My new review for The Absolute Sound comparing AGD GAN amps with BHK300’s

So much WRONG here!

Comparing a Class D to an analog discrete amp, for one! Class D has far fewer parts and switching style supply.

And that load of crap about “unobtainium” audio GaN MOSFETS!!!  Gees Louis!!! Switching MOSFETS have been used in high dollar audio amps for DECADES!! GaN MOSFETS are still MOSFETS!! Most are very linear but the GaN have efficient on/off states. GaN have efficiencies for switching use at ULTRA-AUDIO FREQUENCIES, hence THE CLASS D amplifier!!! DUH!!!  
 

So this is supposedly an “AUDIO GaN MOSFET”…….. used as a switching device in a CLASS D audio amp!!! You HAVE GOT to be kidding me!!!! The GaN devices aren’t even used in AUDIO FREQUENCIES!! In a Class D amp, they are used as very high frequency switching devices, and NEVER SEE any frequencies between 20-20kHz!!!  
 

And then, the CUTE little mounting of the switching circuit inside a glass envelope!!! Oh for Pete’s sake!!! REALLY????!!

Sorry!!! But this review is loaded with disinformation and downright misleading claims by the manufacturer, glossed over and passed on to gullible consumers!!

REALLY????!!

Its perfectly valid to compare amps of different classes of operation.

Regarding the 'unobtanium' GaNFET, I understand your skepticism- I reacted the same way. The designer claims he uses a device 'designed for audio'. As you know, GaNFET's main advantage, their raison d'etre, is for switching so of course any GaNFET could be used but if you wanted to optimize one for a class D audio amplifier it would have a low output capacitance. That was something we considered when we chose the parts we use as well. So we can assume that is what is being used. That is the extent of being 'designed for audio'.
 

This is hilarious, actually!!

If I use a switching semiconductor to switch at 2 mHz, are you going to call that device an “audio output” device???

Thats what these GaN devices are, and that’s how they’re used here! That’s how Class D amps work!  These devices are no more “audio devices” than the devices used to control industrial induction motors, or used to control motors in EVs!! Fact is, both GaN and SiC were developed for exactly these reasons: Efficient control of induction and DC motors!!!

This is a total scam to say these devices are “audio” rated, or even operate at audio frequencies!

Peoples’ lack of understanding of Class D amps makes for easy victims of false advertising!!

 

soix

8,602 posts

04-17-2024 at 01:34am 

@wolfie62 Not really sure what you’re saying.  GaN FETs are clearly different from MOSFETs, and the performance advantages of the former have allowed amp designers to not only more seriously rival traditional amps but are now starting to surpass them.  When a company like Atmasphere makes a GaN amp that the designer in most ways prefers to his MUCH pricier OTL tube amps that’s pretty strong evidence that something significant has changed.  Again, not really sure what your point is here.
 

See my post above. That’s my point! 

@atmasphere

To my knowledge only one company anywhere has made the claim that the devices they use are ’audio rated’ as you put it (although I am not sure they used those words, so paraphrasing). The only parameter that might make that so is the low output capacitance I mentioned. Beyond that, yes, the output transistors of any class D amps are designed for switching with power.

A loudspeaker is a motor. Also a transducer.

Output capacitance is really not a “thing” for class D amps, other than internal capacitance (parasitic) can effect the maximum switching frequency and possibly efficiency of the switching device, how much of the switched energy is converted to heat. That’s the only advantage of GaN devices; higher voltage, less heat, higher switching frequencies. It has nothing to do with transfer of energy to transducers (loudspeakers).

Im not a “naysayer”. I’m just a “factsayer”. I strongly dislike those manufacturers or reviewers who use consumers’ ignorance of technology to sell stuff.  These “proprietary” GaN “audio grade”devices grabbed and used for their singular audio use/purity is a “snake oil” claim. Pure and simple.

@atmasphere 

Output capacitance of a class D isn't a thing as you say, but output capacitance of the output devices is. Its nice to have that low for better switching.
 

Exactly what I already said. And “low output capacitance for better switching” is exactly my point!! Those output devices never see audio frequencies!! They are switching at much higher frequencies than the audio spectrum!!

So finally we are in agreement. The GaN devices are switchers and are NOT audio devices.