Competitive class D amp suggestions

@rsf507 thanks for the link. I have a bit better idea about Atmasphere amps than before. I may also ask by email. As to the distortion, I don't know what THD really means. As noted in this thread, my class A tube SET amp with THD 0.5 gives notably cleaner sound reproduction than my class D amp with THD of 0.001. 

https://www.ap.com/blog/thd-and-thdn-similar-but-not-the-same/

It seems it is about time to clarify a few things for the benefit of all my fellow audiophiles and customers.

The GanTubes are not “fake tubes”, they simply are not Thermionic Tubes, the same as a LED Lamp is not a “fake bulb”, it is simply not a filament-based bulb.

In some of the comments, there is a statement that says: that “GaNTube” is just “marketing.

Well, I beg to differ, it is much more than marketing!

There is a lot of engineering and a lot of interesting solutions to deliver a great sound, and much more added value to all the Audiophiles (btw…have you ever tried to put a model of a boat inside a bottle? Do you think it is so easy? 😊)

Let me ask a simple question:  where can you find another example of a Hi-End Audio amplifier that can be upgraded in less than 10sec without the use of a screwdriver or any other tool for that matter, and without any risk of electrocuting the user? (Yes…rule #1 in marketing is never ever killing the customer 😉).

A “fake tube” with an octal socket?! Well, the octal socket we use is a standard socket that has been continuously used since the 1930s… the standard socket of any bulb, (LED or Filament based) is around for even longer. They both are the same as they were when they hit the market…100years ago. 

I think we can agree that if they had not been reliable as an electromechanical part, they would not be around anymore…after 100 years.

GaN technology and related product roadmaps are still at a very early stage compared to one of the silicon-based components (70years of development). So to us, the possibility to offer an easy and simple way to “upgrade the sound” by swapping a new “Tube” containing a more advanced version of the GaN Mosfet (or a more advanced design of the power stage), while preserving the value of the object (the amplifier) in time, is not a trivial thing.

With the GaNTube platform, we offer that value; in fact, we already introduced in early 2021 the MKII GanTube version for the Audion and the Vivace. Thanks to the upgrade now they are switching at 800kHz and can deliver 200W and 250W (up from 170W and 200W/4ohm respectively).

The AGD Tempo is designed with the same principle of upgradability, but with far less simplicity in the operation. The AGD Tempo idea was conceived with the idea to deliver a lower entry point price to the technology, in a very compact housing and retain as much as possible all the sound characteristics of its bigger siblings.

The AGD Tempo is not technically a Dual Mono, the 2 channels share a common main power supply (larger but single).

I am sure you know that regardless of the definition of dual mono, and design of a 2-channel amplifier housed in a single chassis will always have some level of influence in the sound stage, that is due to the magnetic induction generated by the flow of high current in one channel picked up by the other channel, and vice versa.

However, from the layout point of view, the AGD Tempo has been designed in a way to minimize this effect, with reduced stray inductances and opposite direction routings (where feasible), but physics is physics…

The Audion and the Tempo are very similar in all aspects of the sound stage, depth width, and the holographic effects that all AGD GaNTube and GaNPower Class-D amps (well better to call them Class-AGD 😉) are getting famous for, and of course for their technical specs. They both share the same identical components and circuitry.

If you have the opportunity, please read the review from Rick Becker on “Enjoy the Music”, he landed to the same conclusion. https://enjoythemusic.com/magazine/equipment/1221/AGD_Tempo_di_GaN_Stereo_Amplifier_Review.htm

Of course, it is impossible for me to choose which is the better between my 2 babies, I am a true proud parent!

So again, thank you for the opportunity to clarify some of the points brought forward in this thread, and call me/write for any further questions or any help.

Atmasphere class d amps can also be interesting. I did not find them on the site and have no idea on preferences made in their design. Neither i know if there are already completed models. Can Ralph provide  more detail? 

I can. Its been the most successful product entry we've ever had. We started shipping last June. We didn't put up the product page until about 2 months ago. Early on the project (about 5 years ago) we had a prototype that demonstrated that the idea was worth pursuit- and that a class D amp need not have any audibly objectionable characteristics.

The simple fact is most output sections in traditional amps have distortion product based directly on their linearity. And since the output devices are not all that linear, feedback has to be applied to make them look better on paper. That's been a problem in solid state amplifier design since the inception of solid state. Class D does not deal with that problem, since the output section does not rely on linearity at all- it switches. So the distortion generated has entirely different sources!

One problem in traditional designs is getting enough gain and bandwidth to support the amount of feedback used. Traditionally this has meant that the feedback at 100Hz is quite a bit different from what it might be at 3KHz or 7KHz and as a result brightness and harshness has been present (put another way, if there isn't sufficient gain and bandwidth in the circuit, the feedback will decrease with increased frequency).

We've all heard this over the last 60 years of solid state amps; brightness and harshness is for many one of the worst failings of any audio system!

Class D offers a way around that, by allowing for profound amounts of feedback that is very difficult to do even with modern devices in AB circuits! With such high amounts of feedback its possible to build an amp that is both low in distortion while relaxed and detailed better than the best tube amps. To some this last statement might seem a bit weird but the experience of amps with low distortion not sounding all that good is common. At this point (and take this from someone who has been at this over 50 years) I'm very convinced that tube power amps are on borrowed time.

I play a set of our class D amps at home if that tells you anything.

PS Audio is now having a sale on all their class D amps.    Pickup a couple M700 mono blocks for little over $2K.