AGD GaNTube88KT MKIII

Introduction

My AGD Audion monoblock amplifiers just received an upgrade to the GaNTube88KT MkIII. Let's see what differences it brings to the table and whether it is a worthwhile upgrade for existing owners.

Description

AGD builds their amplification stage into a glass envelope. While visually looking like a vacuum tube, they are solid-state devices. Some people have criticised AGD for this move. I found it visually appealing and an interesting talking point. With the introduction of new "tube" variants, AGD users are now able to upgrade their amplifiers without too much hassle. You could swap the "tube" in under 5 minutes per side, with most of the time spent undoing the hex screws to remove the protective cage for my Audion. This is not necessary, but gives my large fingers more room to work.

The MkIII has been two years in the making, and AGD claims that the PWM stage and output filter have been redesigned with more advanced materials to deliver reduced distortion, lowered noise, higher bandwidth and faster response times. 

Class-D amplifiers require a low-pass filter to remove high-frequency circuit noise. Poor filtering designs result in a loss of high-frequency detail and air. According to AGD, the new filter results in flat response up to 60KHz.  

Output power has been increased to 250W at 4 ohms, and with the Audion, 200W at 4 ohms, due to limitation of the power supply of the Audion. In comparison, the original "tube" delivered 170W at 4 ohms.

Sound Quality

Despite the increase in power rating, there is no noticeable increase in gain moving to the MkIII. The tonal balance remains close to the original, although there is a noticeable improvement in speed and neutrality. Bass quality immediately hits you with more power and articulation. Low frequency notes simply go deeper and with more detail. 

On the midrange and high-frequencies, there is better vocal refinement, with an improved sense of air. Placement of voices and instruments are also improved, with better separation and dimensionality.

In tube terms, the improvements are similar to a change from KT88 to KT120 tubes. It's possible that some listeners may prefer the softer presentation of the original tube, but most would prefer the MkIII. 

Conclusion

The improvements are not on a subtle level and are on par with the sonic gains associated with moving one model up the product line. This makes the MkIII an easy recommendation for AGD customers. My only criticism is that AGD should make available a trade-in program for customers to help defray the cost of the upgrade.  

Price : USD 1,500 per pair

AGD Audion Monoblock Power Amplifier

Introduction

AGD Productions Inc is the new kid on the high-end audio block. The brainchild of Alberto Guerra, AGD Productions Inc produces products that are distinctive and different from the competition.

For one, their amplifiers use their proprietary GaNTube™ technology. A friend of mine mentioned, "It looks like a tube, lights up like a tube, and sounds like a tube". The photo of the GaNTube™ below shows that a transistor based circuit housed in a vacuum tube like envelope. From the octal base, to the getter flashing on top, this looks like a typical 6550 or KT88 tube.

The GaNTube™ is a class D circuit, utilising Gallium Nitride MOSFET transistors in lieu of conventional silicon transistors. Gallium Nitride is being touted as the next big thing in semiconductor manufacturing, boasting superior performance in more compact packages. They are superior in terms of power efficiency, thermal stability, RF production and immunity. 

Alberto Guerra enjoyed a long and illustrious career in companies like Infineon and more than knows his way around Gallium Nitride technology, holding ten patents to his name (including two in Gallium Nitride know-how).

Description

The Audion comes in a really big Pelican case. Opening the case reveals the the pair of monoblocks, product literature and a pair of power cords. The amplifiers are compact and light at 2.5 kg each. In fact, the Pelican case feels heavier than the amplifier. 

Finishing is of high quality, with a solid indestructible feel. You can opt for the brushed finish, or a chrome finish for a premium. My review sample came with the brushed finish. The company logo is engraved into the front panel, while all inputs and the power inlet are located at the rear. The excellent speaker binding posts (a pair of WBT Nexgen 5-way posts) are located on the top of the amplifier, behind the GaNTube™. If you are using spade terminated speaker cables, this all fits very nicely. However, if you are using banana plug terminations like me, your cables will arch gracefully (like my flexible speaker cables), or suspend your Audion amplifier in mid-air in a worst-case scenario.

The power switch is located directly above the IEC inlet and will be partially blocked by monstrous power plugs that ship with any serious garden hose. Otherwise operation is event-free. The GaNTube™ glows orange like a vacuum tube except very little heat is produced. I demonstrated this to a visiting audiophile by resting my finger on the GaNTube™ in the middle of a listening session. No start-up noises or power-down thumps - excellent manners for this house guest. 

The Audion packs plenty of power, delivering 85 WPC into 8 ohms and 170 WPC into 4 ohms. It can deliver more than 30A of current which should be more than enough for most of the speakers out there in the wild. The input impedance of both the RCA and XLR input is 40 kohms (600 ohm inputs can be custom ordered). Noise is an astonishingly low -130db. The GaNTube™ switches at a frequency of 400 kHz.

 

I tried the Audion with three DACs with digital volume control (the Chord Dave, Totaldac D-1 Six and Antelope Audio Zodiac Platinum DAC). I also tried using a Music First Audio TVC preamp. Although the specifications do not specify the input sensitivity / gain of the Audion, it is definitely quite high. All three DACs were being used between -30db to -20db. In the case of a DAC with digital volume control, that is sufficient attenuation to potentially result in resolution loss. If you are using an active preamp with high amounts of gain, you have been warned ! In fact, this is one of the very few power amplifiers I've used that sound really good driven directly from the source. Save your pennies by skipping the preamp ! Another noteworthy point is that Audion sounds good through both the RCA and XLR input - no worries if your source is single-ended only.

Sound Quality

Let's get this out of the way first - Class D amplifiers get a bad rap from audiophiles. Conventional wisdom is that Class D amplifiers are sterile and lifeless. I have owned and auditioned enough Class D amplifiers to understand their appeal and their strengths. Many years ago, I bought a pair of monoblock amplifiers from a Japanese company called Flying Mole. They are no longer in business, but the product showed great promise. I have also owned a number of Class T amps (i.e. based on the Tripath chip), and amplifiers with both B&O ICEPower and Hypex modules. Each generation of module showed steady improvement, and a number were of high enough quality to challenge traditional amplifier designs.

The Audion need not make any excuses for itself. The sound quality easily surpasses most traditional amplifier designs and can even be considered as a serious challenger to the top amplifiers on the market. 

First up is the bass authority you get from the Audion. Class D amplifiers typically have superb control over your woofers. In some cases, you get a tight bottom-end that seems artificial with a lack of shading or texture. The Audion breathes freely here - as an example, double bass notes flow with timbre and life. The bass has just the right amount of wetness for me, although I did feel that there was a slight midbass emphasis, which resulted in a weightier and warmer tone.

The midrange has an inner glow quality that good single-ended triode amplifiers possess. However, this glow is even-handed and avoids the thick luscious tone that some tube amplifiers aim for. Some equipment smooth over the midrange to portray a more "musical" tone, but the Audion retains plenty of microdetail. 

The Audion's high-frequency performance must have delivered the greatest surprise during my review experience. Even the best class D modules I have heard (with the exception of the Orchard Audio BOSC - a story for another day) subtly reduce the top-end air in the recordings. While they do not by any means sound dull or rolled-off, you could sense a slight reduction in the scale of acoustic space. I always assumed that this was a necessary evil resulting from the low-pass filter required in class D designs to filter out ultrasonic noise. The Audion come through clear and extended. Neither is there any glare or harshness in the reproduction - cymbals crash and bells ring in a clear and extended manner, with a firm but crisp tone. 

Solid state amplifiers excel in staging precision but often cannot match tube amplifiers in dimensionality - the acoustic space around voices and instruments, and the perception of depth and height. The Audion could very well have been of vacuum tube pedigree in this regard, delivering convincing reproductions of each voice and instrument in the recording mix. Marry this with solid state speed and low frequency control, compactness and lack of heat - you truly get the best of both worlds here ! 

Prior to my experience with the Audion, discussions about Class D amplifiers with friends have always been caveated to a degree, e.g. "They deliver a lot of clean power for the price and are very accurate, but you really need a good preamplifier to flesh out the tone and complete the picture.", or "They really deliver bang for the buck, but if you spend a lot more, you can get even higher sonic performance." 

My caveats here are altogether different. Firstly, the high amounts of gain requires some care in matching with preamplifiers and sources. Secondly, the Audion is not affordable although it delivers exceptional sound quality for the price. The price tag puts it out of reach of most audiophiles but quality is never cheap. 

You could also make the argument that the Audion is not neutral. It isn't and to me it was almost certainly a deliberate design choice. Instead, it chose to be musical and delicate, while having the speed, power and control to bring realism to large-scale works. You can now have your cake and eat it ! 

Conclusion

The Audion is a truly revolutionary product. I understand that AGD already has several different GaNTube™ designs in the making, including a higher powered version, and a lower powered one for headamp use. The new modules may be installed in place of the current GaNTube™, which shows that the socketed GaNTube™ is not merely a whimsical fashion choice. 

Keep you eye on AGD, this is a truly special product that will redefine your notions of Class D and solid state technology - Highly Recommended.

This review was made possible with the kind assistance of Horizon Acoustics, sole distributor of AGD Productions Inc in Singapore. 

AGD Audion Monoblock Power Amplifier

Price : SGD 12,800

Horizon Acoustics

1 Pemimpin Drive

#08-11, One Pemipin

Singapore 576151

http://www.horizonacoustics.com