February 2020

AGD "The Audion" GaNTube Monoblocks Review
Class D reaches the upper echelon of high-end audio.
Review By Rick Becker

  Back at the turn of the millennium you could put together a pretty good audio system for $10,000, and you could listen to many of those components in a local brick & mortar store if you lived in a decent size city. Sure there was some stratospherically priced gear in the $10,000 to $20,000 range you might be able to see if you went to one of the audio shows on the left or right coasts. Then along came "quantitative easing" and the internet. Gear got more expensive, the brick & mortar landscape eroded and major as well as regional audio shows proliferated. Eventually, higher prices seemed to have attracted more well-heeled patrons to the hobby, not unlike what happened to the bicycle industry a generation or two earlier. Or maybe those who were in their forties in the 1990s simply moved up the ladder in their careers or inherited wealth from the heroes of WW II.

The technological landscape of high-end audio, like the marketing landscape has also evolved with the major impact first, of digital gear, then, our current tsunami of streaming technology. An undertow caused by the cost of higher education outstripping the rise of real wages has been a double-edged sword, eroding debt-laden younger folks who might otherwise enter the hobby, as well as leaving their parents with drained bank accounts, struggling with their own debt. The rise of online shopping dovetails with the decline of the mall and people spend a larger portion of their income eating out to give themselves more face time with society — as dangerous as that seems to have become with the rise of gun violence. High End audio, on the other hand, is largely more isolationist, favored by those who can afford it and those who choose music over opioids as their drug of choice.

And then there are the gearheads among us. There are always gearheads. Some of them are manufacturers determined to make the wheel obsolete; others are determined to have the best audio system they can amass, targeting goals such as "loudest", "bad-assed" or "most accurate reproduction of live, un-amplified music." These are generally known as consumers, and sometimes, audiophiles. Many of them are attracted to shinny objects, for better or worse, and are simply acquisitionists — people prone to acquiring more "stuff".

Falling In Love With Chrome
Maybe it was the polished stainless steel fenders on my Schwinn bicycle when I was a kid, but I've always been attracted to shinny objects. Back in the late 1950's you couldn't put too much chrome on a car. Today, as an audiophile, I'm supposed to be concerned with sound quality and when I was getting started in the pursuit, that was my mantra. That, and do it at the best possible price. I gobbled up knowledge and experience like a free-range chicken from magazines, internet newsgroups, audio shows and even brick & mortar stores as I traveled. It was almost a decade before I was invited to write for Enjoy the Music.com and even then, my rig was little more than a toe-hold in the hobby. Certainly, no shinny objects.

That all changed with the purchase of the Statement Preamplifier and Statement Phono Preamplifier from Coincident Speaker Technology. One was a review sample, the other bought on reputation. I justified the bling factor by rationalizing that the preamps and their massive power supplies matched the shiny fenders on my vintage Suzuki motorcycle in the garage. Well, perhaps my ego needed an excuse. In any case, it didn't take long for the polished stainless steel preamps to feel completely at home with my torn jeans, old dress shirts with frayed collars and bookcases filled with vintage LPs collected at garage sales and flea markets. There was no arguing that the music sounded appreciably better.

Next up was a shiny equipment rack from Codia Acoustic Design that I honestly doubted would be any better than the collection of high-tech footers and solid wood shelves that had previously been so impressive. I ordered it in all-chrome, forgoing the two-tone chrome and gold finish since all-chrome was the finish importer Bernard Li said would be most easy for him to re-sell. I honestly thought I would be returning it. A $5000 equipment rack just didn't compute with my sense of value, shiny chrome finish or not. Until I heard the music. A couple of years later the 3000BAB rack was replaced with the 3000 Diagon that sounded even better, once again with light wood shelves and polished chrome pillars and hardware. Damn if the rig didn't look elegant — in spite of my worn jeans and blues LPs with water-stained jackets.

I love audio shows. The endless rooms filled with gear that I've only read about or have yet to discover are a candy shop, circus and concert hall rolled into one. My first trip to AXPONA in 2019 was no exception, except it was much bigger than the Canadian shows I call home. It was there, on the 14th floor that I encountered Alberto Guerra of AGD Productions with a quartet of his Vivace monoblocks ($15,000/pair) driving the Ocean Way Audio horn loaded Monterey speakers ($34,000) created by multiple Grammy Award winner Allen Sides in bi-amp configuration. (Alberto and Allen are currently collaborating on an active speaker that may be ready for AXPONA 2020 or RMAF 2020.) As strange looking as they were with a large single tube sticking out of the top, they begged investigation. Each monoblock put out 100 Watts into 8 Ohms, 200 Watts into 4 Ohms and was stable down to almost 0 Ohms. Furthermore, while those were tubes sticking out of the top, they were not vacuum tubes. Alberto called them GaNTubes. While it makes for a rather ingenious way to provide easy swapping of the active circuitry, it is very unlikely they will fail or suffer age related degradation. You can let your grandchildren worry about replacing them decades from now.

The WHAT?
The circuitry of the AGD amps use Gallium Nitride FET transistors which offer much faster reaction (rise time) to signal input than traditional silicon MOSFETs. He called them GaNFets, and until recently they were only commonly used in high frequency military applications such as radar. Designed and manufactured by International Rectifier (IR), a legend and pioneer in the power electronic industry that among other things, made possible the revolution of PCs and Notebooks with the invention of the power MOSFTs. 

IR, the oldest and the last independent American company in power electronics, was acquired in 2015 by Infineon (Infineon is a German manufacturer with 40k employees and annual sales around $6B.)

He knows them well because he helped design them. Although Alberto is Italian, he has been in the US for 23 years. Here, his proprietary version designed for audio were used in the Class D power stage seen inside the tube. He spoke to me about high frequency and zero crossing switching, but I'm not an engineer, so you'll have to check out his website (link at bottom of page) or do a search if that's of interest to you.

So, can you hear the difference, you ask? Well, you'll have to read on, but the fact that I noted this room as one of the Best Rooms at AXPONA should be a significant clue. It was early at the show and for an amp of an intriguing design, yet with a $15,000/pair price tag I wasn't interested yet in a review sample. Alberto told me the design originated from a collaboration with Bo Christensen, a renown Danish designer, but Alberto further modified it to display the GaNTube, a decision that leaves it vulnerable in active households with kids and pets. In this price range, however, they are more likely to be treasured in a serene dedicated listening room. Beauty is in the eye of the beholder, and I've long argued that beauty matters, so time will tell how the market responds. In my mind, I was thinking about what gorgeous amplifier might be found in the next room or on the next floor at the show. So much new gear; so little time. Nevertheless, I thought about the Vivace monoblocks time and again over the summer.

RMAF 2019 Display

Chicago was one day away from home in Rochester, NY; Denver, two days by wagon train. On Thursday, Press Day, I wandered around getting the layout of the ranch. Some of the larger rooms in the Conference Center were up and running and I wandered into Red Rocks 2 where I found two models of Sigma Acoustics speakers from Italy driven by two different AGD monoblocks — the aforementioned Vivace and the new Audion model that looked like it might be an honest-to-god real tube amp. It wasn't. The brushed aluminum version was attractive but the polished aluminum version on silent display at the side of the room was stunning. Was it just my fetish for tubes and chrome? At half the price of the Vivace, the diminutive Audion puts out 85 Watts per side into 8 Ohms, 170 Watts into 4 Ohms and again, is steady down to 2 Ohms. A smaller power supply permitted a smaller chassis, yet could still output more than 30A of current on peaks. Adapting the aesthetic design cues of tube amplifiers allowed for a compact design and sturdy protection for the exposed tube. I let Alberto know right away I was very interested in reviewing this new amp.

Over the course of the show each speaker was driven by each amp. I can't say I heard all the combinations, but I can tell you each visit was very impressive — another Best Room at RMAF. Alberto had worked with Aldo Zaninello, founder and managing director of Extreme Audio and designer of the company's Sigma Acoustics loudspeakers at High End, Munich, in 2019 where his ‘modest' amps drove the Sigma Orchestra 2.6 speakers (€41,000 plus VAT). Aldo's efficient speaker designs can be used with almost any amp but his main reference amps are huge Mark Levinson monoblocks. The Sigma speakers at RMAF were the large Maat Vector XAC (€151,500 plus VAT) and the smaller Orchestra 2.3 (€27,800 plus VAT). They have representation in major markets around the world, including New York and Los Angeles.

Also in the rig at RMAF was the prototype of AGD's new Andante preamp/DAC with four analog inputs, built-in phono, 32/384 processing with AES, optical, Bluetooth and LAN inputs and three sets of outputs for tri-amp'ing loudspeakers. Look for this at AXPONA in the spring (2020). All of this is making for an auspicious entre into the high-end for Alberto Guerra who comes to this industry from the power electronics field. All indications are that he has done his homework. I parted with a handshake with Aldo and Alberto, and looked forward to hearing The Audion later in the fall. In retrospect, I should have spent more time talking with Aldo, too. Hopefully, I'll have another opportunity in the future.

The FedEx driver left his truck in the street and ran up the driveway with a flight case in hand. "Please don't drop it" ran through my head as I stepped outside to sign for delivery. The heavy duty design of the case plus the tight foam packing around the amps suggested they might easily have survived a drop of several feet. The packaging was exceptionally well designed, right down to a pair of white gloves and a nicely constructed pair of power cords with solid copper spades. I was still in the middle of my Rocky Mountain report, but I fired them up and took a listen.

They were pretty spectacular right out of the case and remained so for several days after being left on continuously. Don't these things burn in, Alberto? He explained that the semiconductors don't have any significant aging characteristics and since there is no variation of bias nor a huge variation in temperature, they were not likely to improve. Electrolytic capacitors will change a bit, but there are only two in the entire amp... and given the 94% efficiency of the amp, it only gets slightly warm, so not much change is likely to happen with them, either. It runs so cool the chassis does not need ventilation, though there is a slight opening around the tube socket. Even the glass tube is only slightly warm. And with the small footprint, there is no need to worry about your cat napping on them. They are a great choice if you live in warm climates or if your air-tight listening room suffers from the build-up of heat.

The Audion has both single ended and XLR (balanced) inputs, totally independent, that feed two identical Op-Amps (LM4562) with ultra-low noise and a fast slew rate. All the resistors are ultra-high precision metal foil type. The input impedance is 40kOhm, which should be suitable for most preamps or DACs with variable output if you wish to run direct to the amps. Since the Coincident preamp only has single ended outputs, I was only able to use my two-meter Synergistic Research Foundation interconnects with the amp. After using the amps for a week or so I recognized that it seems to take very little time to warm up. What little improvement occurred within a half hour was most likely my tube preamp continuing to settle in. Basically, it's "good to go" from the minute you turn it on. Even leaving it on continuously for days did not seem to make a difference.

Form Factor Considerations
The monoblock is heavy enough at 6 pounds 14 ounces (3.11 kgs.) that most power cords will not pull it off a shelf. The rubber feet are reasonably sticky and will keep it from sliding. Both RCA and XLR interconnects attach straight into the back of the amp as well. The speaker cables, however attach to the binding posts on the top deck of the amp. Banana plug connectors will require the cables to shoot straight up before arching toward the speaker — something to consider if you plan on placing the amps on a lower shelf. But the amps are so fetching you will probably want to put them out into the open where they can be seen. You will probably want to restrict the use of banana connectors to lighter weight speaker cables for the same reason.

There is plenty of room to attach speaker cables with wide spade connecters, but there is no hole in the threaded post for bare wire ends. There are two flat notches in the side of the post where 6mm (1/4") wide spade connectors will be firmly held in place with the cables aimed straight to the rear of the amp. This is but one example of the attention to detail that has gone into these amps. The binding posts themselves (WBT) are very sturdy and feel like they are anchored in concrete or welded to the chassis, though obviously not. Simply put, built like a tank. And made in the USA, though some parts are sourced off-shore as you would expect in this industry.

I'm a big fan of Synergistic Research's fuses so I ordered a pair of 6.3A small size Orange fuses to see if they would work their typical magic. Right out of the box there was a noticeable improvement in transparency and focus, but once into the second song the fuses began their typical sound quality dance. I set my Sony CD player/transport to "repeat" and let it roll for a few days. But the swap was not without some drama. (The manufacturer notes that in retrospect, Rick should have read the user manual where all is described with details, so it would have been simple.)

The entire input unit with IEC input/power switch/fuse-holder makes for a very crowded design. You have to disconnect the power cord in order to access the fuse holder (a good safety feature), but also the collar of most power cords will partially over hang the on-off switch. Everything functions fine, but when activating the power switch your finger will touch the power cord, which feels a little awkward. This is certainly not a deal breaker in my opinion. The amp has too many good things going for it.

Alberto explained the unit is from TE Connectivity in Japan, one of the largest manufacturers of these devices in the world. It is the top model in their Medical Grade series with tight specs for ground leakage and EMI shielding. It is compatible with 5x20 or 6x30 fuse sizes and it will work with either one or two fuses in series. Furthermore, by flipping it over it can be used for either 120V or 220V. A little jumper is used if using only one fuse. I suggest you change the fuse on only one amp at a time, keeping the other amp for reference in case you don't load the fuse holder correctly. The good news is the Orange Fuses really work their magic. Given they are only 4% of the cost of the amplifiers, it is a very worthwhile upgrade, not unlike putting high quality tires on your car.

Speaking up upgrades, I used a Symposium Acoustics Svelte Shelf placed on top of one of my tube monoblocks as an amp stand which offers a bit of improvement from past experience with it. Eventually, curiosity got the best of me and I tried a trio of Synergistic Research MiG dome footers beneath each monoblock and eked out a bit more performance. The chassis is so small and rigid it has little propensity for transmitting internally or externally generated vibrations. The Orange Fuses were the biggest bang for the buck in my experience with these amps. But the cart is getting ahead of the horse here. Let's move on to the changes The Audion brought to my system.

The Sound Dimension
I've been a tube guy for most of my audiophile life and likewise as a youth before the transistor was invented. Slightly warm, holographic sound has been a high priority for me, though it was the increase in resolution that drew me into high-end audio in the first place. Recently I reviewed a Legacy PowerBloc 2 Class D stereo amp with 325 Wpc into 8 Ohms that I thought might make a huge difference for me. While it was a good amp, well-built and a great value for under $1800, I wasn't willing to give up the glorious tonal color I had with my tube amps. Using ICEpower, all the extra watts and tighter bass didn't outweigh the engaging color I was getting from the parallel 300B tubes in Eddie Wong's monoblocks. As is often said, the first watt is the most important one. It sets the tone for the ones that follow.

The Audion brought nearly as much tonal color to the midrange, but surpassed the tonal color of the bass and treble that I was getting from the 300B tubes. It's no secret the 300B is soft in the bass and rolls off in the treble. In spite of the fact that The Audion had a smaller power transformer than its big brother, it still had a much higher damping factor (> 1000) than any tube amp I know of. This was immediately noticeable in the bass which had much higher resolution, greater tonal color and greater impact in my chest than I thought possible from such a small amp. At a distance of 9' from the speakers, it didn't pound me, but I could feel it in my chest and in the slight tingling vibration of the arms of my leather recliner. I get the same physical sensations from my tube amps, both of which have very substantial power supplies, but not the tight focus that comes with The Audion.

In the treble, the greater resolution provided more air and a sweeter sound, particularly from string instruments and woodwinds that likewise resulted in greater tonal color. In spite of a very small loss of color in the midrange, relative to the 300B tubes, the large gains in the bass and treble resulted in a net gain for the entire audible spectrum. Moreover, the speakers seemed to gain in bandwidth. The top end was far more extended than before. The bass, on the other hand, did not seem to go much deeper than before, but it became much more focused — right down to the lower limit of the speaker at 33Hz where it cleanly dropped off, leaving no muddy residue below that point. Credit the very high damping factor. Thinking back to RMAF, I wondered how The Audion would perform with a true full-range speaker that went all the way down to 20Hz, or what my Kharma would sound like if they were supplemented with a pair of fine subwoofers.

Recall I mentioned the fast rise time of the GaNfets? Rim shots and most other notes begin Right Now!  And with no over-ringing. Likewise the high frequency of notes in the treble are more clearly resolved and sound a lot more like real instruments. With sustained notes anywhere in the spectrum, they come across as musical Hz, not musical hash. Clean and pure. And as usually happens (but not always) with an increase in resolution, there is greater transparency as if more light was cast upon the performers. In particular, the extreme sides of the soundscape and the entire back edge were much better lit than I can ever remember. Back-up singers far to the side or far to the rear of the stage were clearly delineated. The refrain in Bruce Springsteen's 57 Channels was clearer than all but one time with a very expensive digital cable I couldn't afford. The Audion differentiated the three female voices of Wilson Phillips covering Elton John's Daniel with more separation and tonal color than I've ever heard. Likewise, the cymbals in that cut were beautifully portrayed revealing real shimmer without hash.

The Soundscape
The increased resolution combined with the lowered noise floor of The Audion made the soundstage recede slightly from where it normally resides, yet I could hear the music and lyrics more clearly. The soundstage scaled appropriately as the volume was turned down…or up. I noticed that I was more prone to adjusting the volume slightly to accommodate the varying volume levels of different CDs — probably because the increased resolution revealed the proximity of the soundstage more clearly. With my speakers on the long wall of the room, quite far from the side walls, it is not unusual to experience a very wide soundscape. Perhaps it was the additional illumination created by the excellent transparency that gave more presence to the perimeter of the soundscape that made the stage width seem even wider and the far reaches across the back so much more engaging.

I don't normally listen to a lot of orchestral music, but when I did, I could 'see' and hear the entire orchestra with appropriate width and depth. The soundscape was not quite as deep as with my tube monoblocks, probably because the back of the stage was so well lit, rather than fading into darkness like I get with the 300B or 845 tubes. While I noticed the slight foreshortening of the soundscape, I didn't miss it because there was so much other good stuff going on to enjoy. In the rapid piano playing in Mozart's 8^th piano concerto every note could be clearly heard.

Part of the excellent soundscape is due to the fact that The Audion is a monoblock amplifier. They frequently do the soundscaping thing better than stereo amplifiers. Fanatics in Europe, more so than the USA, take the separation of channels even further — to the front ends and preamplifiers as well, but you pay dearly for this degree of obsession. Pinpoint imaging is not a top priority for me, but I should comment that the musicians were clearly defined with believable body and size, though not a geometric pinpoint. Combine those believable proportions with the high resolution and tonal color of The Audion and you achieve a very good sense of physicality, of real musicians. Whether you are in the venue of the recording, or the musicians are in the room with you at home will depend upon your room and the recording itself.

At moderate levels, The Audion has the ability to do either. With a 6000 cubic foot room that opens into another large room, I use a mid-field listening triangle about 9' on each side. I normally listen at levels with peaks from 88 to 93dB at the chair and never wanted for more power from The Audion. If you are a headbanger or have a very large room and like your music at concert hall volume from 5^th row center, you will want more sensitive speakers than my Kharma. Or you can hang in there for a more powerful AGD that's in the works. Keep saving while you wait as it will likely be more expensive than the Vivace.

Value & Aesthetic
I normally consider these as separate topics but with the polished version they are inextricably connected. In polished form The Audion looks and performs like it should cost twice the price, and even then, I could be underestimating what the market might bare. Opt for the flat finish and you may regret it ten or twenty years down the line when you want something with more class. It's good enough that you will likely keep it that long unless the size of your room or the demands of your speakers changes dramatically at some point. That's how value really kicks in — when you spend more for high quality and then hop off the merry-go-round of audiophile upgrading by hanging on to a design that is destined to become a classic.

The amps are also easy to place near your speakers, so there's possibly money to be saved by going with short speaker cables and longer interconnects. The accompanying power cords were very decent, though my much more expensive reference cables performed a bit better. More value added. Aesthetically, the orange LED seem brighter than necessary in daylight, but it's warm presence while listening in the dark was just right. Go figure. And one final benefit, I can crank up the volume and enjoy music throughout the house as ambient music all day long without worrying about the cost of expensive vacuum tubes. This could be a change in lifestyle.

Summary
When I first discovered high-end audio there was a fairly wide separation of the tube and solid-state camps. It was pretty easy to distinguish one from the other and I fell in line with the tube guys. It was in my DNA from an early age. Today, along with advances in speaker design, we've reached a level of sound quality at the upper reaches of this industry where I really don't care whether an amp is tube based or solid-state. The music is simply so good. And partly I don't care because I can't afford the gear at that high level. While The Audion is not inexpensive, it breaks through what for many is a megabuck financial threshold making it a lot more accessible than most amps of this quality.

The Audion gives us upper echelon resolution without etching or glare that promotes all-day listening without strain or pain. As with the loom of Synergistic Research Foundation cables that came before the Audion, I am once again amazed at the untapped quality that has emerged from the Kharma speakers I've used since 2003. The Audion takes my system up into the level of Best Rooms I hear at shows without doubt or question. It is not a muscle amp. It aims for quality, not quantity. Combined with reasonable gear in a reasonably sized room, it should be an excellent driver for a wide variety of speakers. The small size and touch of glamour these polished beauties bring to a room might even endear your significant other to your passion for music.

How often do you hear about a tube guy converting to solid-state? Much less a reviewer with SET tube amps switching to a Class D amp? Long after this review has drifted into the archives, I will pull an LP, one of thousands, off my shelf and be reminded that Elvis has not left the building; nor has this gem of an amplifier. AM sending a check to the manufacturer, I bought the review samples. With AGD's application of the GaNfet, Class D has reached the upper echelon of high-end audio.

Welcome to the club, Mr. Guerra, and please, keep up the great work!

Specifications
Type: GaNTube monoblock amplifier
Output Power: 85 Watts @ 8 Ohms, 170 Watts @ 4 Ohms (>30A max current capability)
Frequency Response: 5Hz to 100kHz (+/-3dB)
THD+N: <0.005%
Input Impedance: 40kOhm (600 Ohm upon request)
Noise: < -130dB (A-weighted)
Gallium Nitride MOSFET based Power stage
Audio Power Stage Fully integrated in Glass Tube
GaNTube PWM Frequency: 400kHz
Size: 5.5 x 9" x 7.675" (WxDxH) 
Weight: 6 lbs. 4 oz.
Warranty: Three years parts and labor
Price: $6800 per pair in in mat finish, and $7500 per pair in polished finish.

Company Information
AGD Productions
Los Angeles, California
Website: www.AGDproduction.com