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GaN-based Class D power amps

The use of GaN-based power transistor tech is now emerging for Class D audio power amplifiers. Seems appropriate to devote a forum thread to this topic. At least 3 companies have commercial class D amps in their books:

Merrill Audio, with their model Element 118 ($36k per monoblock, 400 W into 8 ohms, 800W into 4 ohms), Element 116 ($22k per monoblock, 300 W into 8 ohms, 600W into 4 ohms) and Element 114 (coming soon). 
https://merrillaudio.net

Review of Element 118 at this link:
http://www.enjoythemusic.com/superioraudio/equipment/1018/Merrill_Audio_Element_118_Monoblock_Amplif...

ADG Productions, with their Vivace Class D amp ($15k per monoblock pair, 100W into 4 ohms). (The designer emailed me indicating he has another product in the pipeline.)
http://agdproduction.com
Review of the Vivace Class D moniblocks at this link (warning: link might not work (1/11/2019)):
https://positive-feedback.com/reviews/hardware-reviews/agd-production-vivace-gantube-monoblock-ampli...

Technics SE-R1 Class D stereo amp ($17k per stereo amp, 150WPC into 8 ohms, 300WPC into 4 ohms) 
https://www.technics.com/us/products/r1/se-r1.html
Preliminary review of the Technics SE-R1 at this link:
https://www.stereophile.com/content/technics-se-r1-digital-amplifier
Technics also has a lower priced GaN-based class D integrated amp in their catalog:
https://www.technics.com/us/products/grand-class/stereo-integrated-amplifier-su-g700.html

Anyone listened to or own any of these amps?


celander
celander's avatar
celander OP
1,036 posts
 
I thought it was a taboo to use negative feedback in a class D design. But then again, I am not so certain that this Lyngdorf amp is a class D amp in the first place. See this post in the link below from one of the principal designers: https://www.diyaudio.com/forums/class-d/333672-breakthrough-dd-amplifier-3.html
erik_squires
5,268 posts
 
I thought it was a taboo to use negative feedback in a class D design.

Nope, it’s inherent in a lot of Class D. It doesn’t work quite the same way though. Some uses local feedback, which does not include the output, and some do.

Feedback and a triangle wave oscillator is how the analog input is converted to PWM output.
celander's avatar
celander OP
1,036 posts
 
Erik, I agree negative feedback is used in a lot of class D designs. But I guess this particular amp is not a class D amp. Not saying it isn't a great AB amp (or whatever it is), just does not seem to fit into this thread's focus.
atmasphere's avatar
atmasphere
7,068 posts
 
Nope, it’s inherent in a lot of Class D. It doesn’t work quite the same way though. Some uses local feedback, which does not include the output, and some do.

Feedback and a triangle wave oscillator is how the analog input is converted to PWM output.

Class D does not have to use feedback.

PWM (pulse width modulation) does not use any feedback at all.

In a switching amplifier you have something called 'propagation delay'. This is a time delay caused by the fact that it takes a while for a device to switch on or off. Put a number of devices one after the other and there can be a quite measurable delay from input to output.

For this reason NFB taken from the output and applied to the input will always be slightly out of sync with the signal its supposed to correct. For this reason it will add distortion of its own. Fortunately class D amps don't have to use feedback to have low distortion.



celander's avatar
celander OP
1,036 posts
 
+1, Ralph, for educating and keeping us on track!
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