’ve engaged its low-gain setting, lowered its volume and commenced listening through a sensitive pair of IEMs and those were the FiiO FH9. I’ve unplugged them and plugged them back and checked again if the amp was turned on, as I couldn’t spot a rise of the noise floor. I wasn’t expecting an absolute silence with or without music playing in the background, but AMP-23R performed above my expectations even with such ultra-sensitive loads. My usual listening level would sit at around 9 O’clock, where (again) I couldn’t detect traces of noise or gremlins playing in the background. I’ve paused my music and went higher on that wheel and at around 12 O’clock some hum made its appearance felt, going louder as I was turning the volume higher. If I would hit play at that volume, I would become a deaf philosopher or maybe a literary critic for the rest of my days. Nobody could listen to music at those levels, meaning that Enleum’s amp is still an outstanding proposition for IEMs users around the globe. A few words of advice first: never use its high-gain setting with IEMs or portable over-ear headphones. I’m not worrying about noise floor, which naturally would sit higher, but about the drivers of your IEMs that might fry in microseconds. AMP-23R pushes absurd amounts of power on high-gain, something that was reserved only for Susvara, HE-6 or Abyss AB-1266 users.

I’ve unplugged it, run back to the living room and redid my tests in my stereo, but this time around I completely bypassed the Plixir BAC1500, powering it directly from the wall. I’ve got the KEF’s Reference 3 a year ago not only because I enjoy them greatly, but also ‘cause these are really good at sniffing out noise levels coming from integrated and power amplifiers. About half of integrated amps that I’ve tested to this day slipped some residual noises. Their UNI-Q mid-woofer and tweeter sandwiched together are extremely sensitive to source and amplifier noise and I have tens of examples that didn’t pass this test with flying colors. Luckily, there was no residual noise whatsoever, as Reference 3 sounded delicate as I know them to be on my AHB2 power amplifiers. There was a change in tonal balance, as AMP-23R added a heavier timbre, some liquidity and a higher midrange presence that was missing on Benchmark Media amplifiers.

III. Power Output

In my university and master years, I latched to everything that had numbers in it, be it math, accounting or statistics. Numbers always made sense to me, putting faith into them. When writing about numbers…Enleum’s unit will never impress when putting it against over-powerful amplifiers, especially if you bridge some of them like I did with two Benchmark AHB2 that can provide up to 380 Watts of power in 8 Ohms. AMP-23R will not impress a hardcore headphone enthusiast either, as on paper 4-Watts in 60 Ohms should drive most headphones out there, but certainly not all of them.

Most of the headphone and power amps that are surrounding me are more powerful to it, providing a higher headroom for difficult loads and yet when music started playing, Susvara came to life and brought a smile to my face, playing tunes in such a way that I didn’t expect in my wildest dreams. I must confess…when AMP-23R arrived at my front door, I didn’t bother unboxing it for a few days, as its specs weren’t where I wanted them to be.

After playing around with different amplifiers and coming back to AMP-23R, it was clear that power is not always made the same. For unknown reasons, 4 Watts felt more powerful to units that could provide double or even triple the power, how was that even possible?

A. Working as a Headphone Amplifier

How on Midgard a unit like this can fully drive the notorious Susvara at 12 O’clock position (half its power output) so loud, incredibly impactful and alive that other, more powerful units couldn’t do even at 1 or 2 O’clock position? Sensitivity plays a key role when choosing the right amplifier, raw numbers are still important and yet, Enleum’s amp felt more powerful to its declared numbers, so much so that I could use only two planar-magnetic headphones on its high-gain position and those were the Audeze LCD-4 and Hifiman Susvara. Everything else were begging for low-gain, so I would have a wider play on its volume wheel.

Simply put, AMP-23R is one of the nicest solid-state headphone amplifiers I’ve experienced in a very long time and it’s certainly one of the most powerful too. As you can imagine, everything like portable over-ears, IEMs and desktop dynamic headphones were easily driven on low-gain and I was rarely going past its 11 O’clock position. The biggest majority of my headphones are planar-magnetics, since I always admired their wall of sound and it didn’t have the slightest problem driving them all. Even Audeze LCD-5, Kennerton Rognir, Erzetich Phobos V2021 and Hifiman HE1000SE were driven with flying colors, with plenty of authority in the bass, sweetness in the midrange and with a harsh-free top octave. AMP-23R exhibited stronger dynamics to its competitors, it pounded my eardrums harder, sending my earlobes into a flip-flap fiesta. In the end, I’ve got an immaculate transient response and not even for a second, I felt that more power was necessary, leaving tons of headroom for higher dynamic peaks.

When Hifiman Susvara hopped on my head, I already knew what’s going to follow, as for about a week I’m listening to this exact configuration. When it comes to solid-state amplifiers, AMP-23R made a perfect match with Susvara, improving everything I love about them. AMP-23R was in the same league as driving them with two Benchmark AHB2 power amplifiers. I’ve got the same engagement factor, the same bottomless bass performance, the same iron grip over their drivers, but this time around a little more soul and emotion was pouring from my music. There was more energy building up in the midrange and I’ve got the most impressive treble delivery – crystal clear and defined and yet brightness free. Long story short, if you’re searching for an ultimate and no-compromise solid-state amplifier for your Hifiman Susvara, this is The One! In the latest chapters of this review, I will be comparing it with top-grade headphone amplifiers, please keep a watchful eye for that.

B. Working as an Integrated Amplifier

My KEF Reference 3 aren’t that easy to drive (86 dB sensitivity), as there were several units that entered clipping territory, even the ones that had two to three times more power on tap. On rare occasions a single Benchmark AHB2 was entering its protection mode (clipping LEDs blinking) with DSD and high-dynamic range content. My wife is glued to a bed for the next ~two months and I kindly asked if she is willing to listen to some tunes together. I’ve got a green light and we sat down for a longer listening session. A minute didn’t pass and I was asked what happened as Norah Jones sounded sweeter and livelier. Then Rodrigo y Gabriela stole our attention with snappier sounding guitars, then Nirvana’s MTV Unplugged confused us with sounds coming from the corners of the room, a clear sign that we’re dealing with a different tonality to Benchmark’s AHB2.

I could raise the volume up to 12 O’clock and sometimes it could be a little too loud for our apartment. The biggest surprise wasn’t the power remaining on tap, but the bass output and the amount of control that was felt while driving the Reference 3. Everything was exactly at their right places, bass notes were impactful and alive, midrange never felt dry or uninvolving, on the contrary…it was denser than ever before and their aluminum UNI-Q drivers weren’t scratching our ears with treble-intensive music, a thing I could never solve with affordable Class-D amplifiers. Challenge Accepted! I’ve said and engaged higher dynamic range tracks. Volume went up to 2 O’clock and there was still enough headroom remaining on tap. More importantly, I was still getting the same, highly engaging sound that invited for more tunes to be added to the playlist. No matter how hard I’ve tried, I couldn’t choke it down. I couldn’t make my windows dance to the rhythm of the music and my neighbors weren’t knocking at my front door, but do we really need ear-deafening levels in a flat? I can safely say that AMP-23R exceeded my expectations both as a headphone amplifier and as an integrated amplifier, so much so…that I’m contemplating in getting one too.

IV. Transient Response

Thor almighty, I finally arrived at my favorite chapter and what a chapter…When I’m looking at this tiny unit, the last thing that comes to my mind is an exquisite transient response and thunderous impact in the lowest octaves. Seriously now, can you believe a four-kilo amplifier could sustain bass lines, scary organ pipes, or deliver a serious punch in the chest? Usually, bass notes are coming to the surface with the help of big and scarry looking amplifiers.

Soo In’s secret sauce proved so effective at delivering fast AND impactful bass notes, that all other amplifiers near it…were lacking nerve and a nasty attitude. Don’t get me wrong, Ferrum’s OOR plus Hypsos and Burson’s Soloist GT were still powerful and mighty impressive, but never on the same page with Enleum’s fearless bass delivery. Its bass wasn’t overdone or elevated from linearity…but there was more energy dwelling down there waiting to be explored. AMP-23R gave a new meaning to everything that’s remotely close to bass, as even regular blues and jazz felt invigorated and meaner sounding. What I’m trying to convey is that, I don’t recall experiencing such an impressive transient response coming from a solid-state amplifier. When using it as a headphone amplifier, it’s almost too fun at times. Dynamics were unstoppable with this one, connect a mellow sounding headphone and watch those drivers fly and unleash their fullest potential. All my headphones felt radically changed, even my co-designed Apos Caspian felt clearer and more impactful sounding. AMP-23R never felt out of breath and it wasn’t running out of steam, more like on the opposite pole, leaving its competitors in the dust. These are some strong words, but it warms my heart knowing that a little transient response monster could do all this, without robbing too much space from my office. Try doing that with a Flux Labs Acoustic Volot or Trafomatic Primavera that occupies half of my work space.

A single question remained unanswered: Does the little one knows how to rock…hard? When Back in Black by AC/DC (Qobuz / Tidal) appeared on my playlist, for some reason I felt with a wheel in my hands pressing the accelerate, brake, accelerate and brake again in an endless loop. I couldn’t stop from head-banging, toe-tapping and feeling on top of the mountain, like in the good ol’ days of my youth. I’m back in black Aaaahhhh-Yeaaaaahhhh felt so raw, so bloated with mind-numbing stupidity, yet so mean and satisfying at the same time. While having oversimplified drums, three-note guitar notes mixed for 7-year-olds, its groovy nature stuck in my head for the rest of the day. This isn’t the Apex of rock music by any stretch of imagination, but it was a blast and an enjoyable listen throughout AMP-23R. Rocking hard indeed! When it comes to transients, pace, rhythm and timing, AMP-23R claimed the iron throne as the no.1 unit in my ranks.

V. Resolution & Transparency

Nowadays, top-tier resolution can be obtained even from affordable amplifiers thanks to noise-shaping techniques that THX-AAA (feed-forward) and NFCA (nested-feedback) amplifier modules put on the table a few years ago. There are tens of examples by now, starting with Topping’s A90 ($500) that was uber detailed and completely noiseless, followed by SMSL’s SP400 ($560) and finishing with the best one - Benchmark’s HPA4 ($3000) that could be spotted in a good deal of reviews around here. However, when applying such techniques, a chain reaction would happen on a deeper level…as if music’s aura was completely removed. Many people already moved to traditional Class-A or Class-AB amplifiers (me included) for this reason alone, as music wasn’t dwelling in such units. I’ve recently parted ways with the Benchmark’s HPA4, as to my ears units like Burson Soloist 3X GT and Ferrum OOR + Hypsos were bringing back that mantra, that feeling of epicness while listening to music. Transparency, as all other technicalities are extremely important, but if one can’t feel the music anymore…what’s the point in listening to it?

Units like Flux Lab Acoustics Volot, Ferrum OOR and Burson Soloist GT proved that a higher transparency can be obtained from transistor-based amplifiers, but deeper pockets would be needed for that to happen. All three units exhibited high-levels of detail retrieval, so much so, that Benchmark’s HPA4 didn’t feel in a league of its own anymore.

It so happens that Enleum’s AMP-23R is using some of the best transistors in existence and those are EXICON Mosfets. I have already experienced those exact Mosfets in three distinct devices and I can vouch for their detailed-oriented nature, while retained the soul of the music as much as possible. Secondly (and most importantly), Enleum’s newly developed Ensense Circuit employs zero negative feedback, featuring an ultra-fast and ultra-wide frequency response…Aha! There’s no feedback at all! That’s why the sound felt pure without messing with harmonics.

After some extensive A-B comparisons with the help of some of my closest friends, we came to a conclusion that AMP-23R is currently the cleanest and most transparent sounding solid-state amplifier that crossed our ways, followed by Burson’s Soloist GT, Flux’s Volot and then by Ferrum’s OOR. The funny thing? There’s a bigger difference between it and second-best amp, than between the second and third places. AMP-23R improved the leading edges so much, that some of my headphones were radically transformed into nicer sounding headphones. The best example I can give is Audeze’s LCD-4. I love these ones…these are my second-best headphones and I don’t like them for their (lack of) technicalities, I love ’em for their organic tonality that always uplifts my mood. LCD-4 are hoping on my head when I want to relax and have a great time when a brand-new album drops on Qobuz or Tidal. Hifiman Susvara on the other hand are my weapons of choice when I need to look at my equipment with a magnifying glass. AMP-23R removed that muddy and slow nature of LCD-4, while boosting their speed, leading edge and ultimately detail retrieval, as if I was listening to a mid-gen leap LCD-4.5. The same story repeated itself with many other units, Kennerton’s Rognir were bringing forward additional nuances that were missing on previously mentioned amplifiers.

Listening to Stardust by Hot Club of San Francisco (Qobuz / Tidal), hearing and (more importantly) feeling double bass notes, a violin and two rhythm guitars playing in the background felt so…real to me, as if Django Reinhardt himself raised from the grave and played for one last time. I didn’t need to stress myself hearing its intricacies even with a pair Audeze LCD-4 on my head. I see these guys reincarnating gypsy-jazz style, adding life with innovative arrangements, giving a new shape and inspiration to this long-forgotten genre. This is probably the craziest gypsy-jazz I’ve heard in a very long time and I can’t tell you enough how clean, pure and free from obstacles everything sounded on AMP-23R. When I’m Happy Just to Dance with You started playing, I felt how musician’s fingers were touching and sliding over guitar strings, such a small but satisfying detail was brought to the surface.

VI. Soundstage & Depth

Gone are the days when for a big & enveloping sound, you needed behemoth amplifiers like Audio-GD’s Master-9, AMB’s Beta-22, oversized integrated or power amplifiers. Burson’s Soloist 3X GT and Ferrum’s OOR are living testaments to that, as both units were able to untangle my tunes, place musical notes on individual shelves, without the need of tubes or over-engineered output stages.

Enleum’s amp does not rely on complicated circuity, more like on the opposite side with its simplicity and short signal path. Look closer at those Ensence modules and JET2 bias that were developed for a high-efficiency, add a formation of OMRON analog relays that are present in world’s best amplifiers and you’ll be getting the sound of AMP-23R. From inception until the final release, AMP-23R was designed as a simple, but no-compromise amplifier that wouldn’t stay in the way of signal’s purity.

AMP-23R surprised me one last time with its ability to deliver excellent imaging, placing the notes around me as if I’m no longer listening to open-back headphones, but to a well-thought near-field stereo setup. The beautiful intricacies weren’t lost in transit, as AMP-23R fully unfolded them for me, placing them at precise distances from each other. While this is not a balanced input to output amplifier, against all odds it opened up the windows towards music, pushing and pulling the notes around me as if a beefier amplifier was sitting on my table. I wish there would be a con to which I can latch on and write a longer chapter, but it simply refused to sound closed-in and personal even with crowded and overly mastered music.

Take Moon River by James Taylor (Qobuz / Tidal) as a very good example. His harmonica buried deep in the mix felt so outlined, leading the way for the rest of the sounds. His voice was passing by gently in the room, never interplaying with the rest of the instruments. A guitar to my left and another one to my right felt as different entities, as if someone added them later into the mix. There was an exuberant amount of air circling around that slowly remade a stereo track into a sort of binaural recording. Please try it out for yourself and experience one of the nicest layering and instrument placement that can be had with acoustic music. My former THX and NFCA amplifiers would place everything in a two-dimensional sound field, but right now…everything felt bigger, fuller and wider on all axes.

Besides an unshackled sound that flies in all directions, filling every gap in the room with nuance, it placed sounds at mismatched distances, so much so that several musicians felt closer and others went backwards a few steps, burying them deeper into the mix. Reconstructing depth information was always a difficult task with solid-state amplifiers, something that hybrid or vacuum tube amplifiers were doing so effortlessly. In the end, I’ve got an outstanding soundstage and depth for a solid-state amp and there’s nothing more to add in here.

VII. Frequency Response

A. Bass

Mentioning its incredibly clean, fast and impactful bass performance it’s like mentioning that all sugars are sweet, those things should be clear by now. Contrary to its weight class and size, AMP-23R carried a fuller-bodied, heavier-duty and denser type bass, standing out immediately from the first minutes. It indeed felt highly energetic, bolder and punchier sounding compared to first-class headphone amplifiers that were sitting near it. I didn’t expect it to be so powerful and impactful down low. I refused to believe it could awake sub-bass notes with my Reference 3 and while I’ve heard them as alive and hard hitting before, it happened only with mono amplifiers used in bridge mode. Starting with the lowest octaves and finishing with upper bass notes, AMP-23R had a perfect blend of impact, sustain and control. Could you really wish for more from such a cute little amp? The low-end is undoubtedly the hardest frequency to move, sustain and decay naturally and this is where it was shining brighter to its competitors. If you love your bass plumpy and substantial, then it got you fully covered. This isn’t a bass-heavy amplifier, as I’m still getting a linear bass performance, but the sheer impact and kick needs to be heard to be believed. The funny thing is that I started spotting bass-notes where I never believed I can find them, especially in a headphone setup where room acoustics aren’t a limiting factor.

B. Midrange

Its midrange delivery felt pure as a mountain spring. It was so refreshing, invigorating and life-giving. From decades of experience with integrated amplifiers, I counted a maximum of three to four amplifiers that delivered an organic, unrestrained and pure sounding midrange. This is one of its strongest abilities, as more substance was slowly bonding with my tunes. Vocals were simply crawling under my skin, as there wasn’t a hardness to them whatsoever, creating a foundation for an emotional performance and carrying the song forward. This part of the frequency response reached a whole new level of greatness and I don’t think that you’ll be missing hefty mids or punchy bass lines with an amplifier like this. Enleum’s amp sits on the opposite pole to a Benchmark AHB2 ($3000) and to all class-D amplifiers that passed through my hands. There wasn’t even a trace of dryness or thinness…as everything that appeared on my playlist was soul-touching, putting me instantly into a relaxed state of mind. There was definitely a higher midrange presence, as my tunes felt saturated, like boosting contrast on a high-resolution picture. It’s going to sound great for just about every genre out there thanks to its sweeter midrange section to the usual solid-state amplifiers.

C. Treble

Unlocking world-class imaging, providing precise spatial cues, pushing everything around are the jobs of your loudspeakers and amplifiers that are driving them. The key ingredients for that to happen are signal’s purity and a strong equilibrium of the frequency response. Elevate something in there and something else wouldn’t shine as bright. Even if it adds a higher contrast, brighter and crisper images, this is still a neutrally tuned amplifier and you should expect for a clean, straight and defined treble delivery. I’m getting prominent and well-defined trebles with boosted clarity, but without the usual letdowns as brightness or listening fatigue. This unit does remind me about world-class hybrid amplifiers as Trafomatic Primavera, that have a similar treble performance, which I find exquisitely clean and defined, yet velvety smooth and easy going. AMP-23R was so radical sounding in this department, that I couldn’t make it bright sounding…no matter how hard I’ve tried. Be it Hifiman HE1000SE, Erzetich Phobos V2021 or Audeze LCD-5, I couldn’t make it hot sounding in here as it was going through my treble intensive tracks as slicing butter with a sharp knife, it was so satisfying.

VIII. Comparisons

AMP-23R is currently the most expensive headphone and integrated amplifier that was tested around here and as such, I’ll be comparing it only with top-tier headphone amplifiers that passed through our hands.

Enleum AMP-23R ($6250) VS Ferrum OOR + HYPSOS ($3190) VS Burson Soloist 3X GT ($2799 with Super Charger 5A)

If you’re a manufacturer and my words are going to offend you in some way, then please accept my apologies, but understand that I need to stay true and honest to my readers and viewers. My opinions are always my own and that isn’t going to change anytime soon. I’ll be as objective as possible, without taking into account my personal preference. If you’re an avid reader, please enjoy the showdown.

All my comparisons are done in the morning, after a hot shower, two poofs of Audispray, a hot coffee and after volume matching them at 90dB with a decibel meter. All these things are mandatory, as I know that my hearing and mood would be at its prime.

  1. Enleum’s unique casework, ease of use and simplicity can’t be denied, it has the thickest metal plates all around it and the smallest footprint too, hence scoring top points when it comes to build quality. Sometimes I’m just starring at those bright Ferrum logos, but especially at Hypsos display when dynamics are going crazy. In split seconds it can go from 8 to 16 Watts, especially when Susvara hops of my head. I still find OOR and Hypsos unique looking and cleverly designed, Soloist GT comes as impressive and neat, it just doesn’t stand out as much to the rest.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 9.5
    • Burson Soloist 3X GT: 9
  2. When it comes to features, Enleum’s amp takes the lead as we’re talking about a top-tier headphone and integrated amplifier. This thing will drive all your diaphragms coming in different sizes and forms. Soloist 3X GT comes next as besides a three-way Crossfeed circuit for a speaker-like experience, there’s a fully-fledged preamplifier, two sets of XLR and RCA inputs (so helpful when doing comparisons), a subwoofer output and you can even use your headphones with a subwoofer if you will. Even if it comes feature packed to its teeth, Ferrum stack comes last. Hypsos lets you connect it to almost any DC powered audio component and OOR can also work as a preamplifier.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 9
    • Burson Soloist 3X GT: 9.5
  3. When it comes to sheer power numbers, since I’m trying to compare apples to apples here, I’ve recalculated their power ratings in 60 Ohms and it seem that Ferrum stack offers around ~8 Watts in 60 Ohms, Soloist GT provides about ~6 Watts and AMP-23R lags behind with its 4 Watts in the same impedance. However, when Hifiman Susvara started its show, I didn’t feel that either or these were lacking oomph and dynamics…on the contrary, AMP-23R felt a little more powerful since I barely arrived at its 12 O’clock position. Nonetheless, I will be ranking them according to their power ratings
    • Enleum AMP-23R: 8.5
    • Ferrum OOR & Hypsos: 10
    • Burson Soloist 3X GT: 9
  4. When it comes to natural timbres, I believe that right now, AMP-23R is one of the most impressive solid-state amplifiers to date. It really sounds more like a top-tier hybrid amplifier, there’s lushness, liquidity, tactility, plus you can’t beat its dynamic range. Its bass and midrange delivery were second to none, hence scoring the highest points. Ferrum’s stack does very well too and if I would never try the Enleum, I would be a happy camper with the OOR and Hypsos. I still find the OOR mighty impressive, it’s that Enleum is slightly better in every possible way. Soloist 3X GT sounds more like a traditional Class-A amplifier, going with a reference tuning, choosing not to interfere as much with the frequency response. Compared to the rest, GT adds a sprinkle of treble energy and for treble heads it would be a little more impressive. My reference headphones already have world-class transparency and treble information and that slight treble boost might harm their tonal balance.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 9
    • Burson Soloist 3X GT: 8.5
  5. Moving on to soundstage, layering and depth information, Enleum’s zero negative feedback proved more holographic sounding, resembling (again) the sound of a well-made hybrid amplifier. There were more spatial cues, wider spaces between each and every note and its layering was to die for in both a headphone and stereo setup. Soloist GT was by a hair smaller sounding, narrowing the overall picture, but it still pushed everything outside my head, never messing with open-back headphones. Ferrum OOR came third, as it couldn’t portray a massive scale with orchestral work and it couldn’t provide the same depth information that was coming from the rest. OOR was good in here, just not on the same level.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 8
    • Burson Soloist 3X GT: 9
  6. Moving on to transients and dynamics, contrary to its power rating, Enleum’s creation was bringing the thunder every time some nasty electronica would appear on my playlist. It wasn’t even a contest, there was a lightning-fast delivery, an instant decay of the notes and a ruthless impact with the right tunes. I don’t recall Audeze LCD-5 bringing forth so much bass information, but the true star of the show were LCD-4…I couldn’t stop from head-banging with them on my head. Ferrum OOR came next, it was still pushing and pulling those diaphragms like a berserk, there was still impressive dynamics with all my headphones, but it wasn’t as fearless and naughty sounding to me. Burson’s amp went down by a notch compared to the rest, hence scoring a little lower.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 9.5
    • Burson Soloist 3X GT: 9
  7. I left the hardest test for last, as when it comes to transparency and detail retrieval, all of them were highly resolute. Still, after closing my eyes and trying a few reference tracks, AMP-23R felt a little clearer sounding, there weren’t traces of grain or muddiness that sometimes might appear on Ferrum OOR. AMP-23R went ahead of the pack and delivered a clearer overall presentation, Soloist 3X GT came second and I still believe it’s the cleanest Class-A amplifier I’ve tried to this day. Ferrum’s stack came third, as it wasn’t as impressive, lacking sharp contours and precise leading edges. With OOR, some tunes were gentler, appearing in a rounded manner, like a smoothing filter was applied all over my music.
    • Enleum AMP-23R: 10
    • Ferrum OOR & Hypsos: 8.5
    • Burson Soloist 3X GT: 9.5
  8. Final Results
    • Enleum AMP-23R: 68.5 points
    • Ferrum OOR & Hypsos: 63.5 points
    • Burson Soloist 3X GT: 63.5 points

All tests didn’t take into consideration their price points, but their ratings are somehow reflecting the critical hits your wallet might suffer. AMP-23R is one of the most expensive solid-state headphone amplifiers to date and for a good measure, as I couldn’t find flaws with this one. It’s mighty technical and incredibly punchy sounding. I’m on the sixth day of writing this review, as once music starts playing, I’m forgetting that I need to write a few notes down. It really pushes me closer to my music, trying to impress with the act of music listening, reminding that there’s still some life in your headphones / loudspeakers that wasn’t known before. It’s bass and midrange needs to be heard to be believed, I won’t forget its dynamic swings anytime soon. When it comes to timbre, Ferrum stack comes incredibly close, I find it almost as engaging, alive and impactful, but there’s less transparency and less air is traveling around. A few notes are still lurking in the shadows, but everything is never pushed above my shoulder level. Lastly, Soloist 3X GT provides that traditional Class-A sound that is effortless, powerful, explosive and dynamic, but it’s slight bump in the treble could steer off a few headphiles. Soloist GT impressed with its immaculate transparency and big picture, as even closed-back headphones (Kennerton Rognir) refused to sound inside my head. I find the Ferrum stack and Soloist GT equally impressive, just different…

No matter from what angle I’m looking at, AMP-23R stood out as a better sounding unit, wining top points on 6 out of 7 tests and proving that specs aren’t always that important.

Conclusions

I’ve heard plenty of great sounding solid-state amplifiers by now, but none of them were crawling under my skin as soon as music started doing its mojo. Its different working principle was felt immediately. My tunes were revitalized, freed from any limitations, transients were riding a roller-coaster as if a (much) bigger amplifier was pushing and pulling them around. It freed my music from all traces of hardness, brightness and muddiness, a trick that solid-state amplifiers didn’t master as of yet. Live recordings felt incredibly transparent, energized and fresh, that often times I would just stop, take it from the table, have a good look and wave a finger at it. It connected me to my tunes in ways that only hybrid or full-tube amplifiers were capable of doing, without bringing forth their obvious drawbacks as a higher weight, size, power consumption and heat dissipation. Nothing is nearly perfect around here, but with AMP-23R on my table, I was looking for a needle in a massive haystack. I can only complain about is its limited power output, apart from that, prepare a pillow on your chest and a lengthy playlist as you’re in for a ride…for a joy ride.

It outperformed current production solid-state headphone amplifiers by a long shot and that was mirrored in its price tag. For countless of reasons, it didn’t feel as an ordinary headphone / integrated amplifier and that’s why Enleum’s nerdy team deserved our highest praise and award! Congratulations to the team and we’re looking forward to their next doings.

Being at the top of the crop would cost you a pretty penny, more exactly $6250 (that includes anti-vibration feet). You can get it directly from their online store right here or you can contact your local Enleum distributor right here.

Do I think it’s expensive? Yep. Do I think it’s worth it? Totally!

PROS:

  • A beautifully crafted device
  • Rock-solid build quality, its small footprint is a chef’s kiss
  • Fully drove a pair of KEF Reference 3 with aplomb
  • Fully drove a wall-of-headphones, including the notorious Hifiman Susvara
  • Sounds tactile, always trying to connect with your music
  • Effortless, unrestrained and completely free
  • Lacks grain, hardness or muddiness of any kind
  • Transparency and cleanness in its purest form
  • Spacious, open and wide sounding, fully preserving depth information
  • Authoritative sounding, slams and pounds like a (much) bigger unit
  • Outstanding diaphragm control, an instant start and stop of the drivers
  • The best dynamics I’ve experienced via headphones
  • Great tonal balance, tries to be organic and life-like sounding
  • A no-compromises two-in-one unit
  • If you’re searching for the best solid-state Susvara amplifier – This Is It.

CONS:

  • Unfriendly with your wallet
  • Not the most powerful integrated

ASSOCIATED EQUIPMENT:

  • DACs: Denafrips Terminator Plus, Rockna Wavelight, Audiobyte HydraVox & HydraZap, Gold Note DS-10 Plus & PSU-10 EVO, SMSL VMV D2, Singxer SDA-6 PRO, FiiO K9 PRO ESS, Gustard X18,
  • DAPs: Hiby RS6, FiiO M17, M11 Plus ESS, Shanling M8
  • Headphone Amps: Enleum AMP-23R, Ferrum OOR + Hypsos, Flux Lab Acoustics Volot, Burson Audio Soloist 3X GT, Trafomatic Primavera, several Topping, SMSL & Gustard units
  • Preamps: Musician Monoceros
  • Integrated Amps: Enleum AMP-23R, Burson Timekeeper 3i
  • Power Amps: Benchmark AHB2 (x2)
  • IEMs: FiiO FH9, FH7, FA9, FA7S, FD7, Meze Rai Penta, LittleDot Cu KIS, Kinera Skuld, 7Hz Timeless & others
  • Portable headphones: Sony WH1000-XM4, Sennheiser Momentum 2, Meze 99 Classics
  • Full-sized headphones: Hifiman Susvara, HE1000SE, Arya Stealth, Audeze LCD-5, LCD-4, Erzetich Phobos V2021, Phobos V2018, Erzetich Mania, Kennerton Rognir, Magni, Gjallarhorn, Vali, M12S, Apos Caspian, Sendy Peacock, Apollo, Aiva & others
  • Loudspeakers: KEF Reference 3, Sound Of Eden Crescendo UNO
  • Interconnects: QED Reference (x2), Topping TCX1 (x2)
  • Speaker cables: Kimber PR8, Audioquest Type4
  • Power Cables: Isotek EVO3 Premier (x3), iFi Audio SupaNova (x2)
  • Balanced Isolation Power Conditioners: PLiXiR Elite BAC1500 (stereo setup), Elite BAC400 (headphone setup)

Overall score 95/100

Value/Features 94/100
Power Output 93/100
Resolution 95/100
Dynamics 96/100
Frequency Response 95/100
Stage Size 94/100
Build Quality 95/100
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