Which Class D Amplifier? PS Audio, Ghent, Nord, Merrill or other???

kgturner,

     I don't know what the general opinion of those following this thread is but my opinion is that these mono blocks are excellent amps.
     Kharma, mainly a hi-end speaker and cable seller at the time, introduced their first  class D amps  (the MP150 and MP350) in 2007. Kharma owner, Bruce Oosterum, collaborated with class D UcD inventor, Bruno Putzeys,  on these UcD based amps.
     Putzeys had claimed to be able to bend the sound of any class of amp, be it A, AB or D, to his will.  So the design goals for the new Kharma amps was to make them sound like a tube amp in mid and high frequencies and retain class D's traditional excellent bass response. 
     As you stated, according to the reviews of the MP150 from The Absolute Sound, Stereophile and 6 Moons at the time, they were very successful.
     Around 2010, I heard a pair of MP150 mono blocks driving a set of Magnepan 20.1s playing vinyl and it sounded spectacular.  I wanted to buy a pair for my Magnepan 2.7qrs but the price was too steep for me at that time; about $7K/pr. if I remember correctly.
     I'm very satisfied with the much newer and higher powered D-Sonic class D mono blocks I'm now using with my Magnepans but I wouldn't be surprised if a pair of the Kharma MP150 monos, even a 10 yr old used pair, sounded just as good or possibly better.  However, I heard them on the top Magnepan speakers which isn't really apples to apples, either. 
     I'm also not sure whether Kharma has updated the MP150 over the years.  I think Kharma has since offered an MP1000 model amp that is class A/AB.

Tim

I found some interesting You Tube videos of the new ADG Vivace GaN mono blocks:

1. A pair of the new ADG Vivace GaN monos driving the mids/treble of a biamped speaker with the bass driven by an older pair of Rowland Model 12 class D monos compared to 2 pairs of Rowland Model 12s driving both.

2. A pair of the new ADG Vivace GaN monos driving the mids/treble of a custom biamped Magnepan speaker without the bass being driven at all compared to 2 pairs of Rowland Model 12s driving both the mids/treble and bass.

Here are the links: https://www.youtube.com/watch?v=KJb3pOY4tGA
https://www.youtube.com/watch?v=KJb3pOY4tGA&t=392s

3. B&O ICE Module 250ASX2 with tube input. (500wpc@8) vs. Jeff Rowland 535 (250wpc@8) vs. AGDProductions Vivace monos.

Here’s the link: https://www.youtube.com/watch?v=b-HFVPvWHTw

It is true that the comparison is limited by the audio quality on a You Tube video, but I found the audio quality sufficient enough to still convey the clear superiority of the GaN amps. Of course, I’d prefer comparing the sound quality in person.
I also thought the ADG Vivace amps, with the gimmicky large tube shell containing the GaN FETs protruding from the top of the amps, actually looks much less goofy in action than I originally thought it would. My current opinion is that it’s a good tip of the hat to the fondness most tube lovers, including myself, have for the warm glow of tubes in a darkened room that is remininscent of good music flavored with a touch of euphonic joy.
These videos struck me as satisfying confirmations of the benefits GaN FET technology can contribute to the sound quality of virtually all solid state amps.

Tim

Correction:  I mistakenly stated the older Rowland Model 12 amp is class D in my last post.  It is actually a class AB amp.

Sorry,
 Tim

   I'm also curious about how your development of a class D amp is progressing and whether it will utilize GaN or any other newer technology.  

@noble100
Right now we're not using GaN transistors but they are certainly on the radar. So far we've been building our modules by hand. GaN devices are much smaller than what we are using, which makes the assembly a lot more difficult (or easier, if we farm it out). Otherwise progress seems to be pretty good.

Hello atmasphere,

Thanks for the update. Very interesting and surprising, too. I’m not surprised you’re building your class D modules by hand but I thought you’d decide to utilize the faster switching GaN FETs in your amp. I would think not using them would handicap your amp’s performance in relation to the competition. I assumed you’d choose the best parts for each amp function in order to optimize overall performance.
I’m just an enthusiast of good music played through high quality audio equipment but even I can hear the improvement in sound quality of the ADG Vivace mono blocks despite listening to them on a YouTube video on a laptop via headphones. I think the improvement would likely be even more obvious and impressive heard in person.
I may be attributing too much credit to the faster GaN FETS, rather than the typical silicon MOSFETs , for the improvement in sound quality I hear in the new ADG amp. I know there're many other design factors involved in determining an amp’s ultimate sound quality.
But I understand that you’re an amp designer who’s also responsible for running a successful company and there’re very important factors involved in your choices that I’m not aware of. You certainly don’t owe me an explanation, I think I’m just a bit perplexed and disappointed.

Best wishes,
Tim