Regarding power output of the in production GaN-based class D amps, I’ve been criticized for posting what is from the manufacturers’ own websites. So this is my last attempt to compare their respective outputs:
ADG Vivace: 200W into 4 ohms with 0.1% THD using a 1kHz signal
Technics SE-R1: 300WPC into 4 ohms with 0.5% THD using a 1kHz signal
Merrill 118: 800W into 4 ohms (no THD or frequency signal data specified).
Every manufacturer, has a different approach about how to provide (a bigger) number, when related to the output power.
It is the main number that attracts first attention, and for the most part actually it means not very much, but yet that is why the temptation (thanks to the lack of industry standards) to find a point in the THD vs Frequency chart as favorable as possible, and get it as big as possible.
We have chosen to provide a number, within the characteristics of the design of the GaNTube, that still has some more meaning, in relation to a power level that can be delivered within reasonable quality (low distortion) and generate a "ears-drum safe" sonic pressure, if ever used.
With a 100W input signal, a speaker with even low efficiency, let's say of 87db at 1W/m., can generate a pressure of almost 110db...so...
By the way, comparing the power specs, it seems to me that the only way to get to that power level, considering the GaN MOSFETs available in the market, both Technics and Merrill amps are likely adopting an internal bridge configuration, for the power stage.
In other words, with a bridge configuration, the power would have be 4x. (The load sees twice the voltage swing, and since P=V^2/R if V is double then P is 4x).
The Power stage integrated into the GaNTube is not in bridge mode, it is a single stage, and for whoever is curious, uses a custom integrated half-bridge GaN Mosfet made by IR (now Infineon).
Also, I would like to share something more. When the idea of the Vivace was conceived, so to speak, we choose to go with an unique design, both for the technical and the aesthetic one.
That decision was made because we wanted to convey the message that a ClassD amp can sound better than the best classic Tube amp, and actually look very nice too and different (not just like another metal box of exaggerated dimension).
The aim was in principle to liberate the Class D topology from the "stigma" it has been carry-over for way too long, and for sure now, at least with GaN, without any foundation or (de-) merit; actually all the contrary. And it seems it is finally happening.
In any case, what I found peculiar too, is that from all these comments, now so many, it seems only very few people actually have had the opportunity to do some true comparative listening tests.
By reading the comments, whoever has done it, more and more it sounds to me like someone that "...has seen the light" (sorry for paraphrasing St.Paul...but...)
So my suggestion is...type less and listen more...go get to listen to these amps!
AGD