Audionet’s Humboldt integrated amplifier ($58,750, all prices USD) is one of the most imposing amplifiers I’ve ever reviewed. For starters, it’s the most expensive product that’s taken up residence in my listening room by quite some margin. The Humboldt is also physically imposing, weighing in at just over 134 pounds and measuring 12.6″H × 17.8″W × 19.9″D. To put it mildly, it’s a brute.
Based in Berlin, Germany, Audionet has been around since 1994. Previously operating as Idektron GmbH, the company designed and manufactured high-precision medical electronics, as well as high-end audio components that were sold under the Audionet brand. Idektron went bankrupt in 2018 but emerged from the ashes under the ownership of Stefan Schwehr, who spent much of his career with automotive giant Daimler. Schwehr holds a Ph.D. from Darmstadt Technical University and has decades of experience—personal, educational, and professional—in electronics design. In conversation, Schwehr revealed that sound was his hobby, but not necessarily hi-fi. “I was so taken [up] by my work at Daimler that I didn’t have time to listen at home. But I was always surrounded by car audio at work.” He would later move on from Daimler to become CTO of Paragon GmbH, a manufacturer of automotive electronics, where he became acquainted with Idektron. When Idektron’s intellectual property and assets became available, he jumped at the opportunity to run his own company, which now operates as Audionet GmbH.
The new CEO proceeded to examine all of the company’s then-current product designs and circuits from a technical perspective. Idektron had “done a very good job,” Schwehr told me. “There was not much to innovate on the amplifier side.”
Some of Audionet’s 16 current products, which include amplifiers, preamplifiers, CD players, and a network client, have remained effectively untouched since Schwehr’s arrival in 2018, but he estimates that the designs of the newer products, developed in collaboration with Audionet’s other electrical engineers, are more than 50 percent his own. He inherited the Humboldt as a project that was approximately 60 percent complete, and together with another engineer, he improved the prototype to the point where he now proudly describes it as “maybe the best fully integrated amplifier in the world.” A bold claim.
Like all Audionet products, each Humboldt is hand-assembled in Audionet’s Berlin factory by a single technician. Ninety percent of the hulking integrated’s components are sourced in Germany. Once it has successfully traversed Audionet’s quality-assurance process, the completed amp is packed into a big Audionet-branded flight case with built-in handles that make moving the amplifier easier than it would be if packed using a more common crated approach. Still, I wholeheartedly welcomed Audionet’s North American distributor, Bill Parish of GTT Audio & Video, into my home so that he and his brother could manhandle the Humboldt down a switchback staircase and into my basement listening room. Despite having a custom-made media console fashioned from iron and 1.5″-thick reclaimed oak that I’m confident could safely shoulder the Humboldt’s mass, I decided its dimensions made the floor a better—and likely safer—option. I can’t imagine any buyer placing a Humboldt on a traditional rack.
Description
First impressions were overwhelmingly positive. The brushed-aluminum Humboldt is available in a black or silver finish, and my silver review sample looked mighty sharp. Its ribbed top panel gives the amp an interesting appearance and also provides more surface area for heat dissipation. The front panel is dominated by a large TFT screen with black text on a white background that displays input name and output level. Input names and levels are user-definable. The screen sits above a large and ludicrously weighty volume-control knob with terrific hand feel. A big power button and several control buttons round out the front panel. The side panels are bolted straight onto the chassis itself but not to one another, so there are actually narrow but evenly spaced gaps between each panel. On that point, there are a multitude of bright-red LEDs in the unit, and while you can’t see them when viewing the unit head-on, you can definitely see them when standing directly over it. An odd touch.
Around back you’ll see clear evidence of the Humboldt’s fully differential architecture. The Humboldt has two pairs of balanced (XLR) and three pairs of unbalanced (RCA) inputs, and one pair each of balanced and unbalanced outputs. The line-level inputs and outputs for the left and right channels are on opposite sides of the aluminum rear panel, as are the binding posts for speaker-level output. Those binding posts felt terrific when I began hooking up the Audionet to my system. The majority of these connectors are sourced from Furutech. Other connections include ethernet, RS-232, a pair of proprietary TosLink ports specifically intended to connect the Humboldt to other Audionet devices (these are not digital inputs), a grounding post, and the expected IEC power inlet. The included aluminum remote, with its solid heft and clicky aluminum buttons, is also designed by Audionet. Thankfully, it includes a power button—not always a guarantee on all remotes. Finally, there’s a terrific and exhaustive 71-page manual.
As you might expect, given the ambition of this product, no expense was spared for the Humboldt’s underlying architecture. There are no fewer than four toroidal power transformers inside the Humboldt’s chassis: one for each channel of the power amplifier section (850VA), one for the driver stage (150VA), and one for the preamplifier section (150VA). Under the top panel, you’ll see 12 capacitors per channel with a total capacitance of 312,000µF and fully discrete, isolated boards for each section of the big amp. The unit’s height allows for more vertical separation of components than would otherwise be possible in a traditionally sized amp, and this in turn permits better component isolation on the noise front.
Spec-wise, there’s a lot to like. The Humboldt outputs 320Wpc into 8 ohms or 460Wpc into 4 ohms, and is stable into a 2-ohm load. Now, these figures are substantial enough that this amplifier should have no problem motivating even the hardest-to-drive loudspeakers to impressive volumes, but I’ll point out that the listed 8-ohm spec does not double into 4 ohms, as you’d ideally like to see for a high-powered—and high-priced—solid-state amplifier. The wide-bandwidth amplifier has specified frequency response of 0–700kHz (-3dB), THD+N of <-100dB @ 1kHz, a SNR > 120dB, and a channel separation spec of > 140dB, 20Hz–20kHz. Maximum power consumption is a whopping 1800W.
Setup
With the Humboldt situated in my listening room thanks to Herr Parish, integrating the amplifier into my system was a straightforward affair. Out went my flyweight reference integrated amplifier-DAC, Devialet’s Expert 140 Pro, and in came Hegel’s aging—but still excellent—HD30 digital-to-analog converter. I linked the HD30 to the Audionet’s XLR inputs and my Intel NUC to the Hegel’s USB input and proceeded to connect my KEF Reference 3 loudspeakers to the Humboldt, all via Siltech Classic Legend cabling, as listed below in the Associated Equipment endnote. Both the Audionet and Hegel benefited from partnering with Siltech Classic Legend 380P power cords. Roon was my only source, playing a combination of local music and Tidal HiFi—the Humboldt has no phono stage built-in, and I’m an all-digital guy, so that was fine by me. I should note that the Humboldt also spent significant time hooked up to my KEF LS50 minimonitors, Perlisten’s S5t towers, and Vivid Audio’s Giya G3 Series 2 floorstanders. With the setup done, I was ready to go.
Listening
As lumbering as the Audionet may appear, its sound is anything but. Let’s start with latent noise: there was precious little. I had to stick my ear within 3″ of the aluminum-dome tweeter of one of my KEF floorstanders to begin to hear white noise from the loudspeaker. The Humboldt was off to an excellent start, up there with other proverbial giants in my pantheon of all-time great amplifiers, including Gryphon Audio Designs’ mighty Diablo 300, the aforementioned Devialet 140 Pro, and Benchmark Media Systems’ AHB2.
Once music began to flow, the big German amp’s topflight performance was quickly apparent. On Enya’s “O Come, O Come, Emmanuel,” from 2008’s And Winter Came . . . (16-bit/44.1kHz FLAC, WM UK / Tidal), the Celtic songstress’s enunciation of the sacred track’s opening lines was spectacular: airy and detailed yet highly textured. Perhaps most impressively, the Audionet imparted some of the most convincing holographic imaging I’ve ever experienced from a class-AB amplifier. The level of detail retrieval on offer was excellent, but as revealing as the German he-amp was, it didn’t sound clinical or sterile. I found myself restarting the track over and over to admire how the singer leapt from the soundstage following the opening bars. This was deeply satisfying, as the Humboldt proved incredibly revealing on the haunting, spare rendition of the Advent hymn.
Enamored with the Humboldt’s ease at conjuring the human voice, I quickly swapped out the big KEF Reference 3s for my KEF LS50s, knowing the diminutive speakers would disappear in a way that their floorstanding cousins would not. “Hans,” I can hear you saying, “no one would ever combine a 320Wpc integrated amplifier that retails for nearly $60,000 with a $1500 pair of minimonitors.” You’re right, but that didn’t make the results any less satisfying. On went Rüfüs Du Sol’s “On My Knees,” from his album Next to Me (16/44.1 FLAC, Rose Avenue / Tidal), and I sat slack-jawed as the track began to play. An electronic wail sounded in the distance, and I marveled at the cavernous depth of the soundstage, which seemed to extend well beyond the front wall of my listening room. No sooner had the wail faded into the ether than Du Sol’s muttered opening lines flew into my room with an immediacy and exacting definition that I found enchanting. You don’t need hundreds of watts to achieve this level of performance, but you do need superb engineering to experience a track so free of noise and distortion and so untethered from the system’s loudspeakers.
On his recent album Waves: Music by Rameau, Ravel, Alkan (16/44.1 FLAC, Deutsche Grammophon / Tidal), pianist Bruce Liu’s masterful handling of “Noctuelles,” the opening movement from Maurice Ravel’s suite Miroirs, proved delightful through the Audionet amp. The Paris-born Canadian pianist rose to prominence in 2021 after winning that year’s International Chopin Piano Competition. This led to Liu being signed by Deutsche Grammophon and a rapid rise to prominence. He made short work of this challenging Ravel piece, and his chords danced lightly into my listening room. The first 60 seconds were sublime, as Liu’s fine control bordered on preternatural. And the Humboldt kept up, exposing each hammer stroke with clarity and concision, and highlighting the voluminous recording space in Berlin’s Teldex Studio through the buttery decays of Liu’s instrument. What struck me about the Ravel piece was that I didn’t find myself focusing on one aspect of Liu’s performance. With most of the gear I review, as the hours of listening roll on, I find myself gravitating towards certain performance parameters and setting my playlist in accordance with them. Not so with the Audionet. It exhibited a dead neutral tonality, displaying no intrinsic sound characteristics of its own. Instead, I heard what I knew to be the upstream Hegel HD30 DAC’s pristine, digital crystallinity. Impressive.
Changing gears, I turned to industrial metal legend Rammstein, and the contemplative title track of the group’s 2022 album, Zeit (16/44.1 FLAC, Universal Music / Tidal). Its atmospheric opening—marked by somber piano chords through the right channel and a soloist from the Konzertchor Dresden through the left channel, all overlain with crashing waves—tees up frontman Till Lindemann’s operatic opening lyrics. Classically trained Lindemann is not, yet he’s a compelling, emotive vocalist, and “Zeit” highlights his range. I enjoyed the Audionet’s ability to define Lindemann’s rich, meaty voice, both laterally in space and in terms of microdetail. The Humboldt made him sound downright velvety, not something you ordinarily hear in concert with a wide-bandwidth, high-resolution amplifier that offers such transparent sound. And yet, it seemed to deliver the best of both worlds on the Rammstein cut.
Finally, I challenged the big Audionet amp with “Company Car,” a medley of Monty Norman’s signature James Bond theme from the motion picture soundtrack Tomorrow Never Dies (16/44.1 AIFF, A&M Records). This is a highly dynamic track, and its brass-heavy orchestration teeters dangerously towards the bright end of the sonic spectrum when partnered with the wrong electronic hardware. Despite the Humboldt’s unusual clarity while spotlighting the brash trumpets on David Arnold’s composition, what stood out for me was that my inability to discern etching or hash. Rather, there was an almost tubelike smoothness and liquidity to the portrayal of each instrument in the orchestra. I can’t imagine anyone contracting listener fatigue with a Humboldt anchoring the system.
Comparisons
Finding meaningful points of comparison for the $58,500 Humboldt is challenging. Prior to having the big Audionet amp in-house, I thought it fair to characterize my audio reviewing “beat” as being anchored in high-priced, class-AB integrated amplifiers. I’ve reviewed many such integrated amps over the last decade, including Simaudio Moon’s 700i v2 and Constellation Audio’s Inspiration Integrated 1.0.
But the previously mentioned Gryphon Diablo 300 definitely springs to mind. That amplifier—now replaced by the Danish manufacturer’s brand-new Diablo 333—offers a similarly mammoth 300Wpc into 8 ohms but doubles that figure into 4 ohms and produces a remarkable 950Wpc into a 2-ohm load. The Diablo 300 stands in dark, brutalist contrast to the Audionet’s more neutral, minimalist vibes. While I found that amp to be immensely enjoyable, its sound deviated from strict neutrality, lending a dash of golden sweetness to the midrange that—as I wrote back in 2016—lent vocals “greater bloom and vivacity” than I was used to hearing. Yet, the mighty Gryphon retailed for $17,990 (when last available) without its optional DAC or phono boards, and I feel confident in saying that the Gryphon integrated was also extremely quiet, highly resolving, and what I would have considered at the time to be an endgame-level integrated amplifier. Aural memory is fickle at best, and while the Humboldt betters the Diablo 300 in terms of neutrality and edges it out on the transparency front, it does so at more than three times the price while offering similar power output and a similar handmade heritage.
Vinnie Rossi’s L2i Special Edition integrated amplifier (discontinued; $18,995 when available) was a different animal. Its 100Wpc into 8 ohms is flyweight when compared to the Audionet’s heavyweight power spec, but when it was here for review, it looked and felt every bit as special as the Humboldt. This is further reinforced by its underlying design, which featured a MOSFET-based class-AB amplifier circuit, but one that could leverage a pair of Electro-Harmonix 300B Gold direct-heated triode (DHT) vacuum tubes in the input stage. I say could because the tubed input stage was defeatable, allowing the amplifier to run in hybrid mode with the tubes engaged, as well as in a fully solid-state mode. Effectively, you got two amps in one. In solid-state mode, I found its sound similar to the Humboldt’s: very quiet, clean, and resolving. Like the Diablo 300, the L2i SE couldn’t quite match the Humboldt’s outright transparency to source material. And it obviously fell well short of the Humboldt on both the power and current fronts. But based on its looks, build quality, and unique design—in addition to having a solid aluminum remote control that is one of the best I’ve ever used—I feel the L2i belongs in the same conversation as Audionet’s Humboldt.
But remember: There are no points for second place. In terms of outright performance, the Audionet Humboldt is superior to each of the amplifiers I’ve mentioned. If you want the best, be prepared to pay for it.
Conclusion
Audionet’s Humboldt integrated amplifier isn’t just a reference-level integrated amplifier; it’s a statement-level integrated amplifier. At a scarcely believable $58,500, it damn well should be. And after months of listening across a variety of partnering loudspeakers, I can report that it’s not only the highest performance class-AB integrated amplifier I’ve reviewed but also the most enjoyable. I found its combination of deep power reserves, extreme transparency, and cavernous soundstaging beguiling. Allied to a dead-neutral frequency response, I’m not sure you could ask for anything more from a topflight, modern integrated amp. It’s costly, but the best often is.
. . . Hans Wetzel
hansw@soundstagenetwork.com
Associated Equipment
- Speakers: KEF LS50, Reference 3; Perlisten S5t, Vivid Audio Giya G3 Series 2.
- Integrated amplifiers: Devialet Expert 140 Pro.
- Digital-to-analog converter: Hegel Music Systems HD30.
- Source: Intel NUC computer running Roon and Tidal HiFi.
- Speaker cables: Siltech Classic Legend 680L.
- Analog interconnect cables: Dynamique Audio Shadow (RCA), Siltech Classic Legend 680i (XLR).
- Power cords: Siltech Classic Legend 680P.
- Digital interconnect: Siltech Classic Legend 380 USB.
Audionet Humboldt Integrated Amplifier
Price: $58,500.
Warranty: Five years, parts and labor.
Audionet GmbH
Brunsbütteler Dam 140 B
13581 Berlin
Germany
Phone: +49 (0) 30 2332 421 0
Email: service@audionet.de
Website: www.en.audionet.de
US distributor:
GTT Audio & Video
356 Naughright Road
Long Valley, NJ 07853
Phone: (908) 850-3092
Email: av@gttaudio.com
Website: www.gttaudio.com
