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