Overall Score: 91/100

Ferrum Audio ERCO Review

My Video Review:

A group of mad scientists banded together in 2020, starting spreading a new type of virus that was putting goose bumps all over their victims, butterflies in their poor stomachs, intensifying their heartbeats, while mercifully hitting their eardrums. What a nasty type of virus! That renegade band was later revealed as Ferrum Audio, proudly lead by the bright minded Marcin Hamerla into the enemy lines. We’ve been infected by that virus a few months ago, that opened a Pandora’s Box for us. Jokes aside, Ferrum’s second born OOR altered our preconceptions, as finally a desktop-friendly headphone amplifier could drive the most demanding headphones with an incredible ease, doubling down on dynamics and quadrupling enjoyment factor in the process. It didn’t sound like any other headphone amp we received up to that point, hence appearing later in so many posts around here.

Before posting the OOR’s review, we’ve been told that another product is in the works, that didn’t have a name at that time. An all-in-one unit that was merging together a highly sophisticated DAC, a powerful headphone amplifier and an active preamplifier in a similar box to that of the OOR. Hell Yeah! We were anxious in trying it out and three days later, an early version was already fluttering our ears. A few months passed and the unknown unit was later revealed to be their ERCO all-in-one combo.

Did you know that you can pick Esperanto language from Google Translate list? Esperanto is a constructed international auxiliary language created by a Warsaw-based L.L. Zamenhof in 1887, which is used even today. In Esperanto ERCO goes for ‘ore’, in Latin FERRUM goes for ‘iron’, in Dutch OOR goes for ‘ear’ and I hope their next product would be called GÅSEHUD, for obvious reasons.

Hundreds of discrete components that can be found in OOR, made their way into ERCO, there’s a unique DAC section which I will be describing in a minute, a modified version of OOR’s headphone amplifier section and finally, an active preamplifier section instead of the usual digital attenuator found on most DACs of today. ERCO wants to be remembered as a compact & no-compromise unit that didn’t abide by the rules. It goes for €2395 and you can enhance its performance by getting a much nicer HYPSOS power supply for an extra €1195. ERCO with and without the HYPSOS will be tested with a bunch of IEMs, high-impedance dynamic and low-sensitivity planar-magnetic headphones and its story has just begun.

Unboxing Experience

There’s one thing that Ferrum didn’t change a single bit to their former champions and that’s their packaging. As usual, ERCO arrived double-boxed with a lot of hardened foam for a better protection during shipping. In usual Ferrum fashion, there’s an impressively detailed Quick Start Guide that will explain down to the smallest details all its inputs, outputs and use cases. Inside the box, you’ll find the unit itself, a 60-watt Meanwell switching mode power supply, a power cable and a USB Type-C cable. Although ERCO can be used as a dedicated preamplifier in a stereo gig, it was designed mainly for a (desktop) near-field environment, hence lacking a remote control. You won’t find a user manual in there, which should save a few trees in the long run, in case you need it, you can download it from here.

Design & Build Quality

I’ll get straight to the point: ERCO looks, feels and smells exactly like a Ferrum product from a mile away. You can easily mistake it for their OOR, as it has similar design cues, only a slight rearrangement of its front panel and a busier layout on its back. Everything else looks exactly the same and that’s a good thing, as I always liked that sleek and minimalist look of their OOR and HYPSOS. While we’re looking at an oversimplified metallic brick, I still enjoy its minimalist look and understated color scheme that has a tremendous WAF attached to it. I still dig that bravely illuminated Ferrum logo, you can increase or decrease the light output and if it bothers you in late night listening sessions, you can turn it off completely. As it was the case with OOR, its top plate was drilled with hundreds of tiny holes that will move hot air away from its electronics, prolonging its service life. It gets mildly warm after few minutes of use and I’m recommending leaving it in a well-ventilated area. You can stack it atop a Ferrum HYPSOS power supply, I used this configuration for the most part of this review and I had no issues with heat dissipation. With all that said, please avoid putting hotter units on top and make sure you’ll never block its ventilation holes.

Its industrial look isn’t attracting a lot of eyes, but when HYPSOS goes underneath it, they will surely attract some. I still hope Ferrum can update the HYPSOS with a digital VU-meter, instead of the usual current and power output gauges, that would be classy and cool. Its front plate has a thickness of around 4mm, it’s thick enough and you can be sure that external wireless interference wouldn’t pose a problem.

You’re getting a big volume knob that provides a higher resistance (a huge plus for me), input and gain switches are next and then a pair of 4.4mm balanced and 6.35mm single-ended headphone jacks for a double visual impact. I’m a little sad that the 4-pin XLR jack of the OOR was dropped, but that’s alright as the 4.4mm Pentaconn jack still has an adequate surface area without wobbling in the socket, as it usually happens with 2.5mm balanced connections. You won’t find a single button on its front plate, nor ugly screws, its switches have a firm click, which suggests that we’re dealing with a high-quality product. Compared to its competitors as Burson Conductor 3X GT and Flux Lab Acoustics FCN-10, ERCO offers a smaller footprint, so you can easily integrate it into a tidy looking desktop setup. With a net weight of 1.8 kilos or around ~4 lbs., I find it lightweight and easy to maneuver around my desk.

The same tall rubber feet are located underneath that will absorb all sorts of shocks and tiny vibrations coming from within its electronics, making it work at an optimum performance. These are bolted and if you fancy nicer looking shoes, you can always swap them with Viablue QTC spikes that are matching its matte-black case. Those will elevate it higher, for a better ventilation and badass look.

Controls & Connectivity

You can power it with its external switching mode power supply or with a much nicer HYPSOS hybrid power supply, that was specifically tailored to be used with OOR and ERCO. HYPSOS will land another blow to your wallet, but it will skyrocket ERCO’s performance to new heights and if you need only the best, HYPSOS looks a must-have upgrade down the road. After selecting a digital or analog input, ERCO will power on. If you’ll be using it with HYPSOS, then you can control the incoming voltage from 22V to 30V, that will be slightly altering its voicing and sound signature. HYPSOS shows useful information in real time as how much power and current are being delivered to your headphones and the working voltage of the ERCO.

ERCO employs a high-performance DAC, headphone amplifier and a dedicated line stage, it’s a fully balanced one and that’s why a 4.4mm Pentaconn and a 6.35mm headphone jacks are located on its front panel.

Taking a glance on its back-panel, from left to right there’s a pair of XLR and RCA analog outputs to be used as a DAC only or as a DAC and preamp combo. A pair of RCA analog inputs follows, meaning that ERCO can be used as a dedicated preamplifier if you please. Three digital inputs are next as Optical, Coaxial and USB Type-C that will unlock its internal DAC section. You can find a bypass rotary switch that will disable its volume pot, making it work as a fixed-voltage DAC. Be warned: in this case you shouldn’t use a power amplifier, as it will blast full power towards your speakers, that could potentially damage their drivers or badly affect your hearing. Below it, there is another pot that will control the brightness of the Ferrum logo, you can also turn it off completely. Lastly, there’s a Ferrum Power Link 4-pole DC input that connects directly to the Hypsos and an additional 2.5/5.5mm DC input that lets you connect its default Meanwell switching mode power supply.

Under the hood of ERCO

First of all, there’s a high-performance and fully balanced DAC section used in current mode operation for the best results. ERCO is also a fully balanced and powerful headphone amplifier that could drive even the most demanding loads and lastly, it’s an active preamplifier to be used in between your source and power amplifier or all of the above combined into a neat looking case. The ERCO project is well known to me, as I believe I’ve tried an early version a few months ago, in return for precious feedback to the Ferrum team. The digital domain is extremely interesting to me and it was the right thing guiding them in making a splash with their first DAC/Amp combo. Although it might looks like their first digital-to-analog converter, I can assure you that the people behind Ferrum crafted a dozen of DACs under a different logo. Make no mistake, Ferrum is very much into digital audio for at least two decades now.

What I like the most about ERCO is that it doesn’t look like a regular DAC/Amp combo on the inside. Although it uses a few op-amps in the signal path, there are so many discrete components that will be leaving a positive mark on its overall performance. This isn’t your copy/paste DAC/Amp/Preamp combo that hopes for the best. Starting with its DAC section, I can spot a single ES9028 PRO DAC chip of ESS-Technologies, which is their second-best silicon to date. This particular chip can work in mono, stereo or 8-channel mode with either current-mode or voltage-mode operation. The biggest majority are using it in a stereo config with a voltage mode operation, due to a (much) lower cost, research and development time. However, if you want the absolute best performance, this silicon gives a higher SNR if current mode is being used. This configuration adds a lot to the cost, as a powerful I/V (current to voltage) conversion stage needs to be built around the DAC chip. Luckily, I’m spotting a custom I/V conversion stage made from a combination of op-amps and discrete devices.

The second most important thing in a DAC is timing and that’s why a 100 MHz clock generator is almost glued together to the DAC chip for the shortest possible signal path. Two high-precision crystal clocks are located nearby for standard, double or quadruple and octuple sample rates of 44.1 or 48 kHz and another clock for DSD material.

An XMOS XU216 digital receiver will take care of the USB input and an old-school Burr-Brown receiver will take care of the AES and S/PDIF inputs. ERCO can still unfold and fully decode MQA files and for that, an ARM Micro-controller (MCU) will be giving a serious helping hand.

Its headphone amplifier section is fully balanced and I again see a combination of discrete components plus a LT120 current feedback operational amplifier per channel that can output up to 1.1 Amperes. There are four headphone amplifier circuits, suggesting that we’re dealing with a fully balanced drive. ERCO pumps 6.1 juicy Watts in 50 Ω and 1.2 Watts in 300 Ω via its 4.4mm balanced output and about ~4 times less via its single-ended output, which should be more than enough for the biggest majority of headphones.

Its preamplifier section is not the usual digital attenuator that most DAC manufacturers are using and I’m seeing again a hybrid stage consisting of several op-amps and discrete components. Even if it has only RCA inputs on its back, ERCO up-converts the signal into a balanced one with an active stage, followed by a gain and attenuation circuit that happens in analog domain (Thanks Odin!). Yes, that’s an audio-grade ALPS Blue Velvet volume pot that you can find in most amps and DACs of today. It isn’t known for a perfect channel balance, but thanks to high-precision analog relays, the signal remains perfectly balanced in between both channels even at the lowest and highest volumes.

Lastly, about a third of its PCB is occupied by a power supply and filtering stage, that looks similar to that of the OOR, which mind you, never increased the noise floor with sensitive IEMs. Its internal PS still preserves the double input and output filtering, including independent power rails for both channels.

Long story short, you are looking at a unique looking DAC, headphone amp and preamp with a different internal layout, that should leave a mark on the sound quality. Ferrum was never about making similar sounding products and that was felt immediately after trying their creations.

Test Equipment

Ferrum ERCO looks like a statement all-in-one unit and that’s why I decided testing it with my entire headphone collection. I will be testing its noise floor with ultra-sensitive IEMs, I’ll move to portable over-ears and lastly, all sorts of desktop headphones will be hopping on my head, ranging from affordable dynamics to high-end planar-magnetics.

I will be testing it with and without the HYPSOS hybrid power supply that should unlock the maximum potential of this unit and in some of the latest parts of this review I’ll be driving the hardest headphone I have in my stable: the notorious Hifiman Susvara.

Alright folks, my body and ears are ready for some music, so let’s hit some eardrums!

Sound Performance

I. Preliminary Impressions

Before starting a long listening session, I need to double check that ERCO was set to high-gain, that 4.4mm output was being used and that I still had some ice in my gin-tonic. If it wasn’t clear from the start that a different design philosophy was used behind it and if you are still wondering if it has anything in common with the usual ESS-Sabre converters or is it going for absolutely linearity, focusing on sharp leading edges. Au contraire mon frère, as I’m getting a very different picture, an old school vibe to be more precise, similar to 80-ties music that saw an emergence of the superstar style, putting a bigger accent on the midrange delivery and bass definition, while slashing parts of the upper treble for an enjoyable listen in the long run. I’m getting a fuller bodied and a darker overall tonality that puts a bigger accent of the emotional side of music listening, instead of a dead-flat and ultra-linear presentation and you know what? I deeply appreciate a change of pace.

Ferrum were always honest about their unique approach in dealing with electronics, calling their OOR as the only amplifier with a soul and I can clearly see that ERCO goes with a similar design philosophy. It didn’t remind a single bit about the usual ESS-Sabre converters that I’m testing on monthly basis. I have a thing with DACs as you already know, these creatures always fascinated me thanks to their complicated nature. I’m trying to stay well-informed about every corner of HiFi, especially when it comes to D/A converters. Coming close to forty ESS-Sabre based converters tested in a headphone and stereo setup, I know how these digital creatures are making their entrance felt on the podium. While some of them had distinct features, their sound signatures were often times very similar. Still, a tiny squad was going against all odds, trying to re-write the bad reputation that ESS silicon gathered across the years, by sounding bigger and deeper, by getting harmonics right, by tingling my ears with a fuller bodied sound, while dropping remaining traces of sharpness.

ERCO is certainly part of that group and if you’re already checked my OOR and HYPSOS review, then it goes without saying that ERCO goes with a similar tuning, dropping a little bit of power to its older brother, but getting a really nice DAC section instead. Even without the HYPSOS in place, ERCO was trying to show me the beautiful side of the music, completely discarding listening fatigue, thinness and remaining brightness for good. If you’ll be using the 4.4mm jack – which I wholeheartedly recommend, then you can almost forget about running out of steam. Got some high-impedance Sennheiser and Beyerdynamic headphones or low-sensitivity planar-magnetics? Don’t you worry as it got you covered, providing a lot of power, headroom, speed and dynamics that a headphone enthusiast could crave about.

This is not your usual op-amp based DAC and headphone amplifier, as a lot of discrete components are still laying around, leaving a positive mark on its presentation. Sharpness was traded with liquidity, linearity with a fun and engaging sound signature and a flat frequency response was swapped with a warmer sounding one that adds a bit of color and saturation.

II. Adding the Ferrum HYPSOS into the mix

HYPSOS is not your usual transformer-based power supply, but more like a hybrid power supply that uses a switching mode power supply in the first stage that will clean up the mess and a linear transformer later on for a better current delivery. Hybrid power supplies are on the rise as of late, I started seeing them in a lot of units of today, from Gold Note PSU-10 EVO, to Musician Aquarius and Denafrips Gaia and many others embraced a hybrid power supply design.

Before telling you about the HYPSOS and what it brought to the table, first you need to know about the improvements to the electrical grid that I’ve did a few years ago. When we moved to this apartment, the first thing I did was replacing every single wire from the wall, with thicker OFC copper wire of a higher purity. The entire electrical grid was replaced with a new one and I made sure that my office would use a dedicated power line that wouldn’t interfere with the rest of the house. I used an even thicker copper wire in my office and two separated fuses, one for my PC and peripherals and another one for my audio chain. Although costly as hell, it improved my listening experience…but still, at night my music was somehow livelier sounding. Soon after I’ve added a Plixir Elite BAC400 passive power conditioner in my personal audio setup and a bigger Elite BAC1500 in my stereo and you guessed it! Music became alive in daylight as it was in late night listening sessions.

Since I wanted to have a higher impact of the HYPSOS, I completely removed my passive power conditioners, connecting ERCO and HYPSOS directly to the wall. With or without the HYPSOS, ERCO wasn’t increasing or decreasing the noise floor, suggesting that its internal power supply is already good enough, keeping the noise at bay. HYPSOS didn’t make the background blacker, but I have felt my tunes complete, flowing more naturally in a way. ERCO is already quite a warm sounding unit, but HYPSOS was nicely binding the notes together. There was a better flow with all my tunes, a continuity in the movement of the notes instead of a micro stuttering that was happening with ERCO alone. If you ever heard a really well-made reel-to-reel tape player, then HYPSOS was reminding a little about that sound, adding some of that magic into the mix. Instead of harder and stiffer notes, HYPSOS were transforming them into water, moving them softly around the room via speakers and gently around my head via headphones. There was another, smaller change with high dynamic range tracks. When Los Angeles Philharmonic or Minnesota Orchestra started playing, I’ve felt more air pushed forward when big drums were being hit. It was already impressive on the ERCO alone, but with HYPSOS I was jumping around, getting an instant power delivery on the spot and a higher SPL in nano-seconds. HYPSOS didn’t only add a substantial amount of flow, but improved dynamics that were better tingling my ears with high resolution tracks. I’ve felt an improved low-end delivery and a higher presence of the low-intensity notes.

The difference with and without the HYPSOS in place was actually bigger compared to their their OOR, mostly because there’s a DAC section too, which is more sensitive to a cleaner and stabler power intake. I’m well aware that ERCO will inflict a critical hit to your wallet and maybe it’s better leaving the HYPSOS for a well-deserved Christmas present later on?

III. Noise Floor

ERCO performs similarly to their OOR, that uses a related power supply and filtering stage, getting a strong feeling that I’ve listened to this unit already. Pulling power from a 60-Watt power supply isn’t a challenging task, when most of the PCB is populated with a lot of discrete components, but doing that without raising the noise floor? That’s the big challenge that audio engineers are facing when making amplifiers of all sorts. Amp builders are playing a hide and seek game with the noise floor for almost a century now, trying to move it out of band (above our hearing abilities), by moving quantization errors in a feedback loop (functioning as a filter), by involving an appropriate amount of dither or negative feedback, trying to bury the noise as deep as possible.

Without confusing you with unknown terms, I went directly on its 4.4mm jack and high-gain and it seems that increasing or lowering the volume didn’t impact the noise floor a single bit. There was indeed a gentle hiss playing in the background on its high and mid-gain position with the most sensitive IEMs I have in my possession, but it wasn’t as high, as it was on Burson made amplifiers. Naturally, its low-gain position cleaned up the noise and I could finally enjoy ultra-sensitive IEMs as FiiO’s FA9. It wasn’t completely dead-silent, as when I detached and attached the IEMs back, a gentle white noise could be felt playing in the background, but it was so faint, I could ignore it completely if I wanted.

When music started playing, there is no way I could spot it anymore and in the end, I believe ERCO works just fine with either on my IEMs. When I moved to regular IEMs (read: lower sensitivity ones), then I could no longer hear the White Wolf howling in the background (any Witcher fans around here?). As you can expect, any other portable over-ear or desktop headphone performed noiseless, including sensitive headphones as Focal and Kennerton ones.

I redid my tests in a stereo setup, using it as a DAC and preamplifier, controlling a pair of Benchmark AHB2 power amplifiers (one per speaker) which drove a pair of KEF Reference 3 speakers. My personal noise sniffers are the UNI-Q driver arrays of the Reference 3, which were capable of debunking so many amplifiers by now. Luckily, Reference 3 weren’t pushing the noise forward, even when standing still in their vicinity and that makes me quite happy. My speaker’s transparency didn’t take a hit, their speedy and impactful presentation remained intact and I’m glad that ERCO could easily replace a dedicated DAC and preamp in a well-made stereo setup. Those exact tweeters were picking up the noise with less than perfect DACs and preamps, but luckily that didn’t happen with the ERCO. My biggest gripe is that I needed to run back and forth a few times as ERCO lacks a remote control.

IV. Power Output

Ferrum ERCO has a similar case dimensions and weight with their outstanding OOR amplifier, but since we’re dealing with a DAC and headphone amplifier combo, there was less space reserved for its amplifier section, hence getting a little less power on tap. From 8 Watts per channel on OOR, it dropped to 6.1 Watts, which in practice didn’t alter its personality and driving power that much, with the exception of a single headphone.

We are still looking at one of the most powerful DAC/Amp combos ever to be released and it can easily be compared with bigger and scarier beasts. With most of my headphones, I felt like it was over 9000 power wise, always leaving plenty of headroom, especially on its high-gain and 4.4mm Pentaconn jack. Starting with sensitive dynamic headphones and finishing with difficult planar-magnetics, it didn’t have a slightest problem driving them all, including difficult loads as the Audeze LCD-5, LCD-4, Erzetich Phobos V2021, Kennerton Rognir (planar) and Sennheiser HD800S. Rarely I was going past its 12 O’clock position as there was a substantial headroom remaining on tap for crazier and wilder dynamic swings. Dynamics were scaling up accordingly, it was reaching their peaks, while tightly controlled their drivers.

Since I was getting a clean and a distortion free bass, while preserving oomph and rumble, it was clear to me that ERCO was driving well said headphones and getting their tonalities right. It was elevating the bass and midrange output by a little bit, which had a beneficial effect on several headphones as Erzetich Phobos V2021, Sennheiser HD800S and Kennerton Rognir, hiding just a small portion of their omnipresent treble delivery.

It offered a fuller bodied sound to the usual dead-neutral NFCA and THX-AAA amplifiers, while gently adding more soul and emotions into half-century old recordings. Bright tilted headphones worked amazingly well, slashing a substantial amount of glare and remodeling their sound signature little by little. Hifiman spawns, I’m looking at you.

With Hifiman Susvara I was already preparing myself for a similar performance to what I was getting from OOR – which sits highly in my personal amp rankings, easily in the top 3 best solid-state headphone amplifiers that I ever tried. This time around high-gain was mandatory form the start, I was again getting decent dynamics and above average bass performance, suggestion that ERCO was still far from giving his last breath. What was 2 o’clock on the OOR, moved to 4 o’clock on the ERCO and I was prepared going a bit louder for a similar SPL versus the OOR. With a little bit of sadness, it seems that ERCO isn’t doing justice to the Susvara as OOR was doing so easily and bravely. Dynamics weren’t as jumpy; soundstage took a serious hit and I wasn’t able to transpose into my audiophile Nirvana. It was doing an okay job, a better one to say a Benchmark HPA4, but still, Susvara was far from being well driven.

I was getting a lower SPL ‘n headroom and shier dynamics in the process…but only with the Hifiman Susvara. It felt like ERCO was providing less current, as I wasn’t getting that tight, grippy, punchy and speedy presentation of the OOR, otherwise Susvara worked decently enough. It won’t do Susvara and Abyss AB-1266 TC justice as OOR would do with a huge grin on its metallic face and that shouldn’t come as a surprise to anyone. If you already own a high-performance DAC, then maybe OOR should be on your short list of headamps to be auditioned in the future. With all that said, if you’re a self-proclaimed minimalist and low sensitivity headphones are not on your daily audiophile diet, then ERCO will replace a well-made DAC and headphone amplifier and still deliver a ton of joyful moments.

V. Transient Response

First and foremost, never use its single ended output as the difference between SE and BAL is substantial and I’m not about sheer power numbers, I’m about old-fashioned dynamics. Disregarding the Hifiman Susvara, ERCO always appeared to me quite speedy and highly energetic sounding with modern tunes, but it was even crazier via that 4.4mm jack. Another improvement was felt when HYPSOS came out to play with it. Nothing wrong with its bundled SMPS, but HYPSOS was adding more oomph and rumble in the lowest octaves, weight and substance to an already high-quality bass delivery.

In its stock form, ERCO will be providing quick shift in dynamics and an instant start and stop of the drivers at the cost of a lighter weight bass delivery. For example, Audeze LCD-4 and Kennerton Rognir are the only bass canon headphones of my collection that are hopping on my head once experimental electronica stuff starts playing. These can sustain longer bass notes and bring the thunder when asked for. These are impressive sounding with lightning-fast tunes, always getting me the full force of the low-end. If I was getting an ultimate performance out of their OOR, I’ve got a 90 out of 100 bass rumble and punch with the ERCO. Adding the HYPSOS would bring it to around 95 points, but still, OOR was a little better, providing more of everything in terms of dynamics, sitting undefeated on its iron throne.

ERCO is a mighty fine sounding unit and at its price point it will certainly get the job done, but if you want all and everything, including strong kicks with electronica tunes, then I fear you’ll need to get higher priced separate devices. ERCO has a powerful family resemblance, I could feel the Ferrum genes passing through its circuit board, but it was a little calmer and gentler sounding to its bad-intentioned brother.

When Boys Don’t Cry by The Cure (Qobuz / Tidal) started grooving behind my ears, a pair of drum sticks jumped into my hands and a double pedal setup emerged below my feet, going for a wild drum solo ride for the rest of the track. More than 40 years later after its initial release, this bass-heavy groovy tune still encourages men in showing their emotions. ERCO’s crystal-clear playback was separating bass and drums so well, as if a large patch of silence was sitting in the center, sounding alive and punchy for its whole duration. Along with neat production touches like the clattering trash-can percussion that echoes into the distance, the empty spaces between the notes highlighted the group’s dynamic variations. Every drawn breath, each guitar tone snapped into the darkness, falling distinctly and significantly. ERCO was insistent enough to make me dance to my own jitters (yes, I’m doing that quite often), making a bold statement that impressive dynamics are still flowing through its silver-plated veins.

VI. Soundstage & Depth

ESS-Sabre based converters aren’t known to be pushing the boundaries, delivering an out of head experience via headphones, but such limitations could be bypassed with clever engineering skills. A fully balanced signal path, starting with the D/A conversion stage and finishing with the headphone amplifier section, a shedload of power sitting under that hood, seasoning everything with discrete components can mean a few things once music starts playing: prepare your imagination and zooming skills, as you’ll be surrounded by music played on different tonalities, you’ll be enveloped by layers and sub-layers of sounds, circling around you head. Perfect measuring headphone amplifiers that carry THX-AAA and NFCA tech were always two-dimensional and flat sounding to me, but that isn’t the case with the ERCO, that pushed my tunes far and wide, as if I swapped my display with a bigger one.

The perception of a breathable sound versus to my stereo rig wasn’t that obvious, due to the nature of headphone listening itself, but still…the whole experience felt holographic, never locking musical notes inside my head, I felt at peace and relaxed, as it pushed that energy around my body. Even tiny IEMs started sounding decompressed compared to portable USB dongles and portable DAPs, even if tiny drivers were sitting centimeters away from my eardrums.

ERCO has an actual line-amplifier circuit built-in and I felt that when it was driving a pair of Benchmark AHB2 power amplifiers. It sounded more spacious and completely effortless compared to the usual ESS Sabre DACs. Although great sounding when used as DAC only units, Topping D90SE, Gustard X18, SMSL DO200 and D1SE felt smaller, shier and less holographic compared to the ERCO. The Polish wonder box wasn’t only spacious and deeper sounding, but also grain free, improving the transient response and ultimately, driver control of my loudspeakers. I can only imagine the positive vibes people will get to experience with their ERCO in a nearfield desktop setup, while powering active monitors.

When Baba Yaga by Minnesota Orchestra Showcase conducted by Eiji Oue (Qobuz / Tidal) recorded and mixed by Reference Recordings started playing, I stopped whatever I was doing, taking a six-minute pause, as ERCO was painting a massive scale, widening it to my left and right, but also above and below my head, even with a pair of closed-back Kennerton Rognir. Sennheiser HD800S were sitting near me waiting for their turn, but I didn’t flinch, slowly inhaling and exhaling air with my eyes closed shut. There was a substantial amount of air traveling around the notes and I could almost feel a huge dome above the auditorium, with notes flying far away, decaying so slowly and gently. This is not your regular cozy sized acoustically treated room and somehow that was transposed immediately.

VII. Detail Retrieval & Transparency

In the initial design phase of the ERCO, there was one goal that stood out from the rest: making it as transparent as possible, without making it harsh or fatiguing in long listening sessions. After making a custom current to voltage (I/V) conversion stage and a headphone amplifier with a ton of discrete components, made everything ever freer and clearer sounding as well. Its hybrid output stage was preserving that clean and uber-detailed nature of the ESS-Sabre silicon, while making everything vivid and alive. It seems that Ferrum finely polished it in the later stages of its development, making it clearer and more open sounding in the process.

When it comes to chip-based converters, you still can’t outperform a good ESS-Sabre PRO implementation and ERCO is a resident proof to that. Living for a few years with ‘instrument grade’ DACs and headphone amplifiers, I feel that ERCO isn’t going with the same ultra-revealing and overly sharp presentation. While I never felt that ERCO was sugar coating my music as lower-grade R-2R ladder DACs were doing by default, it was trying to stay true and honest, without boosting their leading edges. In a direct comparison, a FiiO K9 PRO would appear clearer and more detailed on the first listen, but ultimately drier and sharper later on.

A highly detailed source can be sometimes tiresome in long sessions, especially when there’s some digital glare associated with the unit, but luckily, ERCO doesn’t have any of that. It felt fuller bodied and considerably weightier to the usual Delta-Sigma converters that are passing thought my hands, at the cost of less impressive leading edges.

Two days ago, I was listening to Twilight by Neil Young (Qobuz / Tidal) and at the 2 minute and 4 second mark I’m getting this low-intensity buzz that sounds very much like our door buzzer, so I’m standing and opening the door, realizing that nobody was standing in there. I’m going back to my office and voila! I’m hear that buzz again! What’s more interesting is that I know this album and this track so well and yet, I don’t remember hearing that sound so distracting. While I’m not huge Young fan, I’m always coming back to this album as it always impresses me with its cleanness, depth and layering all around. It sounds great on my stereo and legendary via headphones. That velvety sax, those powerful drum hits and the haunting lines are always putting me into a Zen state. There’s a strong balance between technicalities and musicality and I can certainly attribute similar words to the little ERCO that was playing tunes on repeat for more than two weeks now.

VIII. Frequency Response

A. Bass

ERCO goes with a textured and weighty bass delivery. It wasn’t as deep reaching, nor as fearless and impactful sounding as their OOR was mated with a world-class DAC, but it’s very similar in all regards. There is none of that lightweight and ethereal bass performance of entry to mid-level DAC/Amp combos, which directly elevates it higher, closer to some of the nicest all-in-one combos. While I’m getting less bass quantity wise, I’m still dealing with a clean, multi-layered and distortion-less bass delivery. In all honesty, I listened mostly to electronica and rock tunes on this one, as I couldn’t get enough of that warmish bass and dense midrange delivery. Both the Audeze LCD-4 and Kennerton Rognir injected a healthy dose of dopamine, even lower-quality tunes felt boosted with positive vibes. This is a funky sounding unit in all regards and if you’re after clean and punchy bass lines without overdoing them too much, I think ERCO will be right up your alley.

B. Midrange

ESS Sabre PRO silicon and midrange should probably never used in the same sentence, but Ferrum’s young talent proved that miracles can still happen. There is absolutely nothing of that boring, thin and lifeless performance that I’m getting with entry level Sabre DACs. Expect a stronger and a colorful midrange, that feels a little boosted compared to the rest of the spectrum. Even headphones as Sennheiser HD800S changed their personality, getting more warmth and midrange density compared to a FiiO K9 PRO or Burson Conductor 3X GT. There is still a long road ahead versus top-of-the-line units, but I feel that ERCO’s midrange is so close to them. There’s an added weight latched to masculine voices and a longer vibration of string-based instruments, making guitars and violins so emotional sounding. it does midrange very well and I wish more ESS-Sabre converts would choose a similar path, embracing midrange purity and naturalness above anything else.

C. Treble

ERCO’s treble performance was going against the rules and usual patterns. There was plenty of definition, detail and shimmer, but none of that fake treble ringing of the fully-loaded op-amp based converters. It seems that Ferrum nicely balanced its tonality, getting everything right without dropping or rising portions of the frequency response. I’m way past that point when bright equals highly detailed and even if ERCO didn’t feel as extended and ultra-revealing past top-octave, in some ways I actually enjoyed a change of pace, as I could go a little louder with bright tilted headphones on treble-intensive tracks. My lengthy rock playlist went down my throat in no time and I was already craving for me, a sign a loud cymbals, punchy snares and zingy bells never bothered me. A nasty treble ringing is sometimes associated with ultra-linear THX-AAA and NFCA amplifiers, but that was nowhere to the spotted in here. I find it more life-like and easy going, I can even listen to Hifiman Sundara and Arya Stealth all day long and that wouldn’t be an issue at the end of the day. Overall, Ferrum’s ERCO just might be one of the most natural sounding combos I’ve experienced as of late.

My Conclusion

My admiration for Ferrum’s ERCO started after opening its hood and seeing a different layout and design philosophy to the usual DAC/Amps combos, that are trying to keep the cost down as much as possible. While being small and lightweight, its masters went with top-grade components that wouldn’t limit its uplifting abilities. Just look at those hundreds of discrete components and big number of analog relays used for a perfect channel balance. Its MCU unlocked MQA playback on every possible digital input, even it’s single-ended analog input is later up-converted into a balanced one! There are indeed a few op-amps in its signal path, but at the same time ERCO doesn’t cost you and arm and a leg, nor does it occupy half of your working space.

Ferrum fully preserved the soul of the music, the warmth it’s definitely there, an open and wide soundstage didn’t run away, its frequency response felt complete and perfectly balanced and the only thing that was missing the fun was listening fatigue.

I still find it easy to like, its feature packed alright, it offers a great selection of inputs and outputs, an industrial design reminiscent of their OOR and HYPSOS and a high-quality craftsmanship throughout. While it might look expensive with its €2.395 price tag, it is only by €400 costlier to their amp only OOR, offering an outstanding value in return.

I liked everything about it, except its limited headroom and shy dynamics with the Hifiman Susvara, hence scoring a well-deserved Silver Award!

You can get it from their online store right here and in case you are getting one, please leave a comment below. I’m curious to know how it works with your headphone or near-field stereo setup.


  • Minimalist industrial design
  • Rock-solid build quality & small footprint
  • A feature packed 3-in-1 unit, great I/O options
  • Great tonal balance, leaning towards an organic sound signature
  • Full-bodied, lush and smooth sounding for the most part
  • Open and wide soundstage, excellent imaging
  • Extended frequency response at both ends
  • Noiseless performance via Low-gain, equality impressive in a stereo setup
  • Lacks any forms or brightness & treble glare
  • Clean and detailed sounding, without adding an over-sharpness filter
  • Powerful headphone amplifier section, could drive most headphones out there
  • Funky and engaging sounding at all times


  • HYPSOS looks like a must-have upgrade later on
  • Can’t drive the lowest-sensitivity headphones that well
  • Lacks a remote control to be used as a preamp in a stereo setup


  • DACs: Ferrum ERCO, Audiobyte HydraVox & HydraZap, Chord Electronics Dave, Gold Note DS-10 PLUS & PSU-10 EVO, Gustard R26 Discrete, Topping DX7 PRO+
  • DDCs: Musician Phoenix, Singxer SU-6
  • DAPs: FiiO M17, M11 Plus ESS, Shanling M8, M7, Hiby RS6
  • Headphone Amps: Ferrum ERCO, Ferrum OOR + HYPSOS, Trafomatic Head 2, Trafomatic Primavera, Enleum AMP-23R, Burson Soloist 3X GT, Flux Lab Acoustics Volot
  • Preamps: Musician Monoceros
  • Power Amps: Benchmark AHB2 (x2), Burson Timekeeper 3i
  • Loudspeakers: KEF Reference 3, Sound of Eden Crescendo UNO
  • IEMs: FiiO FH9, FA9, FH7, Meze Rai Penta, Rai Solo, LittleDot Cu KIS, Hiby Crystal 6, 7Hz Timeless, Kinera Skuld & others
  • Full-sized headphones: Hifiman Susvara, Hifiman HE1000SE, Sennheiser HD800S, Audeze LCD-5, LCD-4, Erzetich Phobos V2021, Phobos V2018, Erzetich Mania, Kennerton Rognir, Vali, Apos Caspian, Sendy Peacock, Apollo, HarmonicDyne Poseidon & others
  • Interconnects: QED Reference (x2), Topping TCX1 (x2)
  • USB Cables: Supra USB Excalibur (x2), Chord C-USB, Matrix Hi-Fi USB
  • HDMI Cables: Supra 8K HDMI 2.1 (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)

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