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After 50 years, I have finally found my destination amps... AGD Audions!

I will never forget my first system. When I went away to college I bought a $199 Pacific Stereo special-Niko receiver, Lenco TT and Quadraflex speakers. That was 1971.I don't know how many upgrades I have done since. But, by far, finding the "right" amp has been the quest for the holy grail. And after decades of different SETs, finding a SS amp that will satisfy a SET guy has been problematic... until now. I was first inspired by Forum member's rave comments. Then looking at the reviewers, I found the unique and consistent phrase "best regardless of price". With the end users and reviewers all agreeing, I decided to try a pair of AGD Audions.
Within minutes, I understood what everyone was saying. Now, after about a month of listening, I am convinced that I have indeed found the "holy grail". A SS amp that completely satisfies a SET guy... and more. I am thrilled daily by the way the Audions grab me. Now, it is no longer merely listening. It is being enveloped by a sound that opens a window into the musician's hearts and souls. They do so with an incredible lack of distortion, detail and transparency. I have never heard anything like it. Excuse what appears to be hyperbole but now hearing the Audion mono blocks I am overcome with the emotion I hear and emotion I feel.
I have come to understand that AGD Class D amps are indeed unique. The designer, Alberto Guerra, has a long background in integrated circuit development holding 10 patents including those for the MOSFETs used in AGD amps. The galium nitride modules are the only, and patented, GaNs designed specifically for Audio. All other GaNs were designed for battery chargers, radar or lidar, etc. Alberto, like Nelson Pass and SITs, owns all these GaNs made.
These amps are extremely fast. Their switching frequency is far beyond other Class D amps. AGD amps sound organic and natural with great realism like a SET but with liquidity and slam. The definition and immediacy puts them above any SET I have heard. The “tube” on top of AGD amps is a kind of tribute to the original 1906 Audion tube even though they are not vacuum tubes. They do however contain the full output stages. This contributes to heat dissipation and is a clever way to make the amps good for future upgrades. No need to ever buy a “new and improved” model. Just replace the tube. Alberto has issued a Mark II tube which is already used in his new amps and available for older.
Some would question the unique cosmetic design but once they are heard they become very beautiful. And, personally, I find them very attractive beyond the normal metal box. And the attention to fit and finish is of a high level including two excellent power cords and flight cases for shipping.
AGD amps are my final, destination amps. I am thrilled daily. My only considered upgrade would be to the top line Gran Vivaces.
mglik
tmcclintock
35 posts
 
atmasphere06-15-2021 8:01am To be clear, Alberto does share a patent on GaNFETs (US8847408B2). And the modules he makes are of course designed for audio. But it appears to me that you've conflated the modules with the GaNFETs themselves, and the latter cannot be specifically designed for audio. This is because class D are switching circuits which have a lot in common with switch mode power supplies and the like. Put another way: there isn't a way that the device can be specialized for an audio switching application where it will not also benefit a switching power supply or battery charger in exactly the same way.

I believe mglik's information comes from a 6Moons review or maybe direct conversation with Alberto.  From 6Moons quoting Alberto:
"...The device I use was developed very specifically for class
D audio, *not* for power supplies, low-voltage points of load or RF circuits. Hence the key figures of merit for the device were optimized for best performance within specific voltage ranges, frequencies and current..."
and
"...On why nobody else can use his KT88 GaN, it's like with Nelson Pass' proprietary static induction transitor.  Alberto acquired the entire remaining lot..."
atmasphere's avatar
atmasphere
11,807 posts
 
Not sure I understand. If Alberto does hold a patent on the GaNFETs, are not his modules then uniquely designed and one of a kind. (other than the “tube” enclosure) Surely this is the case for much or some central part of the design? Are you saying that AGD are not unlike other GaN based amps?
I'm sure the modules are uniquely designed! That to me is really obvious. But at the same time the circuit design is probably very similar to other class D self-oscillating circuits. It would of course differ in how the circuit is laid out and what parts are used. All class D designers are faced with the same circumstances in this regard.

The idea of the output device being designed specifically for audio sounds a bit like hype to me. GaNFETs are desirable for three reasons- the speed of them, they low resistance ON state and the reverse conduction characteristic. While these things benefit class D amps, they also benefit other switching circuits as well.
mglik OP
908 posts
 
What parts are used specifically the GaNFET which is patented. As stated, like Nelson Pass and the SITs. Although I don’t believe Nelson has a patent on SITs.
rh67
307 posts
 
mglik

Nice to read when someone has found something in audio that is truly special especially when it comes to someone with your experience it lends credence to what you say.

I met Alberto at THE SHOW this last weekend, he is a very intelligent man yet humble and in many ways reminds me of Nelson Pass. It only takes a minute or two to realize that they know what they are talking about and are the real deal. I met Nelson decades ago before all of his current fame, back at that time i knew he was someone special, when i met David Wilson in the 70's i got the same vibe the same vibe i got from Alberto this pass weekend.

I too own the AGD Audion's and concur that they are special regardless of class. Spend some time with them in your own system and you will understand.
atmasphere's avatar
atmasphere
11,807 posts
 
Spend some time with them in your own system and you will understand.
I think he already does :)
What parts are used specifically the GaNFET which is patented.
A class D self-oscillating amp will have some sort of converter to convert a square wave to a triangle wave. It will have a comparitor IC to compare the triangle wave to the incoming audio. There may be divider networks to deal with offsets in the comparitor, and the also offsets from the outputs of the input buffer (usually some opamps to give the circuit a little more gain and also increase the input impedance).  After the comparitor there may be level switching circuits to put the comparitor output at the right voltage level for the driver circuits. After the comparitor is also where any dead time circuitry will be located. There are a variety of driver devices available- these are used to drive the gates of the GaNFETs without exceeding their range or causing weird oscillations.


Almost all of these parts are available off-the-shelf. Its good that he has a related patent; this is certainly helpful for knowing how to use the devices :) From what I've seen of the specs Alberto clearly knows what he's doing.
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