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Power amplifier



Manufacturer: EXOGAL AUDIO
Price (when reviewed): 15.500 PLN

Contact: 4657 Aspen Ridge Circle
Eagan, MN 55122, USA


Provided for test by: AUDIO ATELIER

do not know if you remember the digital amplifier TacT Audio Millenium, which made a lot of fuzz on the marker several years ago, and set a new direction followed today by a large part of the audio world. In Poland its legend was built by Andrzej Kisiel, chief editor of "Audio" magazine, who used it as a reference amplifier, as well as by the owner of ESA who also used it as his main amplifier. This digital amp appealed to the progressive audiophiles, who always seek for novelties and for whom progress in audio has not ended up with a directly heated 300B triode in 1938 and horn loudspeakers from the same period.

Presented in 1998, Millennium was the first commercially available digital amplifier, or in other words, a Power DAC. In contrast to analog class D amplifiers, the processor in the Millennium enables the Equibit algorithm to digitally select the correct pulse width combination from among 256 possible width choices. The input signal was so converted to 8-bit, and to an analog signal only in the output analog filter.

Looking at Ion, checking its technical parameters, I assumed that this is another realization of such a project, maybe even an interesting one, but still typical. I prepared a short part for this review explaining the principle of operation of the class D amplifiers, the difference between the analogue and digital class D amplifiers and finally also mentioned class G amps. In the meantime, I received answers to my questions from the amplifier's designer, Mr. Jeff Haagenstad and all I could just throw that all away ...

Chief Executive Officer

Wojciech Pacuła: Is Ion a so called „switching amplifier”?
Jeff Haagenstad: It is NOT a switching amplifier. It doesn't take a musical signal from the Comet, it takes Data from the Comet which is used to control the Power. It is essentially 4 computer networks between the two boxes that they use to talk to each other. It's not a PWM design at all. It's direct control of Power from the PowerDAC circuit. It's a totally new concept.

I am not sure that I understand – does it mean it is not a class D amplifier? Neither analogue nor digital one?
Neither. It is a PowerDAC. It is a DAC that controls signal in the Power Domain, as well as the Time and Frequency Domains. It is quite literally a power supply that drives the speakers directly. This allows us to render analog transients at digital speeds so it is very clear and articulate - way more so than any other Class D design and in many ways more than Class A design.

Just curious – is it a similar concept to the one of Wadia's PowerDAC?
It's the same concept as the old Wadia PowerDAC but the technology didn't exist until recently to make it work reliably.

What kind of signal does HDMI cable carry? - Digital or analog?
It carries digital signals that connect the computing circuitry in the Comet to the computing circuitry in the Ion. Together they essentially become an integrated pipeline processor where the time and frequency are processed in the Comet and the Power is processed in the Ion.

What makes it special? - I know you worked on it a long, long time...
Well, as I said earlier, it renders analog transients at digital speeds. One of the biggest problems with classic digital amplifiers is that the momentum of a rising or falling voltage makes the output want to continue rising or falling. A digital amplifier needs to shunt off this overshoot or undershoot using filters and that results in the "smearing" effect that makes digital amps sound muddy or veiled.

A PowerDAC controls not only the rise and fall time of the waveform, but it also controls the overshoot and undershoot so the transient stops precisely where it is supposed to. Since it's being tightly controlled by a dedicated DSP, we can render an exact analog waveform and since the waveform is calculated using high-order mathematics as opposed to approximation, there are no noise floor artifacts which means that the output is also extremely quiet. So in a nutshell: it's a very quiet and articulate amp which allows it to recreate the sound image very precisely.

How about speaker cables - is Ion sensitive to their inductance?
The Ion doesn't much like lacquered magnet wire-style speaker cables. These types of cables have incredibly high capacitance (on the order of 10,000 to 12,000 times) compared to traditional speaker cables and badly built and maintained cables of this type can cause a "kickback" into the Ion. Since the Ion is essentially a power supply to the speakers, the last thing it wants to see is an unexpected voltage spike coming back in from the speakers.
Actually, regular Class D amplifiers don't perform very well with these cables either. The kickback voltage will eventually cause a lot of digital amplifier designs to eventually fail. Thus we don't recommend cables of this type. Other than that limitation, it's not very fussy at all and performs well with any well-insulated cable. (The high capacitance comes from the thin enameling used to prevent these cables from shorting. The wires are so close together that they have very high capacitance. Also, since the enamel is very brittle, the cables can get micro-fractures and cause short circuits.)

Is Ion's firmware upgradeable?
Yes, just like the Comet, the Ion's firmware is fully upgradeable.


The first Exogal product was digital-to-analogue converter named Comet. It is a small, great-looking DAC featuring several digital inputs including: an asynchronous USB (32/384 | DSD128), AES / EBU (24/192), S / PDIF (24/192), Toslink (24/96) and analog RCA. The Comet features also a function of a preamplifier – the analogue output signal is fully adjustable in 100 steps, and the adjustment is done in the digital domain.

Comet sports one more connector - HDMI, which was intended for digital connection with a product still in development - the Ion PowerDAC. As I wrote in my previous test, people behind this company have a vast experience in digital audio, and D/A Converters in particular. They initiated their first project of this type while still working for Wadia. The product was named Power DAC Wadia 790 and despite being able to use that experience to their advantage they have still worked on the Ion for many years.

Exogal amplifier is designed to work exclusively with Comet DAC and no other source - there are no analog inputs, and the only digital one is HDMI input. Manufacturer calls it Exonet interface. This link not only transmits signal, but also allows user to control the amplifier using Comet's remote control. The specifications of this small device is quite impressive: its nominal power at 8 Ω load is 100 W per channel, with150 W peak power, the minimum load is 2 Ω (which means user doesn't have to worry about difficult to drive speakers), THD is 0.03% (@ 1W @ all frequencies into 4 ohms). And all is fit into a nice looking, solid chassis measuring only 47.6 x 190 x 292 mm.

Connecting the amplifier is simple. First, one connects it with quite large external SMPS. It's not particularly nice-looking so a longer cable would come handy allowing user to hide the black box somewhere behind the rack. In any case, we plug it into one of the three slots on the rear panel. The second one we are going to use is the HDMI input, which allows us to connect it to the Comet DAC. There are many high quality HDMI cables available on the market so one can try different ones to find the best among them. And finally there are speakers outputs. The whole operation should take you no more than 5 minutes from opening the box to having system up and running.

PowerDAC Ion is made in USA.

During this test CDs were my priority, as they had been when I reviewed Comet. My Ancient Audio Lektor AIR V-edition CD Player featuring Philips CD Pro2 LF mechanism was used as a transport. It was connected to DAC using Acrolink Mexcel 7N-DA6100 digital coaxial cable. All discs were de-magnetized using Acoustic Revive RD-3 prior to listening.

I divided my test into two parts. During the first part I compared power amplifiers:
• digital signal was delivered from transport to Exogal Comet DAC, then from its analogue outputs to Ayon Audio Spheris III preamplifier and later to Soulution 710 power amplifier driving Harbeth M40.1; in this setup Comet work exclusively as DAC, with output set to 0,0 dB
• digital signal was delivered from transport to Exogal Comet DAC, then from its HDMI output to Ion PowerDAC's HDMI input.
The latter part allowed me to compare two complete systems – my reference one and the one with Exogal Comet + Ion, with Lektor as transport, and in both cases I used my Harbeth M40.1 loudspeakers.

Devices handling digital signals are very sensitive to vibrations, so I placed DAC on Acoustic Revive wooden stands, and the amplifier on the CP-4 discs (more HERE). The second problem of this type of products is large RF noise. To minimize this risk, I used Verictum X-Block passive filters for both, DAC and amplifier. For the amplifier I used Harmonix X-DC350M2R Improved Version (Polish) power cable.

EXOGAL in „High Fidelity”
  • AWARD: BEST PRODUCT 2016 - Exogal COMET PLUS DAC - D/A Converter
  • REVIEW: Exogal COMET PLUS DAC - D/A Converter

  • Albums used for the test (a selection)

    • Cantate Domino, dyr. Torsten Nilsson, Oscar Motet Choir, Proprius/JVC Victor Company XRCD 7762, XRCD2 (1976/2003)
    • Carlo Gesualdo de Venosa, The Complete Madrigals, Delitiae Musicae, Marco Longhini, Naxos 8.507013, 7 x CD (2013)
    • Chopin, Piano Concerto No. 1
    • Ballades, Seong-Jin Cho, London Symphony Orchestra, Deutsche Grammophon/Universal Music LCC UCCG-1755, SHM-CD (2016)
    • Diana Krall, All for You, Impulse!/JVC 532 360-9, XRCD24 (1996/2010)
    • John Coltrane, Coltrane’s Sound, Atlantic/Rhino R2 75588, „Atlantic Jazz Gallery”, CD (1964/1999)
    • Mark Knopfler, The Trawlerman's Song EP, Mercury 9870986, CD (2005)
    • NOVI Singers, NOVI in Wonderland, MPS/Edel/Victor Entertainment NCS-10139, K2HD Pro Mastering CD (1969/2016)
    • Rival Sons, Great Western Valkyrie, Erache Records/Hydrant Music QIHC-10059, CD (2014)
    • Sohn, Tremors, 4AD/Hostess CAD3403CDJ, CD (2014)

    Japanese issues available at

    There is this old saying in audio that "big gives big." Ie. if we play music using big loudspeakers with large drivers we shall get a big, powerful sound. Same goes for amplifiers - the larger the device, the more power. For amplifiers in Class D and Class G, however, one needs to modify this belief, because it has nothing to do with reality. Manufacturers used this fact and maybe two years they created a whole new category of audio systems. These are of mini and midi size - which isn't a new idea - but these offer a true high-end performance, and that's definitely new. To support this theory let me mention such examples as systems by: Chord Electronics (Hugo TT + TToby; Polish), or Bel Canto Design (‘Black’ ASC1 + MPS1). Now we can add to this group also Exogal (Comet + Ion).

    With this in mind, looking at the “baby” amp placed on the shelf above the chunky, mighty Soulution 710, I couldn't rule out a possibility of it delivering a large scale sound, or powerful bass. As it turned out I was right not to. The very essence of the Exogal system's performance is based on energetic and rhythmic sound. I would even say that it was a presentation with a greater momentum and more pulsating bass than the one I get from Soulution. This does not mean that Exogal is a better amplifier, after all, we are talking about devices from two totally different price levels (and it's the quality one pays more for). What it means is that with the American amplifier one does not need to worry about one's loudspeakers being properly driven even in a large room, nor about presentation being very energetic.

    The Ion PowerDAC delivers amazingly smooth and clean sound. The vast majority of devices of this type modifies sound in a similar way to that of tube amplifiers, ie. they round the attack and "sweetened" treble up and Exogal is no exception. All recordings played with it were beautifully smooth, and when vocals were added to the mix another feature became perfectly clear – an ultimate purity of the sound. Moved by how the Carlo Gesualdo de Venosa's music sounded like right after that I listened to a modern electronic music the Sohn's album Tremors and my impressions were exactly the same. I could play music very loud, and yet it remained on THIS side of force. As if from an Exogal's dictionary word like: "rough", "annoying", "bright", etc., were completely eliminated.

    The most obvious description of this sound would be “warm”, but that's not entirely true. Treble here is strong, clear, it's more present here than with my reference system. Also bass surprises with its extension and purity. With the aforementioned album Tremors it created an incredible effect, because it's rich with slammy bass. Exogal's amplifier controlled the bass very well and without softening it. The amount of treble and quality of bass does not allow one to place an equal sign between 'Exogal' and 'warm'.

    On the other hand if we look at the Ion's sound character we might change our opinion on the topic. It has a "golden" flavor, because the attack is slightly rounded - the further up the band, the more so. Therefore, the strong treble doesn't sound aggressive, while the sound is very open. The percussion cymbals, which was most obvious with jazz tracks, do not form heavy, tangible sources, but rather are slightly modified to give them more “flow”. I will say this: it is not a perfectly neutral presentation, but it will appeal to many "High Fidelity" readers. It will be extremely difficult to get to the point where the tweeter will become an enemy and start to attack us, although it will always be very active.

    So what we get is: purity, extension, openness, gold “flavor”, rhythm (great!), and a liveliness that most Class-D amplifiers miss. What Ion has in common with other, even the best applications of this technology, is the resolution, which in its case is not a priority. I do not know if it's even possible, but I am still to hear this type of amplifier, which could differentiate images, timbre, dynamics and soundstage in as good a way as the best class A and AB amplifiers. In this regard, Exogal is a typical child the technology.

    Also the soundstage is rather typical and similar to what I heard once with the Jeff Rowland Continuum S2 Integrated. We can “see” large phantom images, the sound has momentum, and the volumes of sound are displayed perfectly. The whole has a common denominator, based on placing the sound in a semicircle in front of us. It's a tight, dense space with a lot happening there. Rear plans are pulled closer o the front, which results in sound sources being slightly enlarged, and it is probably this modification of the presentation that creates this impression of sound "density". If the information allocated exactly to one of the channels, as in the recordings from the 1950s and 1960s, the presence of instruments, voices, etc. is extremely intense.


    I have to fight the temptation to treat Exogal set as something special, something from “outside the system”. The fact that it is compact and uses techniques that only in the XXI century were properly developed, does not make it something worse, that one needs to treat leniently. This is a bona fide audio system and you have to get used to the fact, that more and more of audio systems will look like this one. Its small size and main stream design open the door to our "audiophile fortress" for the people who do not want to have some ugly, large, awkward-to-use audio products in their houses.

    The Exogal system is not cheap, you can even say that it is one of the more expensive proposals of that type. But, as I tried to explain, it has clear advantages - see above. Its sound is open, clean and precise, and at the same time very listener-friendly. High output really translates into the unconstrained presentation, so you do not have to be afraid of using even some large loudspeakers. The amplifier's sound resembles one of the tube device, but only with regard to the leading edge of the sound, which is rounded and "polished". Together this creates a presentation so recognizable, it would be easy to make a decision and possibly replace some huge, occupying half of the room setup for something "like" this one :)

    Ion PowerDAC amplifier is a compact device, measuring 47.6 x 190 x 292 mm and weighing 4 kg. It's a two-box device with the amplifier and a separate 24 V DC power supply. The latter is purchased from an external supplier. It connects to the amplifier with a short cable umbilical terminated with a 4-pin Neutrik XLR plug.

    The chassis of the amplifier is made of a precision milled aluminum block. On the front there is a single, multi-color LED that using color and flashing indicates the status of the device. On the back there are two pairs of gold-plated speaker connectors, HDMI input for connecting the Comet DAC. The interface between Comet and Ion is called "Exonet." It is a two-way link, and when Ion is connected with Comet the latter in addition to the analog output and headphone one, allows user to use Exonet output.

    On the rear panel one finds also trigger sockets and USB control connector plus the power inlet. On the bottom manufacturer used an acrylic plate with steel balls that serve as device's feet. The device tends to slide on the wood, so one should consider using some anti-slip elements underneath.

    The entire interior is occupied by a single PCB divided into two segments - left and right one, or left and right channels. In the middle there is a big DSP chip, probably power supply modulator, and at the front additional, smaller plates, which are elements of the power supply section. Closer to the back there are power transistors - four per channel. It seems that the output is bridged, with LC filters on both branches. The transistors bolted to the upper baffle are MOSFETs. Looking at this circuit it might be hard to believe that this device is capable of delivering such a fantastic performance while not having large heat sinks or power supply transformers. But this is the twenty-first century.

    Specifications (according to manufacturer)

    Power output: 100W 8 ohms per channel, 150 watts peak power
    Minimum load: 2Ω per channel
    Peak output current: 10 A per channel
    Frequency range: 5Hz – 22KHz
    THD: 0.03% THD (@ 1W @ all frequencies into 4 Ω)
    Output noise: 170 μV VRMS A-weighted 10Hz-20KHz
    Damping factor: > 30 into 1Ω | >100 into 4Ω
    Output impedance (@100 Hz): < 0.03 Ω
    Dynamic range: >105dB (A-weighted)
    Power consumption: max 800W | typical 50W
    Power consumption in standby: <2W
    Dimensions: 47,6 x 190 x 292mm
    Weight: 4.08 kg



    - Turntable: AVID HIFI Acutus SP [Custom Version]
    - Cartridges: Miyajima Laboratory KANSUI, review HERE | Miyajima Laboratory SHILABE, review HERE | Miyajima Laboratory ZERO (mono) | Denon DL-103SA, review HERE
    - Phono stage: RCM Audio Sensor Prelude IC, review HERE

    - Compact Disc Player: Ancient Audio AIR V-edition, review HERE

    - Line Preamplifier: Polaris III [Custom Version] + AC Regenerator, regular version review (in Polish) HERE
    - Power amplifier: Soulution 710
    - Integrated Amplifier: Leben CS300XS Custom Version, review HERE

    - Stand mount Loudspeakers: Harbeth M40.1 Domestic, review HERE
    - Stands for Harbeths: Acoustic Revive Custom Series Loudspeaker Stands
    - Real-Sound Processor: SPEC RSP-101/GL
    - Integrated Amplifier/Headphone amplifier: Leben CS300XS Custom Version, review HERE
    - Headphones: HIFIMAN HE-6, review HERE | HIFIMAN HE-500, review HERE | HIFIMAN HE-300, review HERE | Sennheiser HD800 | AKG K701, review (in Polish) HERE | Ultrasone PROLine 2500, Beyerdynamic DT-990 Pro, version 600 - reviews (in Polish): HERE, HERE, HERE
    - Headphone Stands: Klutz Design CanCans (x 3), review (in Polish) HERE
    - Headphone Cables: Entreq Konstantin 2010/Sennheiser HD800/HIFIMAN HE-500, review HERE

    - Portable Player: HIFIMAN HM-801
    - USB Cables: Acoustic Revive USB-1.0SP (1 m) | Acoustic Revive USB-5.0PL (5 m), review HERE
    - LAN Cables: Acoustic Revive LAN-1.0 PA (kable ) | RLI-1 (filtry), review HERE
    - Router: Liksys WAG320N
    - NAS: Synology DS410j/8 TB
    System I
    - Interconnects: Acrolink Mexcel 7N-DA6300, review HERE | preamplifier-power amplifier: Acrolink 8N-A2080III Evo, review HERE
    - Loudspeaker Cables: Tara Labs Omega Onyx, review (in Polish) HERE
    System II
    - Interconnects: Acoustic Revive RCA-1.0PA | XLR-1.0PA II
    - Loudspeaker Cables: Acoustic Revive SPC-PA

    System I
    - Power Cables: Acrolink Mexcel 7N-PC9300, all system, review HERE
    - Power Distributor: Acoustic Revive RTP-4eu Ultimate, review HERE
    - Power Line: power cable Oyaide Tunami Nigo (6m); wall sockets 3 x Furutech FT-SWS (R)
    System II
    - Power Cables: Harmonix X-DC350M2R Improved-Version, review (in Polish) HERE | Oyaide GPX-R (x 4 ), review HERE
    - Power Distributor: Oyaide MTS-4e, review HERE
    - Stolik: SolidBase IV Custom, read HERE/all system
    - Anti-vibration Platforms: Acoustic Revive RAF-48H, review HERE/digital sources | Pro Audio Bono [Custom Version]/headphone amplifier/integrated amplifier, review HERE | Acoustic Revive RST-38H/loudspeakers under review/stands for loudspeakers under review
    - Anti-vibration Feets: Franc Audio Accessories Ceramic Disc/ CD Player/Ayon Polaris II Power Supply /products under review, review HERE | Finite Elemente CeraPuc/ products under review, review HERE | Audio Replas OPT-30HG-SC/PL HR Quartz, review HERE
    - Anti-vibration accsories: Audio Replas CNS-7000SZ/power cable, review HERE
    - Quartz Isolators: Acoustic Revive RIQ-5010/CP-4

    - FM Radio: Tivoli Audio Model One