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AGD Production Vivace GaNTube Monoblock Amplifiers

11-06-2018 | By Pete Davey | Issue 100

AGD Production Vivace GaNTube Monoblock Amplifiers

I hear this term thrown around loosely... "disruptive product," sometimes appropriately used... however in this case, we have a winner.

I've been on a mission lately, unintentional as it may seem, to be reviewing Class-D based amplifiers. Talk about a dirty word. I've had so many in an out of here, my head is spinning. No idea why that is happening, but I'm having a blast nonetheless. But, I'll be honest. Most of the time, it's a similar sound. Sometimes a little more here and a little less there, but this time I've got something here that truly redefines Class D. In fact, I wish there was a way to reclassify its design topology just so that it didn't have to be defined as Class D, because of how many amazing boxes it ticks.

First let's get over the design aesthetic. I've heard so many crap talkers say "uh, that's not a real tube, wtf is this guy doing?" Well, hate to break it to you snobby audiophiles (wink), but it is a tube. It may not be a traditional triode tube, but it's a tube. Stuffed with a completely custom module made from Gallium Nitride! I mean, the designer Alberto didn't just have to create his amplifier from the ground up, but he also went to level 11 by going with a Gallium Nitride-based transistor (vs. the normal silicon style). Why you ask? Because he's a madman! Okay, honestly, he's been one of the most pleasant designers I've ever spoken with. He truly knows how to make another person question their own intelligence by the wisdom he has with regards to design with electronics and power supplies in general.

Alberto Guerra has a rich background in designing test equipment for other industries where consistency and accuracy is key. This is where he got the idea of using Gallium Nitride in his amplifier module—he figured why not use something different, something more powerful, accurate, and of course more complicated to design around. He has trademarked his technology "GaNTube" where it truly creates a one of a kind unique sound that is just impossible to compare it with anything.

Going back to Class D in general, most of the time it's either something from B&O using ICEpower, or something from Hypex (UCD or NCore). Such modules are used so that one can mod to their liking by inserting a custom power supply (switching or linear, dealer's choice) and also a custom input board / buffer circuit to tailor the sound even more. But when you strip that all away, you are still left with the choice of ICE or Hypex, where one cannot just run away from that typical sound signature. Don't get me wrong, I have heard some amazing Hypex or ICE based designs, but all of them can at times get a bit ear fatiguing in a sense. I don't know if it's inherent distortion, or what, but it's inevitable. I've yet to take home a Class D based amp permanently (using Hypex or ICE). Catch my drift?

Also, with such design, for some reason also comes an aesthetic compromise. It's usually a boring rectangular or square box, with a power button and connectors on the rear. Sometimes you'll see a manufacturer throw a sticker on it saying "powered by Hypex" or "powered by ICE." Sometimes they won't say it at all until you open the lid on the thing, but they're usually very utilitarian in design. Sorry guys, but AGD has taken it to another level. Not only is this thing very well designed on the inside, but the outside is a keen match. The top of the unit is clear so one can peek inside. The interior of the case has Amber LED lighting embedded everywhere to give it a beautiful warm "glow." This design aesthetic carries all the way into the GaNTube making it appear as if it's a triode from afar. The obvious giveaway that it's solid-state is that there are no big honking / buzzing (sorry) transformers. Sorry Triode vacuum tube purists, but I say this thing is dead sexy, and dead quiet.

Another really trick design aspect is that the GaNTube is truly housed in a traditional 6550-style glass tube with pins and all, so one can expect that there will be different sounding GaNTubes released in the near future so one can "roll their own." Talk about neat! I am excited to see what comes with this new technology.

AGD Production Vivace GaNTube Monoblock Amplifiers

Regarding the design itself and power supply specifics, I'll turn to the information provided on AGD's website:

With the seamless ability to drive any loudspeakers, 200W of power, 48,000µF of super audio grade capacitor reservoir, and the fastest slew-rate, the GaNTube™ Technology delivers the purest sonic experience. 

Thanks to the Gallium-Nitride power stage intrinsic characteristics, the virtually stray-inductance free package, and a state of the art layout of the power module, the rise time and fall time of the Vivace's GaNTube™ power stage are fully symmetrical at ~15ns. The output waveform at the switching node of the Gallium-Nitride power stage (pre-LC filter) is completely oscillation free even with a slew rate of 3700V/µs!

This oscilloscope snap-shot of the output power stage half-bridge switching node, is a dramatic evidence of the tremendous difference in switching speed between the Gallium-Nitride Power MOSFET and the state of the art Silicon Power MOSFET equivalent.

The combination of low noise design technique implemented and the best practice for the internal board layout, the RF quality BNC connectors for the analog signals, are the key contributors of the excellent noise floor of the Vivace Monoblocks and extremely low distortion.

I love putting amps to a true test to see what sort of speakers they will drive and how they will sound. During this review, I have had several sets of speakers here. I've had difficult to drive (low impedance) ribbon speakers which require gobs of current and are a resistive load. I've had ESL panels which are a swinging paradise of impedance loads, and also dynamic speakers. I was truly amazed at how well it worked in all scenarios. Even on my friend's hefty Apogee Full Range speakers, they played quite well! In fact, they really blew the socks off of my friend's setup where he normally drives his midrange / tweeter ribbons with a huge NAT Single Ended Triode amplifier! We were ready for a stark difference but it was impossible to tell, the system remained detailed yet warm and rich, which is what most people are wanting out of a solid-state amplifier that they can get with a tube amplifier quite easily (minus the entire mess with Triode tube amplifiers in general). That was a lot of fun doing that—it gave me positive affirmation that Alberto was on the right track with these amps.

Okay. Music time!

I just got hold of some really cool albums. First on the list is Richard Devine's Sort\Lave. Richard Devine is one of the old "pioneers" of the electronica era, and this album is no slouch. Chock full of dynamics and instruments which really gave me pause several times. Sometimes listening to such music can be fatiguing, depending on the ancillary equipment used, but I heard no nasty ice-picky scratching here as provided by some other amplifiers. Nothing but very clean loud dynamics.

Moving over to something a bit more classical, Max Richter's latest soundtrack for the movie White Boy Rick is quite a moving piece (as with most of his music). If you've not heard of Max Richter, don't wait any longer. Most likely you have heard his stuff from movie / TV soundtracks. One of his most recent albums entitled Sleep is an 8-hour set designed for you to play back during a sleep session. Quite lovely. Chock full of live instruments and singers, this one is quite nice and a perfect match for the GaNTube sound. I really felt like I was there during a live recording session! Very warm and rich sounds akin to a SET tube amplifier, but with more dynamics and breadth.

All in all, I can't say enough good things about these amplifiers. While auditioning them, I couldn't wait to share my findings with you. I truly believe that these are one of those disruptive products that can change one's mind about how much better high-end audio can get—which is rare these days. I urge you to check these amplifiers out. Especially if you are really into the tube sound but don't want to fuss with tubes going bad and high power bills. If you're like me and you are a music addict, your system is on all day and it's quite nice when you can simply hit play (using Roon of course!) without the entire song and dance warm-up process.

Vivace GaNTube Monoblock Amplifiers

Retail: US $15,000/set.

AGD Production