New Generation Class D - AGD Audion Mkiii upgrade


I have always had a preference for horn-loaded loudspeakers which, whilst typically easy to drive, can be quite revealing (good/bad) of any changes in the system. I am running Avantgarde Duo’s and have until now always preferred valve amplifiers for their mid-range and lack of fatigue.

I have heard a number of Class D amplifiers and one or two have sounded pretty good but a bit lean compared to valves. Tha changed when I purchased a pair of AGD Audion Mkii amplifiers. The Audions have an almost valve-like mid-range but with a wonderfully transparent top end and great sound-staging. It’s always been difficult to get really convincing bass with my Avantgarde’s because if you increase the bass level the low frequencies can sound detached from the glorious mids/highs. This changed with the Audions as the bass is faster, more dynamic and just overall more satisfying.

These compact amplifiers have what appears to be a valve for each amplifier. This ‘valve’ glows red and I rather like the effect. I did think this was a bit of a gimmick at first but it contains a Gallium Nitride MOSFET power stage. However, this ‘GAN-Tube’ means that if an improvement is developed you can just swap the tubes for the new version. That is exactly what I have done as AGD have launched a Mkiii ‘GAN-Tube.

I was extremely happy with my Mkii Audions and wasn’t sure what to expect with the Mkiii tubes. But as audiophiles it’s difficult to resist an upgrade. The new tubes were fitted in under 5 minutes. I’ve found most components need time to warm-up and ‘burn-in’ so wasn’t expecting too much initially. However, it immediately became apparent that, even at very low volume, there was more detail. I pumped up the volume and was astounded by the wider soundstage which extended beyond the speakers and allowed you to pick out instruments and vocals even clearer. This is something that I’ve found difficult to achieve with Avantgarde’s and I didn’t have with my previous OTL amp. Dynamics are a strength with horns and the Audions really produce a ‘live’ sound, quite startling at times. I’m not great at describing all the audiophile things but would just say that these amps make the system sound so enjoyable and exciting to listen to. They are the best by far that I’ve had in my system.

I know some people will have a hesitation over Class D amps (like I did) but I really think this next generation amps like the AGD Audions will become more and more popular once people get the chance to hear them.

rocketiii

@tonnesen 

Any update on your experience? Were you also able to try the Atmasphere class D?

I have the MK III for about 2 weeks now and am just impressed at the clarity and sound they produce. Immersive is a good description. I am thoroughly impressed and satisfied with these. 

@atmasphere I understand but before International Rectifier got bought by Infineon, they were working on an audio solution.  When that project got scrapped I believe Alberto bought all of the product produced to that point and began the process of designing and building his amplifiers from that stock--which had been produced with audio as the end game,

@atmasphere 

Sorry, but what you are stating may be applicable to the rest of the GaN MOSFET but that is not correct for the device we use in the Audion GaNTube88KT and I will be more than happy to describe to you why.

Without boring anyone with complex terms, in short, the reason is simple.

Since you know very well the difference between fixed D% (i.e Buck or Boost converter) and variable D% (i.e CLASS-D) operations, symmetrical HB and asymmetrical HB configurations, and among other things how important the stray inductance of the switching pair at the switching node is (we switch our power stages at ~800KHz but we could go much higher...), you should easily derive which parameters and physical elements of a semiconductor device (the 3 terminals switch) need to be optimized to make it operate at best in each different topology with the ultimate goal to obtain not just the best efficiency....but in our case, a great sound...and these parameters are not the same. I assure you ;)