Expanding the Class D Conversation: How Would You Characterize Their Differences?

I have had a LOT of class D and other high efficiency amps and have found that if you chose carefully, you can go back to the mid 90s and find good sounding gear.  

I am currently running what is probably the ultimate Class D, the Linn Klimax 800 but have owned or spent time (taken on trade) older Linn Chakra amps, Rogue, NAD, Primare, AVM, Atmasphere, AGD, Classe, Jeff Rowland, Lyngdorf, Peachtree, Sunfire and I am sure there are others I am not thinking of.  I have also heard Merrill amps in a stunningly good system and would call out a unique class A design that runs relatively cool from Westminster.  

My experience with Hypex/NCore has been positive but in two of the three cases there was a tube stage in front of the module (Rogue & AVM 5.2 Integrated).  These have a reputation for being a hair edgy but a solid tube stage in front takes the edge off and adds 2nd order harmonics that make these phenomenal amps.  The AVM 5.2 level integrated was what I used for a long time as my reference and before I started Verdant, the Rogue Hydra was the power amp I chose. Primare does not use a tube stage and these amps are still awesome and sound as good as any purification designs I have heard.  

Pascal modules are used in AVMs all-in-ones and some of the most expensive Class D amps made in Denmark.  The modules are expensive and sound really good and you could easily mistake this for a well manufactured bi-polar AB design.  

AGD was a staple for me for a long time and these amps sounded so good I found the closest comparison was to my tube monos, particularly the Grand Vivace's.  I am no longer an AGD dealer but that was driven by the fact that I did not make enough margin when taking trades. These sound like a Class A amp or AB that is biased heavily toward Class A.

NAD and Lyngdorf use Purifi.  I have said in another thread that the C298 is not the best amp I have ever heard, but it is the best $2K amp I had ever hear.  This was a few years ago.  I stand by that.  Brilliant product.  Clean and clear without edginess.  I would put this up against any bipolar amp under $10K and it will hold its own.  Lyngdorf is a different animal and the experience with them is about room correction.  Tougher to judge the amp.

The reality is Bob Carver's Tracking Down Converter back in 1995 or 96 was the first amp in this class that sounded genuinely good.  Bob knew what he had and patented it but unfortunately Sunfire never had the commercial success of Carver Corp and this stuff flew under the radar for a long time and it definitely skewed toward home cinema rather than two channel audio.   These amps were amazing sounding and delivered mind boggling current. Then Sunfire was sold and the product line just died.  

Linn's designs are proprietary and they do not use off the shelf modules so nothing sounds quite like them.  These are monster's in terms of current and power and deliver detail and clarity without edginess or fatigue.  These amps regularly deliver surprise moments where I hear a detail I have never heard in a song before.  It happens all the time and to songs I have listened to a lot.  They sound like an elite Class AB but you get 400w into 8 ohms doubling down to 2 ohm monos that are ~65lbs as opposed to 120 to 200lbs.  I have had these up against some big manufacturers and it is clearly taste driven at this level but they hold up.

Regarding Merrill, I have never had a trade in of these but do have a friend who has a set of their monos driving a pair of Magico M3s and his system is absolutely wonderful.  Sincerely a system that you can listen too all day with no fatigue.  Detail, power and clarity with no edge or harshness.  

Finally, I would mention Westminster.  WestminsterLab is Class A because its output devices conduct continuously through the full waveform (no crossover switching like AB or D), but it achieves efficiency by using a highly regulated, tightly controlled power supply and optimized bias that minimizes wasted current outside the linear operating window. In other words, the signal path remains pure Class A, while the power architecture is engineered to reduce heat and excess dissipation without altering the conduction behavior of the output stage.  Basically a Class A amp that behaves a lot like a Class D.  These things are awesome and I had a pair in for a few months and have heard them on some incredible systems.  

There are a lot of amazing Class D options, even at the cost no object level and they deliver.  I don't know why, with the level of elite performance we are getting from Class Ds these days, this is even a discussion anymore.  

Full disclosure, I am an NAD, Linn, Primare and AVM dealer.  I used to be an AGD dealer but the margin economics did not work with taking trades.  I am not a Westminster dealer but have a strong relationship with Hear This and am a dealer of other products from Gary.  I have no affiliation with any other brand mentioned.  

General update: I'm getting my hands on an AGD to try against the NAD M23. I will report. That will mean I've had three types of amps to try out in a short time – Hypex-based, Purifi-Eigentakt-based, GaNfet-based. I'm pleased about this.

I tried the NAD M23 with my 6SN7 tube amp last night. Zero fatigue. Other good Class D attributes were there.

@sdl4  Thanks. I'm not sure how critical the LPS is; I've heard there are now very good switching power supplies. I bet it has more to do with Ralph's ears and brain – to put it simply. I have a dealer near me (about an hour away) and if I can, I'll try his amps. 

I've also heard on a video that AGD's ganfets are from a supply that are specially audio-apt. Not sure what the others' are, but in all cases the engineer has to adapt his/her materials to the application. 

@verdantaudio 
Thanks for your long and descriptive post. Appreciate you relating your extensive experience.
I didn't find that a tube in front of a very well implemented Hypex/NCore took the edge off.

I'm curious about the Pascal modules, and obviously about AGD. The NAD M23 sounds pretty good but I appreciate your comment about the C298. That is sounding like a real bargain, especially used. Wonder if it could be modded/upgraded somehow to take it to the next level. I know a tech...

Sunfire story is super interesting! Really have not read much about Linn. You have me curious. Thanks for that!

The Merrill and Wesminster anecdotes are also very helpful. 

@ashoka  Your statement "class D was preferred because of Efficiency and cost." If that was all there was to it, you're right – there would not be a debate. But there is a debate, so...

@parkergetdean 
Super helpful to know about the SMSL PA200s. Jay Iyagi praised the heck out of them on a recent YouTube but then...

@greenngoldcheesehead 
It's good to keep in mind how good some of the class A/B amps are at doing what people laud about Class D. There's this notion that "Class D" are the future and then I think, "Wait – aren't there really good Class A/B amps out there? Yes, there are." But maybe they can't quite do what people like with Class D? Not sure, really.

@yyzsantabarbara 

Thanks for the GREAT description. Fascinating how a DAC can really impact even the strong sound character of the amp that follows, even creating, with the Class D 6.5 amp "a juicy Class A like sound." Of course, some people are not looking for a Class D amp with a Class A sound. They want something good but different than Class A. 

Good to know the 6.5 does not have glare; interesting that it was "lifeless" in the wrong combination. In other ways, it seems to really shine; makes me wonder about some of the SMSL amps. They sound like budget-helpful options, possibly. (Not necessarily for you, just generally.)

@hilde45 I will say the limit to my tube/hypex experience is Rogue and AVM 5.2.  Those I think are good.  Primare has no tube and I don’t fine them edgy at all. 

NAD is an amazing value.  I think you will struggle to beat it at those price points. 

AGD sounds a bit more liquid than NAD.  NAD sounds like a good bipolar to me while AGD sounds more like a MOSFET or maybe a MOSFET/bipolar hybrid.  They are awesome.  

Regarding Linn, the older Chakra amps at the Klimax level are really, really good in the sub $20K price tier.  I have never heard their Akurate level amps which are not crazy expensive.  I should probably borrow one for demo. 

The new amps using the new PSU tech are not for the faint of heart in terms of price.  The 800s are a hair over $100K/ pair and the 500s are in the $65K range.  That said, they legit go toe-to-toe with NAGRA, Burmester, D’ag, etc... and hold their own.  

@verdantaudio Thanks for the continued, helpful description. The audio community is really fortunate to have you as a dealer and willing to participate in conversations. 

I decided to do a little research on Linn, and came across this really interesting review in Stereophile. The discussion here about linear vs. switching power supplies really helps bust myths/opinions about switching power supplies if they are done right. Linn is quite a company, it seems, and offers an interesting forward path.

@parkergetdean you should really try a quality class D. Oh and run them in. 

Also curious as the the components that comprised the system used to audition. 

I had two SMSL PA200s in dual mono mode a month ago. They were very harsh,  with limited sound-stage, I returned them.