November 2023

AGD Audion Mk III Monoblock Amplifier Review
Art deco style with an emotionally engaging, tonally rich, and high-resolution sound.
Review By Rick Becker

  It was love at first sight when I discovered the new AGD Audio at Rocky Mountain Audiofest back in 2019. My review came out in the February 2020 issue and it was awarded a Best of 2020 Blue Note Award. Now, four years later, it still puts a smile on my face when I turn it on. It's priced at $7850 per pair in a satin finish and $8600 in full polish, a modest price increase from the $6800 in satin and $7500 in polished when first introduced. Given how quantitative easing to deal with COVID-19, along with supply chain disruptions and opportunistic suppliers has led to inflation, this is sadly understandable. Factoring in the increase in sound quality brought first by the Mk II, and now the Mk III, well, that's what this review is all about.

Insofar as I've reviewed these two updates as well as the Tempo di GaN stereo version of these monoblocks, the Andante preamplifier, and the more powerful Vivace monoblocks, some might call me a fanboy of this relatively new brand — a merit badge I will proudly wear. Yet close inspection of my show reports will reveal that I've been critical of his rooms on occasion. When Alberto has been given a Best Rooms Award, it's because he has earned it. Sometimes the speakers he has teamed up with have been less successful, due to challenging set-up requirements in the small rooms.

Alberto, of course, is Alberto Guerra, an engineer who worked on the development of the GaNFET transistor, and whose passion for music drew him into high-end audio. Being of Italian descent, that passion extends beyond sound quality and high engineering standards to include the art of design. His Vivace and Audion monoblocks are at the forefront of contemporary design in high-end audio.

I could go on and on about the design and features of the Audion, but I've already done that in my initial review. I won't plow that field again. If you're interested, you can skip to my AGD The Audion GaNTube Monoblocks Review. Likewise, my review of the AGD The Audion MkII Review. It contains photos of the original and Mk II power tubes for comparison. Like the Mk II, the Audion Mk III is really all about the newest power tube. Here's what the Mk III tube looks like:

2 B or not Tube?
While some 'experts' in the forums have "pooh-pooed" Alberts's use of a KT88 vacuum tube glass shell to house the power circuitry, it is not only a very clever idea, but also has become an important element of his brand. And savvy audiophiles will acknowledge the proliferation of components with see-through chassis and internal LED lighting since AGD hit the scene. The fact that the Mk III tube is the second upgrade speaks to the validity of this design. The Mk II tubes were offered as an upgrade to owners of the original Audion for $2000 per pair. The Mk III tubes are offered at an even more reasonable price of $1500 per pair.

Like my father, I've always had a lot of hand tools, so I tackled the physical process of upgrading from the Mk II — or the Mk I for that matter, by unscrewing the top rung of the tube cage to get a grip on the tube itself. A small Allen wrench is used for this. It is necessary to wiggle the tube slightly in a circular fashion as you perform the extraction. Be sure to unplug the amp before changing the tube.

Alberto has since informed me that the tube can be simply removed (without fussing with the cage) by lifting up on the lower bulge of the tube where it fits into the socket. Well, it isn't quite so 'simple' and I found I had to wiggle the top of the tube with my thumbs as I simultaneously pulled up with my fingers at the base of the tube. The power tube, which fits snuggly, is easily aligned because the bold AGD logo is positioned to face forward. And it is easy to see when the pins and holes in the socket are aligned. White Glove? Not necessary. It is not a real vacuum tube. If I had more free time, I could come up with a joke about how many audiophiles it takes to change this tube.

Compare that tube swap with the time and effort required to ship your amps back to the factory along with the downtime in listening to music that you would experience with another brand — assuming they offered an upgrade at all. Many companies simply issue a new model and expect you to sell off your original version (at half price) and then turn around and buy the new model at full price. You take an even deeper hit if you trade it in to a dealer.

Compared to those scenarios, the brilliance of the faux tube power section becomes obvious. If you are buying the complete Audion Mk III monoblocks, the amps ship in a sturdy hard-shell flight case with the tubes already installed. Also included are two very nice power cords, white gloves, a polishing cloth, and a manual. First Class treatment.

The Listening
I can't recall how long the burn-in time was with the original version or the Mk II. It doesn't matter because the wait is well worth it. In any case, it wasn't terribly long. Likewise, the warm-up time with this amp is not long either. After a song or two, you've got the music in the pocket. More impressive was that I could sense an improvement with the Mk III tube as I walked back to my listening chair on the very first CD and from there, it only got better. Since this is a Class D amplifier, I simply left it on for a couple of weeks as I listened intermittently.

The Audion is the first solid-state amp I've found worthy of owning after two decades of being a tube guy. Still, I've continued to use my Coincident Statement Line and Phono stages, both of which are tube designs as they impart that tube glory, inner detail, and sense of air that escapes solid-state designs — at least the ones I can afford. Consequently, there is a gradual improvement in sound quality as the preamp and phono stages warm up. Sometimes I'll fire up the tubes well ahead of listening, while other times I'll just wait a couple of minutes. Vacuum tube warm-up comes with the territory. If you prefer solid-state designs perhaps you've found them to perform best when left on continuously. (I was also impressed with the AGD Andante Pre-DAC Phono Streamer if you are also looking for a solid-state preamp.) The Audion is pretty much ready to play whenever you're ready to listen. The difference between playing it cold and playing it warmed up is not great. Listening late at night when the grid has quieted down, is a more relevant consideration.

And speaking of "warmed up", being a Class D amp, it only ever gets modestly warm — never hot. Most of what you listen to will only draw a few watts in a range that is certainly more efficient than Class A or A/B, but less efficient than the impressive numbers that are often cited for Class D. Those efficiency numbers, in the >90% range, apply only at full power. Your heating and cooling bill is more profoundly influenced by the weather than the type of amp you run. Your comfort in the listening room may be another story if you are annoyed by the heating or A/C noise.

One of the prominent features of the GaNFET transistors that personify AGD amplifiers is the very fast rise time that is accomplished with very little overshoot. Musical notes just happen with no ringing or irritating attack. This also leads to very high resolution. What differentiates the Mk III from the Mk II is an increase in inner resolution and a more sustained decay. The music 'hangs' in the air more gracefully without rushing forward to the next note. Guitar and piano notes, along with their overtones, seem to resonate a bit longer, hence sounding more natural.

Minute fluctuations in voice and sustained instrumental notes captivated my attention, leading to more emotional involvement and a greater 'you are there' experience. Overall, the music had more physicality. While the power supply in the chassis remains the same, the Mk III sounds more like my recollection of the original Vivace model which was more than twice the price. This same GaNFET KT88 Mk III tube is used in the Vivace Mk II monoblocks where it produces 250 Watts @ 4 Ohms due to the larger power supply in the Vivace chassis. Can we chalk some of these improvements up to the increase in PWM switching frequency from 400kHz in the earlier Audion models to 800kHz in the Mk III? Quite likely.

The music was more relaxing, not in the sense of warming me up like a cup of hot chocolate on a winter night, but because the increased resolution required less cognitive brain power to interpret what I was hearing. Vocals of old bluesmen on recordings made long ago were more easily (but still not completely) understood. There is a limit to understanding the dialect as well as the recording quality, after all. But I was left wondering "What's that line?" a lot less often. Similarly, the notes of instruments did not blend into the territory of adjacent musicians.

It was easier to follow the lines of a chosen instrument, even if was placed further behind another on the soundstage. Likewise, backup singers, often placed far to the back or side of the stage, came through with much better intelligibility and placement. Wilson Philips, my go-to group for female three-part harmony was more delineated and the wall of sound behind them became an ensemble of actual instruments rather than a musical interpretation of a French impressionist painting.

The relaxation factor mentioned above led to effortless listening without fatigue. And while the Mk I and Mk II already had a proverbial silent black background, the Mk III was almost spooky in that regard, though the Stack Audio Auva footers, reviewed elsewhere in this issue, certainly contributed in that regard when used on my source components and speakers. The noise floor has dropped to a claimed -140dB without being A-weighted. This is incredibly low for a Class D switching amplifier. Yet I never felt like I was drinking distilled water because the resolution and outstanding transparency of the Audion revealed a healthy dose of room tone or ambient noise from the recording venue. The Audion put me in the venue rather than a sterile musical chamber. I typically felt like I was there, somewhere that the music was coming from.

Power
The 85 Watts per channel @ 8 Ohms, 170 Watts @ 4 Ohms, of the original Audion was plenty sufficient for a lot of speakers in a lot of different rooms, but not all. I felt the original Mk I was sufficient for the Kharma speakers at 89dB/W/m efficiency with benign 8 Ohm impedance. This speaker is a relatively easy drive so the Audion worked even in my large room as long as I didn't push much past 100dB on musical peaks (measured at the listening position.) Power-wise, the Mk II didn't seem much different, though sound quality certainly improved.

Earlier, I had been using the Audion Mk II to power the LCH subwoofers (reviewed elsewhere in this issue) and Eddy Wong's Magic Tube Research tube monoblocks with 18 Watts per channel from parallel 300B tubes to power the Kharma. The LCH is more power-hungry than the Kharma, requiring 100 to 400 wpc, and the Audion Mk II was just below the lower edge of acceptability with the subwoofer. When Mark Heusi sent a 400 Wpc D-Sonic amp, the LCH subs came alive, dynamically, but lost a bit of tonal quality and inner detail. Still, the D-Sonic was an acceptable improvement.

The arrival of the Mk III power tubes for the Audion was a game changer. Now, rated at 100 watts @ 8 Ohms, 200W @ 4 Ohms, with >30A max current capability, the monoblocks drove the LCH subs with even greater sound quality and were dynamically sufficient for the subs, pleasantly filling in the low bass at my normal, though not 'head-banging' listening levels.

The increase in power was readily apparent and seemed like a lot more than just 15 Wpc @ 8 Ohms. That there was no change to the power supply in the chassis made the improvement even more impressive, especially considering that each monoblock weighs a mere 7 pounds. The small form factor even lets you significantly downsize your rig without resorting to a stereo or integrated amp with their compromised performance.

Combining the increase in power with the increase in sound quality the Audion now comes very close to the sound quality of Merrill Audio Element 116 monoblocks at $24,000 per pair. The Element 116 has three times the power to go along with three times the price. I've heard the Merrill at a private audition at Distinctive Stereo in New Jersey and again at Capitol Audiofest. The price and power differentials here will be the defining factors for many people. A more apples-to-apples comparison would be to move up the AGD line to the new flagship SOLO at $23,500/pair which puts out 300 Watts each @ 8 Ohms, and 500 Watts each @ 4 Ohms. I will be keeping an eye out for that one at future shows.

Value And Mods
When I invested in the original Audion I felt like it could be a 'forever' amp as long as I shied away from speakers with difficult-to-drive loads or very high current needs. The upgrade to the Mk II level, two years later, kept me very close to state-of-the-art Class D design. For this review, I simply exchanged the GaNFET power tubes to achieve Mk III status.

I left the Synergistic Research Purple fuse in the amps which were placed on a Symposium Acoustics Svelte Shelf sitting atop my tube amps. They were powered with Synergistic Research Atmosphere Excite SX power cords. No other aftermarket products were applied, though I suspect adding Stack Audio Auva SE footers (reviewed elsewhere in this issue) might squeeze a bit more sound quality out of them. So equipped, the Audion gracefully drove my Kharma to 102dB peaks, much louder than I typically listen.

For a pair of monoblocks that cost well under five figures and approaches state-of-the art for any solid-state amplifier design, this GaNFET Class D amplifier represents a very high value and deserves the attention of fervent tube lovers as well. Given that it may well be your 'forever' amp, even the extra cost polished finish warrants consideration for the class and elegance it will bestow upon your system. The couple of times I've seen them for sale on US Audiomart they were listed well above half price and sold quickly. At least one of those sellers was moving up to a more powerful AGD amp. This is a hot amp on the pre-owned market and with this upgrade to Mk III, I'm not about to sell mine.

Summary
The new Audion Mk III, whether you buy it brand new or simply upgrade the GaNFET Class D power tube in an earlier version, represents a major advancement in this classic amplifier. While the outstanding Blue Note ratings below are only slightly improved from the Mk I and Mk II reviews, rest assured that the Mk III is an even greater advance than the Mk II. And a better value as well, despite the price increase. The Mk I and Mk II both received an annual Blue Note Award, so that should tell you where this one is headed.

Since 2018, Alberto Guera has continued to evolve his original models while also coming out with new models to address consumer demand as well as advance the state of the art in Class D amplification. Those who thrive on technical details are invited to explore his website where you will find lots of charts and measurements. I thrive on the music and I found the Mk III to be even more emotionally engaging with a more tonally rich and higher resolving presentation.

The Art Deco styling with the polished finish puts this amplifier in elite company and still puts a smile on my face every time I fire them up. Nearly four years after I bought the original I'm loving this amp more than ever and it deserves my highest recommendation.

Specifications
Type: Solid-state amplifier
Output Power: Output Power: 100 Watts @ 8Ω, 200 Watts @ 4 Ohms)
THD+N: <0.005% (10 Watts @ 1kHz)
Frequency Response: 0Hz to 50kHz
Input Impedance: 40kOhm (600 Ohm upon request)
Efficiency: >94%
Noise Floor: -140dB via balanced XLR
GaNTube KT88 Mk III PWM Frequency: 800kHz
Dimensions: 7.5" x 5.5" x 7.5" (HxWxD)
Weight: 7 lbs.
Price: $7850 in satin finish and $8600 in fully polished
Mk III Power Tubes if purchased separately: $1500 per pair

Company Information
AGD Productions
Los Angeles, California

E-mail: adgsupport@agdproduction.com 
Website: AGDProduction.com