Class D amplifiers. What's the future look like?

@atmasphere THANK YOU for that explanation. Now it finally makes sense.  We are not "doing" Class-D "just to be doing it" for the fun of new technology - there is logic behind the "why" of doing it - which is to achieve lower distortions in the audible range, to make music sound more like music.  That answers my question perfectly.  I visited your website. Beautiful amps. Good luck going forward. 

I would say the future of class D is Lyngdorf.

Reduced size, weight and cost are not benefits at all - they make the amps look less substantial. Kind of toys.

Reduced heat is a plus, though, especially from ecological point of view.

I’ve been wanting to try Class D amps for a very long time - for energy efficiency and heat management (I don’t have AC). I put it off for years because I was concerned about some of the criticisms. I was convinced after Ralph said his Class D was as good as his tube amps, and also after reading some of the AGD reviews and reading about Alberto’s history.

I just got the new AGD Duet monoblocks - I went with AGD because I wanted the extra power, 300 watts at 4 ohms, and because of the possibility of upgrades as the technology improves. I’m still breaking them in but they already sound great. My other SS amps are the Pass INT-25 and the Boulder 866. I’m in the process of putting together my "retirement" system and I’ve made a LOT of recent changes, so I don’t want to try to compare the AGD Duets to the Boulder 866 yet, but my initial impression is that, in my system, the AGD Duets are certainly as good as and possibly better in some aspects. I’m using the Playback Designs MPS-8 CDP/DAC with balanced interconnects connected to the Duets and using the PBD volume control, driving YG Hailey 2.2 speakers.

At some point I’ll put the Boulder 866 back in for a comparison, but my plan is to keep using the AGD Duets with the YG speakers and moved the Boulder to a second system. Alberto has been great to work with and I highly recommend checking out his web page that has info on his designs and his test results.

At some point I also want to try Ralph’s Class D amps, and it would be fun to compare them to the AGD. If anyone in the Denver/Boulder area has the Atma-sphere amps, I’d be willing to get together to compare them. I’m glad I waited this long, but I do think now is a great time to try the AGD and Atma-sphere Class D amps.

Bob Carver
"I built many of them right here in my own laboratory with the thought they could and would fulfill that final promise.... I was never able to build a Class D amplifier that sounded as good as a linear one."



Cyrill Hammer (Soulution Audio)
"If you want to have your product performing at the cutting edge it is not possible with today's known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz."



Lew Johnson (Conrad Johnson)
"I tend to think that Class D circuit design is an approach best relegated to producing low-cost, physically manageable multichannel amplifiers where one might accept some compromise in sound quality for the sake of squeezing five, six, or seven 100 watt channels into one moderate-sized package for a budget home-theater installation."



Vladimir Shushurin (Lamm Industries)
"No, it is not. And I would like to respond to the second part of this question with an allegory. Any field of human activity defines a number of requirements which, when properly implemented, guarantee a positive outcome. For example, the basic requirement in the army and sports is an able-bodied individual. So, it would be quite natural to concentrate on searching for such an individual (especially as we know where to find him). However, out of the blue we decide to choose a feeble-bodied person who, on top of that, is encumbered by various diseases. Having made this decision (which is a priori improper) we start justifying it to ourselves and others by citing the great state of our medicine, which is capable of curing many ailments."


Fumio Ohashi (BAlabo)
"No. Class D can't really be considered for super-high-end performance in its present stage of development, although it can be fine for mid-market products."



Nelson Pass (Pass Labs)
"Does a $10 bottle of wine compete with a $100 bottle? Of course it does, and it often wins based on price. Right at the moment Class D designers seem to be still focusing on the objectively measured performance of their amplifiers. I expect that at some point the economics of the marketplace will encourage them to pay more attention to the subjective qualities, and then they will probably play a greater role in the high end."



Jürgen Reis (MBL)
"I have worked a lot lately with Class D. Ninety-nine percent of Class D circuits are not competitive with linear circuits. Most Class D sounds sterile. It's tricky to figure out what to do to compensate for that."



Thorsten Loesch (iFi - AMR)
"I have yet to hear a pure class D Amp I’d rate above "below average for solid state" (which is not very high performance). In a little update of my classic 'Valve Analogue Stages for DACs' I wrote: "Perhaps more crucially, so called Class D Amplifiers, which have in recent times sprouted up like mushrooms after a warm rain, continue to use the straight two or three level modulation scheme described above. And thus they still require the use of heavy handed noise shaping to attain anything like acceptable 16 Bit Audio performance.The clock frequencies for these amplifiers are usually at 300 KHz to 1MHz in the best cases. That is 3,000 to 10,000 times lower than what is required to attain 16 Bit / 44.1 KHz performance without noise shaping and other forms of signal manipulation! And again, one is baffled and perplexed by the rave reviews many Class D amplifiers receive, as baffled as one was about the late 90s reviews of timeslicing DACs. The best of breed I have auditioned were certainly not bad; however in direct comparison to the best available valve and solid state amplifiers they do not produce a very good sound. Well, at least they offer novelty and the reviewers something to write about other than another (however good sounding) 8 Watt valve amp. Incidentally, the best sounding Class D amps tend to be really low power single chip devices (putting out little more than the 8 watt valve amps), presumably because they are faster AND because they always work near what one might call a full scale, if they would be DACs. On second thought, they of COURSE are DA Converters and where a Class D amplifier accepts analogue input directly it is an A2D converter followed by a power D2A converter! What an insight!?"



Mark Levinson
"Interleaving of multiple Class D Amplifiers is potentially a step in the right direction, but does not go far enough.Personally I think that the best option would be something that combines a Class D Amplifier for the heavy lifting with something Class A for fine detail. Probably implemented in the style I did for AMR’s AM-77 "Jikoda" Style. In this case both of the circuits involved can operate fully open loop. In many ways the problems in Class D Amplifiers are analogous (but not identical to) those in Class B Amplifiers (but without an option to implement Class AB or Class A) so similar solutions apply. All Class D amplifiers are essentially delta-sigma DAC’s. If the input is not digital PWM signals (aka "DSD") but analogue audio then it is also a Delta Sigma Analogue to digital converter...Now DSD (aka SACD) which to my ears fails to come close, never mind equal true PCM CD Replay in most aspects of sound quality, operates at 2.8MHz switching, or around 10 times as fast as common Class D Amplifiers...Why anyone would want to listen through an A2D followed by an D2A Converter that are around 10 times worse than single speed DSD is beyond me. But with enough hype and snazzy naming it cannot help but sell high and wide."