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Manufacturer: HEM
Price (when reviewed): 2395 €

Contact: Al. Jerozolimskie 475
05-800 Pruszków | POLSKA



Provided for test by: HEM


zdjęcia Ferrum | Wojciech Pacuła

No 214

March 1, 2022


FERRUM FERRUM is a Polish audio brand owned by HEM, one of the most experienced companies in this industry, which has been designing and manufacturing devices for MYTEK for 20 years. The first Ferrum product was the HYPSOS power supply. The second project is the OOR balanced headphone amplifier, and the third is the ERCO DAC, which we are testing as the FIRST MAGAZINE IN THE WORLD.

ESTABLISHED IN 2020, FERRUM was conceived as a proprietary brand of the HEM company. Let us remind you that at the same time the cooperation between HEM and the American company MYTEK was ending. MARCIN HAMERLA, the head of HEM, in an interview for our magazine in 2019, said that, from 2000, all Mytek products were made in Warsaw. What's more, apart from the AMP amplifier all of them were designed first by him, and then by a team of young engineers he formed (more HERE |PL|) .

The first product with the Ferrum logo that left the plant in Pruszków, where the company's headquarters is located, was a non-obvious product, the DC Hypsos power supply. We saw it by the end of 2020, and we tested it in the December issue of HF (see HERE). A non-obvious product, as I say, which however immediately gained recognition all over the world and became a point of reference in many editors offices of audio magazines; Let me remind you that the editors of our friend magazine bought several units for themselves, and the device received the STATEMENT in High Fidelity award (German Edition 2021; more HERE).

The Oor headphone amplifier, which was introduced in mid-2021, quickly became no less popular (more HERE). We liked this device so much that it received our BEST PRODUCT 2021 award. As it turns out, the third device that came out from the minds of HEM engineering team is the ERCO, a digital-to-analog converter combined with a headphone amplifier. And we would like to tell you about this product this time.

| A few simple words…

Owner, chief engineer

⸜ Engineers behind the ERCO: (from the left) Paweł Gorgoń – Head of R&D, Krzysztof Moshrif – Business Development Manager and Maksymilian Matuszak – Hardware Designer

AUTOMOTIVE FANS KNOW THE CONCEPT OF A CAR CHASSIS. It is the most expensive and mechanically complicated structural element of a car, to which all the "organs" of a car are assembled to in the production process. For this reason, the car chassis are built universally and later used in a variety of vehicles. The AD/DA converters play a similar role, in which the digital heart, the equivalent of the car's chassis, connects and controls all the converter modules, and its architecture determines the interconnectivity of the equipment as well as the boundaries and quality of the conversion (all emphasis - red .).

It sounds like a hell of a job? Yes, it is. And that's why it has to be a complex element. And that also means expensive because you really need to develop two different platforms, connected by an eternal node of architecture: hardware and software. For this reason, we develop a converter’s "car chassis" every few years. We developed the previous architecture in 2012-2015. Two Mytek converters, the Brooklyn ADC and the Brooklyn DAC, were a direct result of the work. This family was then joined by the Manhattan DAC II, Brooklyn DAC +, Liberty DAC and the Brooklyn Bridge.

But time passes and new is replaced by newer. We were very proud of the previous architecture as it was the most advanced project we had completed thus far. A very successful one, too. But PAWEŁ GORGOŃ, its father, is an ambitious and resourceful person. And even more than that: he is also very ambitious and even more inventive. In addition, he has learned a lot since 2015. New ideas were seething in his mind.

So I gave an order: "TORPEDO LOS!". All lovers of the best movie from World War II know what it means and the characteristic music "plays" in their heads ... So it started. Two years ago the missile went away and a few months ago it accelerated sharply going strait for the finish line. Erco's heart saw the light of day. New hardware, based on a smaller number of more advanced "chips". A software masterpiece that integrates all the necessary functionalities. Or maybe not a masterpiece, but a cymes? I can not make up my mind…

If the digital part is the heart of the converter, then its soul is the analog section. It is the source of the magic of audio equipment. You can create great digital algorithms, write great software, but without a good "analog" stage we could never charm the customers. The one who performed the sonic magic was MAKS MATUSZAK, our wunderkind, creator of the award-winning OOR.

The D/A conversion in the new converter is based on a very carefully "wired", battle-tested chip, the ES9028PRO. The balanced all way through analog circuit was designed by HEM's R&D department from scratch. Uncompromisingly. Our engineers discussed, re-prioritizing, painstakingly browsing catalogs for the new chips, and then experimenting with prototypes.

Erco features two headphone outputs, unbalanced and symmetrical - the latter in the Pentaconn 4.4 mm standard. The headphone amplifier module is built on the basis of ideas working so good for the Oor. Due to the limited size of the device, we could not transfer the Oor 1:1 to Erco - the combination of an amplifier with an output of more than 8 W, working in a modified AB class, and a D/A converter would mean too much power loss, which could not be passively dissipated from devices. Erco therefore has a lower output, with a sonic signature very similar to Oor.

And most importantly: Erco is pronounced with c, not k! Our foreign customers will certainly have serious problems with such pronunciation :)


ERCO IS A DIGITAL-TO-ANALOGUE CONVERTER. It is also a headphone amplifier. Both sections can be used independently or together. Its duality is best reflected by the inscription on the rear panel, also repeated on the PCB: "Headphone DAC". What's more, if we so wish, with a small switch on the back panel, we can connect the potentiometer to the output path for line sockets and control the volume, for example, of a power amplifier or active loudspeakers.

Ferrum offers three digital and one analog inputs, has an analog volume control stage for headphone amplifier and line outputs, and two headphone outputs - balanced and unbalanced; There are also two line outputs, also balanced (RCA) and unbalanced (XLR).

The device uses exactly the same chassis as the two previous devices from this company - Hypsos and Oor. It is small, measures 217.5 x 206.5 x 50 mm (W x H x D; without knob, feet and sockets), and weighs just under 2.8 kg. The housing is made of bent stainless steel powder-coated with black varnish, and the whole is placed on small rubber feet. It is in this part that the company logo, which is in fact a symbol of iron, was laser-cut, illuminated with white backlit. The intensity of the backlight can be adjusted using a small knob on the back of the device.

The front panel features a volume knob and two small switches. One selects gain level, the other selects an active input. There are three gain levels and four inputs available. In the middle position, the input selector knob has a "standby" position, so it also functions as a power switch. Turning on the device does not change the brightness of the backlight logo and the only indication that the power has been turned on are the LEDs visible through the cutouts in the housing. On the left there are two more headphone jacks - the classic "big jack" ø 6.35 mm and the balanced 2.5 mm jack.


„JACK” TYPE PLUGS AND SOCKETS are the most popular way to connect headphone amplifier/smartphone/computer and headphones to each other these days. This is one of the older types of connections, and its sources can be found in the SCRIBNER’S C.E patent. from 1874. He then patented a link he called the "jack-knife". It was a socket-plug pair, where the plug was a ø ¼ ”(6.35 mm) pin with two contact fields separated by a dielectric. Its structure has hardly changed to this day, except for the shape of the "hot" contact - instead of the round contact area we are dealing with a "mushroom-shaped” one.

A plug of this type is called a "big jack" because its smaller versions were also created: a "mini" 3.5 mm jack, mono and stereo, and even smaller, with a diameter of ø 2.5 mm, called " sub-mini ". "Jack" can feature two contact areas - signal and ground, three, four or even five. Each field has its own name:
• Tip (T),
• Ring (R),
• Sleeve (S).

So these plugs are often called TRS; the mono plug would be TS, and the stereo plug with a microphone connection (for example in smartphones) TRRS. The latest version of this plug is developed by Sony, the 4.4mm Pentaconn. 'Penta' stands for five, 'conn' is short for "connection", so it is a TRRRS plug. Its task is to carry a balanced signal (more about the Pentaconn plug HERE |PL|).

SYNCHRONIZATION of the Ferrum DAC with the input signal source is indicated by an orange LED. Unlike, for example, in the Mytek Brooklyn Bridge file player, there is no display or even a few LEDs indicating what signal and of which parameters is currently played./p>

Inputs are found on the rear panel - there are one analog and three digital ones: USB, optical Toslink and RCA. The USB input is unusual, because it features a USB-C socket. There is also an analog output, in two forms - on unbalanced RCA sockets and balanced XLRs. These sockets look solid, they are gold-plated and were probably provided by the Swiss Neutrik.

The device is powered by an external 24 V DC switching power supply, but it can be supplied with voltage up to 35 V DC. In the middle of the device there are additional filtering and voltage stabilizing systems. We can supply power either through a classic 2.5 mm plug, or - if we want to use the Hypsos power supply - through a very good WEiPU socket (Series 12), which features a bayonet latch.


⸤ HOW WE LISTENED The ERCO digital-to-analog converter was tested in the HIGH FIDELITY reference system and compared to the D/A section of the Ayon Audio CD-35 HF Edition SACD player, which also worked as a transport, as well as to the Mytek Brooklyn Bridge file player. As always, I was most interested in how the Polish DAC handles CDs, because in their case, like in a lens, the advantages and disadvantages of digital devices are concentrated.

The Ayon digital output was connected with the with the DAC’s input using RCA → RCA Acrolink Mexcel 7N-DA6100 II cable, and the DAC was powered with the Harmonix X-DC350M2R Improved-Version cable. I placed its power supply on two Acoustic Revive RCI-3 stands. Erco stood on the top shelf of the Finite Elemente Master Reference Pagode Edition Mk II rack on its own feet, and on its top I placed the Verictum X Block passive EMI / RFI filter. In my system I use RCA cables and this is how the Ferrum DAC was tested.

To evaluate the headphone amplifier, I used two pairs of planar headphones - HiFiMAN 1000 V2 and Audeze LCD-3 - and the dynamic Sennheiser HD800. The first and third of them use Forza AudioWorks Noir Hybrid HPC headphone cables. They were connected to the amplifier with an unbalanced cable with a 6.35 mm TRS plug from Furutech.

Recordings used in the test | a selection

⸜ MARIO SUZUKI, Masterpiece II: Touching Folklore Music, Master Music XRCD24-NT021, XRCD24 (2018)
⸜ DOMINIC MILLER, November, Q-rious Music, PRQRM 115-2, „Promotional Copy”, CD (2010)
⸜ STING, The dream of the blue turtles, A&M Records/Mobile Fidelity UDCD 528, Gold-CD (1985/1990).
⸜ JEAN-MICHEL JARRE, Magnetic Fields, Dreyfus Disques/Epic EPC 488138 2, CD (1981/1997).
⸜ KING CRIMSON, In The Court of the Crimson King (An Observation by King Crimson), Atlantic/WOWOW Entertainment [Japan] IEDG-01, 7” Platinum SHM-CD + DVD-Audio (1969/2016).
⸜ KING CRIMSON, In The Court of the King Crimson (An Observation by King Crimson). 50th Anniversary Box Set, Atlantic/WOWOW Entertainment [Japan] IEZP-128, „2019 Remix by Steven Wilson”, 3 x HQCD + BD Audio (1969/2019).

⸜ AQUAVOICE, Silence, Zoharum ZOHAR 168-2, Master CD-R (2018).
⸜ PRIYA DARSHINI, Periphery, Chesky Records JD446, Master CD-R (2020).
⸜ ROGER WATERS, Amused To Death, Columbia/Sony Music Labels (Japan) SICP-30785~6, BSCD2 + Blu-ray (1992/2015).
⸜ KRAFTWERK, THE MIX w: KRAFTWERK, 3-D The Catalogue, KlingKlang | Parlophone 95873424, 7 x CD (2017).
⸜ OSCAR PETERSON, Unmistakable, Sony Music/Zenph Studios 951702, „Zenph Re-Performance”, CD (2011).



LISTENING TO THE FIRST-IN-HISTORY DAC by Ferrum was an extremely comfortable experience. The music flowed freely and I was not disturbed by any anomalies or a "personality" of the device. It is concrete, not bland, it corrects the signal in its own way, of course. However, these adjustments are part of the whole, that is, they constitute something more than themselves. These are never things detached from the presentation.

Which was obvious already with the first album I listened to, the Masterpiece II: Touching Folklore Music, an album with three classical guitars, by MARIO SUZUKI. This album was recorded in one day, without overlays and corrections, straight onto a half-inch analog tape, and then subjected to the K2 mastering and released on the XRCD24 disc.

Its directness and honesty was presented by Erco without any modification. The sound was smooth, a bit warm, with a wide panorama, that is, the way I know it from playing it on more expensive devices. The leader's guitar located on the axis has been slightly zoomed in and enlarged. The Polish DAC does something like that, but also does not blur the differences in distances from other instruments located on the sides. It's just that the events on the axis are placed quite close to the line connecting the speakers.

It worked equally well with the DOMINIC MILLER’s acoustic guitar recorded on the November album. It had a brighter timbre, it is ultimately a different instrument from a classical guitar, but it was also recorded a bit higher, in a more polished way. I'm not saying it's bad, it just fits the concept of the whole album, where we also have electric guitar, drums, bass and keyboards. Simply switching from one record to another resulted in a different vibe. Which the DAC showed really nicely, without brightening the Miller's recording too much.

It was still smooth, fluid playing. But it was also clear that the Polish converter does not extend bass very low and that its sound is - after all - rather open and more "sparkling" than "dark". Perhaps the closest to the truth would be to say that this device is aimed at reproducing the midrange in the best possible way, but without warming it up and closing it in. So the Erco sounds in an incredibly pleasant, friendly way, without resorting to such measures as emphasizing the lower midrange or rounding off the attack of the treble.

Therefore, the cymbals from the Miller’s disc had a sonorous character, quick attack and long sustain. Their "substantiality", that is weight, was not as high as with the reference player. However, I did not count on it. But I was counting on honesty - and that's what I got. Erco is even better in this respect than the Mytek Brooklyn Bridge. The D/A section in Mytek is a bit more selective and resolving, but also less coherent. The differences are not very big, it seems that the Polish DAC is a development version of Brooklyn. But these are different devices and you can hear that Erco is simply a more sophisticated product.

This is why the reverb accompanying STING's vocal in the Moon Over Bourbon Street was long and clean, therefore the saxophone positioned very far in the mix was clear and was not enlarged. All this was in perfect harmony with each other, allowing for comfortable listening. Yes, the Sting double bass was smaller and did not have a strong foundation - this is one of the features of the tested DAC. If we are looking for a fleshy, low-reaching bass, we have to look elsewhere.

It does not mean, however, that the Erco sounds light, nor that it is not anchored to the bass base. Everything in its sound is arranged in such a way that it harmonizes with each other, so we are not even aware of the limitations of this device until we compare it with another one - a more expensive or simply with a different sound characteristics one. And there is also the character of low tones that we get from the Erco. And they are as smooth as the treble and just as pleasant.

Listened to at the end of listening sessions, JEAN-MICHEL JARRE from the Magnetic Fields from a CD remastered in 1997 by Scot Hull in Masterdisk studios in New York, sounded perfect, just perfect. There was also a dark treble - this is what this album sounds like - there was an emphasis on the midrange, there was also a lot of mass in the bass. The most important thing, however, was that all of this played together, I did not think about this or that aspect of the sound, and it was only the awareness that I am supposed to listen analytically, so that I could share my observations with you, that forced me to analyze it.

So I had a wide panorama - the tested DAC widens it a bit, so that the sound occupies the entire "wall" in front of us. It also had a nice low midrange and upper bass, delivered in a naturally soft and pleasant manner. The device does not blur the sound, it is rather precise than not, but it is also surprisingly "forgiving". So Jarre's album sounded full and I did not feel the need to search, change or switch anything. With its limitations, resulting from the price point adopted by the designers, it was a very nice, surprisingly refined sound.


CONTRARY TO THE D/A SECTION of the tested device, the headphone part has a quite distinct "own sound". Moreover, it won't work as well with a wide range of headphones. I clearly preferred the Audeze LCD-3 headphones over the HiFiMAN HE-1000 V2 headphones that I usually use. With the latter the sound was very clean and smooth, but too bright. I had an impression that Erco was not quite able to drive them.

On the other hand, with Audeze I got a dark, extremely atmospheric presentation, even though the sound differentiation was not particularly high. It is not a product that would allow you to clearly capture the differences in mastering. When I got used to it, it turned out that the device offers something else, something sought after by most music lovers: incredible ambiance.

The amplifier showed the spatial effects very well, both in the case of the recorded with the use of the Neumann KU-100 "artificial head" album by PRIYA DARSHINI entitled Periphery, and right after that on the studio-rendered surround space from the KRAFTWERK’S THE MIX, from the 3-D The Catalog box, ("Headphone Surround 3D | Special mix for standard headphones only”). It was quite a tube-like sound, without clear cymbals and long reverbs, with calmed down dynamics, but with tangible instruments and a great feeling of being in the middle of the events.


WHEN I WANT TO LISTEN TO THE KING CRIMSON’S In The Court of the Crimson King (An Observation by King Crimson) I most often use its 7” Platinum SHM-CD version released in 2016. I like it for the honesty of the sound and its internal coherence. Recently, however, I noticed that I have been listening more and more often to the new mix of this material, prepared by Brian Wilson, and released in 2019 in the In The Court of the King Crimson (An Observation by King Crimson). 50th Anniversary Box Set. There are three HQCDs and one BD in it, and the material was mastered using JVC's K2HD Mastering technique.

Listening to it with the Erco showed me why - it is simply a much more resolving sound and more coherent at the same time. The Polish DAC offers similar features. Its sound is incredibly friendly, and at the same time selective and clear. The presentation has a soft "underbelly" with it, and at the same time it is compact and full. The bass extension comes to an end at some point, but we probably won't even notice it. The instruments on the axis are pulled up closer and the edges of the panorama are expanded. These are its own characteristics.

However, it can convey the atmosphere of the recording in an unforced way. It offers a complete, organized presentation for relatively little money. It is also a very competent headphone amplifier, with a clear, transparent sound that can be tamed with the dark sound of the headphones. In a word - another extremely good, and at the same time the most versatile and "sound-friendly" Ferrum product.


ONE CAN MISTAKE FERRUM DEVICES with any others. Finding such a characteristic "something" that distinguishes a given company is extremely difficult and most often ends with a caricaturist, not original design. For Ferrum, this ”key" is a square corten element on which the company logo shines. This gives the whole character and distinguishes it from a gazillion of similar digital-to-analog converters.

As I said before, the device does not offer an extensive "user interface", and the only element that helps in operating it is the LED signaling the synchronization of the DAC with a digital signal source. The only convenience for headphones owners is the amplifier’s gain switch.

The entire interior is occupied by a single printed circuit board. The vast majority of components are SMD ones, except for the capacitors in the power supply section, relays (Omron) and a large, four-channel Alps attenuator. The signal from the S/PDIF inputs goes to the Burr-Brown DIX 41921 digital receiver, and from the USB directly to the ARM chip in which the algorithms allowing the conversion of the USB signal to "understandable" one for the converter are stored. You can see two clocks next to it, but the main clock is a very nice element located next to the D/A converter.

And it is the ESS Technology ESS9028PRO chip, widely used in audio, in various price ranges, for example in the LUMIN T2. It offers support for PCM signals up to 32 bits and 384 kHz and DSD up to DSD512. The chips is not new, it was developed in 2016, but it is still very popular due to its low cost and good parameters it offers. The Texas Instruments and Burr-Brown (OPA1632) integrated circuits work respectively in the I/V conversion section and the output buffer. In turn, the OP Amps by Linear Technology Corporation and - again - Burr-Brown are working on the output.

Although the ESS chip offers 32-bit digital volume control, the designers used an analog Alps attenuator instead. It turns out that the headphone amplifier section is not just an accessory, but an equal device. Large Linear Technology Corporation LT1210 circuits are used there, two per channel, in a balanced configuration. These are amplifiers with a large output current, working with current feedback, and capable of driving low impedance loads. As it turns out, the unbalanced output ("big jack") is not gold plated, but the balanced is.

The power supply used in the tested device is similar to those used by laptops - it is a SMTP device delivering 24 V DC. However, the converter can be powered up with voltage of up to 35 V DC. Inside the device there are additional filtering and voltage stabilizing circuits.

You can see that it is a product of an experienced company, and additionally of an "engineering" company - order, cleanliness of the system, but also interesting solutions.


Reference system 2021

1) Loudspeakers: HARBETH M40.1 |REVIEW|
2) Line preamplifier: AYON AUDIO Spheris III Linestage |REVIEW|
3) Super Audio CD Player: AYON AUDIO CD-35 HF Edition No. 01/50 |REVIEW|
4) Stands (loudspeakers): ACOUSTIC REVIVE (custom) |ABOUT|
5) Power amplifier: SOULUTION 710
6) Loudspeaker filter: SPEC REAL-SOUND PROCESSOR RSP-AZ9EX (prototype) |REVIEW|
7) Hi-Fi rack: FINITE ELEMENTE Pagode Edition |ABOUT|


Analog interconnect SACD Player - Line preamplifier: SILTECH Triple Crown (1 m) |ABOUT|
Analog interconnect Line preamplifier - Power amplifier: ACOUSTIC REVIVE RCA-1.0 Absolute-FM (1 m) |REVIEW|
Speaker cable: SILTECH Triple Crown (2.5 m) |ABOUT|

AC Power

Power cable | Mains Power Distribution Block - SACD Player: SILTECH Triple Crown
Power (2 m) |ARTICLE|
Power cable | Mains Power Distribution Block - Line preamplifier - ACOUSTIC REVIVE
Power Reference Triple-C (2 m) |REVIEW|
Power cable | Mains Power Distribution Block - Power amplifier - ACROLINK Mexcel 7N-PC9500 |ARTICLE|
Power cable | Power Receptacle - Mains Power Distribution Block: ACROLINK Mexcel 7N-PC9500 (2 m) |ARTICLE|
Power Receptacle: Acoustic Revive RTP-4eu ULTIMATE |REVIEW|
Anti-vibration platform under Acoustic Revive RTP-4eu ULTIMATE: Asura QUALITY RECOVERY SYSTEM Level 1 |REVIEW|
Power Supply Conditioner: Acoustic Revive RPC-1 |REVIEW|
Power Supply Conditioner: Acoustic Revive RAS-14 Triple-C |REVIEW|
Passive filter EMI/RFI: VERICTUM Block |REVIEW|


Speaker stands: ACOUSTIC REVIVE (custom)
Hi-Fi rack: FINITE ELEMENTE Pagode Edition |ABOUT|
Anti-vibration platforms: ACOUSTIC REVIVE RAF-48H |ARTICLE|

  • HARMONIX TU-666M "BeauTone" MILLION MAESTRO 20th Anniversary Edition |REVIEW|


Phono preamplifier: Phono cartridges: Tonearm (12"): Reed 3P |REVIEW|

Clamp: PATHE WINGS Titanium PW-Ti 770 | Limited Edition

Record mats:


Headphone amplifier: AYON AUDIO HA-3 |REVIEW|

Headphones: Headphone Cables: Forza AudioWorks NOIR HYBRID HPC