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

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."

@deep_333 I've seen that list of quotes before. They got debunked due to their age. 

A lot of those quotes you listed are from nearly 20 years ago. At that time I was of the same opinion as seen in them. One way you can date the quotes: look at Thorsten Loesch's comment about a 300KHz switching speed. No-one has made class D amps with that low a switching speed in a very long time 😁

So these comments can be discounted as simply out of date.

Your comment about GaNFETs seems a bit uninformed to me. Its not that GaNFETs are somehow 'the answer' so much as when they started turning up was also about the time that class D got a lot better figured out (and that was ten years ago...).

There's long been a tubes vs solid state debate on the internet, older that the internet itself. All technologies improve in time so one can safely conclude that sooner or later solid state would get good enough that tubes would simply be eclipsed. To tube aficionados like myself this also means that that new technology will eclipse solid state A and AB amplifiers as well.

I cannot speak for other manufacturers, only myself and that should be taken with a grain of salt since I am associated with a manufacturer. I've made no secret that I replaced my triode class A OTL amplifiers with a set of class D amps about two years ago and I don't hear any tradeoffs whatsoever. The class D amps are every bit as good and better in some ways then the OTLs. FWIW, the OTLs have been getting rave reviews and awards in the high end press since sometime in the 1990s.

As a result I'm of the opinion that class D is something to be reckoned with and isn't at all as you described; it dominates what we in the high end audio world call 'mid fi'- stuff you get at Best Buy and the like. Its been making inroads into high end the last 20 years and at this point, seems evolved enough that any manufacturer of amplifiers will be going out on a limb if they don't get class D figured out. Its that simple.

@atmasphere , It really comes down to one's 'point of reference', i.e. what type of gear a dude's spoilt by or not, what type of gear he grew up with (what type of gear created his taste pallet to begin with, etc...).

I grew up listening to my old man's class A vintage Pioneers and so on...That type of sound sticks with you, y'know? I spent years with most of Nelson Pass's stuff, cycled through some of Gryphon's stuff, etc, etc and this is my current list (spread out among different rigs)...

Luxman C900u+M900u, Yamaha C5000+M5000, Technics SU-R1000, Schiit Tyr, Zhongshen Class A, i.e. this is my point of reference at the moment. I am done buying sht for now.

But, for years, or atleast since 2000, i've been probing Class D every few years. The primary goal there was to not have space heater amps running in the room ---> Frequent HVAC activity ---> increased HVAC induced noise floor ---> loss of fidelity. I tried, but, every freaking time, i was let down by them. The Technics was the most i was able to deviate from Class A/AB, but, even that amp feels like a letdown some days. 

I wish my ears were more forgiving. I think I could make some Class D work for my ears with tube line stages and dacs, but, i really don't want to deal with the confoundedness/pestilence/mainteance crap with tubes anymore...

Some pieces can spoil a dude and maybe it makes one's likes/dislikes appear a bit stronger (more pronounced in articulation perhaps). When i am a guy on the internet, i am joking about stuff. It makes me live rent free in @soix 's head somedays, for instance 😁. But, i've walked into houses of dudes in my area with all kinds of gear at all kinds of price points and i don't say anything to hurt their feelings. I have a few drinks and i'm rocking with any kind of gear, i.e., I am a doll in real life. 😁

I am sure your stuff would be great for a lot of guys.

@deep_333 ,

Thats some impressive gear you have there. Would definitely like to see your setup

Create "Virtual System" has not worked in months (Error = User can’t be blank).

Gear List:

****2 channel, Room 1****
Speaker#1: TAD-E1TX
Speaker#2: Von Schweikert VR-55
Speaker#3: GR Research NX Studio Kit/DIY
Subwoofer: GR Research openbaffle servo kit DIY, Q = 2
Amp 1 : Luxman C900u+M900u
Amp 2: Yamaha C5000+M5000
Amp 3: Technics SU-R1000
Processor: Theoretica Applied Physics - BACCH
DAC/DDC: Denafrips Venus/Hermes
Source 1: TAD-D1000TX (sacd player+dac)
Source 2: Technics SL-G700 (sacd+dac+streamer)
Source 3: Custom audio optimized PC with custom software
Treatments: Acoustic Fields ACDA, Acoustic Fields QD-23, DIY
Power Conditioning: Keces IQRP-3600, Audioquest Niagara
All cables: Audioquest

****Multichannel, Room 2****
Multichannel 5.4.4: Andrew Jones Adante
Fronts: Elac Adante AF 61
Surrounds: Elac Adante AS-61
Center: Elac Adante AC61
Heights: Elac Unifi Reference UBR62
Subwoofer: Rythmik F12G w/ GR research driver, Q = 4
Preamp Processor: Yamaha CX-A5200
Amp 1: Yamaha MX-A5200 for Surrounds, Height channels
Amp 2: Schiit Tyr (Q = 3) for front stage
Amp 3 (Stereo hybrid use, Q = 2): Zhongshen JA99 Class A
Treatments: Acoustic Fields ACDA, Acoustic Fields QD-23, DIY
Power Conditioning: Keces IQRP-3600, Audioquest Niagara
All cables: Audioquest

So you can see we didn’t go into this blindly. We knew the class D R&D would be a bust if it didn’t sound every bit as good or better than our OTLs (which, in the tube world, rule the roost when it comes to transparency and bandwidth...).

@atmasphere , From what i’ve experienced thus far, the type of stuff you do could work for guys who mostly roll with midfi (they may think it’s hifi) or don’t have a high enough "point of reference". But, that shouldn’t worry you. You could still make enough money selling to those guys. IMO, what you won’t be able to do is convince guys who roll with any higher level of gear that your stuff should be sufficient for them as well.

For what its worth, I do have a "digital" amp (noted above), the Technics SU-R1000. It would sound pristine for a lot of guys for sure. It works for me in some cases. I am contemplating pairing it with a tube pre or something else for it to be agreeable to me in more cases/more types of music. One could open its chassis and immediately note that it is a innovative engineering masterpiece. You could get it yourself, compare your stuff side by side and let me know where you think you stand....Or let me know when you can beat the Technics and i’ll take a look at your amp.

On the same note, Schiit did something unique and innovative with the Tyr...You could try it as well (it is a very affordable amp) and see how your stuff measures up next to it.

15k to 25k for 2 cheap Chinese boards in a box, aka class lousy D, so D maker can laugh his way to the bank? (Laughing at the big ol’ dumdums who paid him, bwaaaahahaha) No thanks...

Lousy D beat any class A under 100k? The Class D maker/naked emperor’s pride must be on a serious rise these days. Either that or the D lovin ASR psycho train chasing 0.00000000001% THD must be making more stops at the Audiogon station too these days.

In my third system I own the following gear, which I know most people would be jealous about:

Gryphon APEX Monos

CH  Precision L1 dual Line Stage

dCS Vivaldi APEX DAC stack

Wilson Audio WAMM Master Chronosonic

All cabling is Nordost Odin 2

This system sounds so alive that I have stopped attending to concerts. But you are correct - Class D sounds so lousy. Forget about it.

@milpai , nice stuff you've got....i've cycled through all kinds of gear, but, my true breakthrough in high end audio happened after discovering the ACDA treatment options from Aoustic Fields. I literally tossed all my prior treatments in the trash after I found this stuff. It is not cheap, but, at your level of gear, I would seriously recommend these guys for room treatment. Don't waste any cash on all the other crap out there w.r.t room treatments. A guy will truly understand the criticality of competent treatment when he experiences it (you will hear things impossible with any level of gear on its own).

What? A tube manufacturer and dealer comes on to a thread about "What’s the FUTURE of class D".....and puts down ALL class d amps without even mentioning what he has heard and specific A/B tests. Then he tells us all the cool stuff he has and then invites us to come and listen. He might as well pay for an ad on the side of the thread. His post has NOTHING to do with the thread and adds nothing to what it is being talked about. Just an ad. I have nothing against advertising......but to come on here with clearly an intent to sell and add nothing? Where is the LOVE? Do you really care about the future of class D? Obviously not. Do you care about people who like class D.....obviously not. Do you care about making money? Obviously.

 

1 page before that, another tube manufacturer who rose to fame selling decent tube gear for the past few decades has gotten into class D recently/apparently. Now, he wants to peddle it, make waves with it and thinks everyone would drop the sweet things they’ve got and get on his Class D bandwagon.

Most threads on this forum are steered by dudes with financial interests, typically a) manufacturers b) dealers incognito and c) their incognito/paid pied pipers, i.e. the ones who pretend to be genuine flipping customers jawdropped/blissed out by some product apparently. Everyone is required to know his bliss now apparently!! and he shall not rest until then!!! (whoop di doo). It isn’t about music or genuine end-users helping others.

If these guys are so desperate to grow their market share, beat down their competitors, boost profits, etc they should quit yapping with the same old sticks in the mud around here (who’ve been around the block and rarely change their conclusions about anything). If they were smart, they would go peddle on reddit or other AV forums. Go and grab some younger guys into general AV, computing, gaming, etc sitting around with significant chunks of cash. These are the type of guys who love music, but, sit around with awful sounding lifestyle audio gear (Bose, Sonos, soundbars, whatever). They simply don’t know any better. There is a big market share out there....and these guys could send their pied pipers to those forums for a bit so it isn’t the same ol’ crap over and over all day long around here. It doesn’t take more than half a wit to see all through this crap.

Checkout the review on @atmasphere Class D amps,

https://hifiplus.com/articles/atma-sphere-music-systems-class-d-amplifier/?goal=0_ff6dfd0295-606fd7e6b4-162304461&mc_cid=606fd7e6b4&mc_eid=3e4d1f2edd

If I ever desire more power or shopping for amps, will definitely consider them.

I may buy his MP-3 tube pre when i make up my mind about dealing with tubes again. It lseems like a nice piece in the price range of what i’m willing to pay for w.r.t tube preamps (to try pairing with my Technics SU-R1000 and flavor it up a bit)...

http://www.atma-sphere.com/en/mp-3.html

(Not interested in the greatness of Class D-iddly that has apparently put every Class A and AB under 100k in the dust these days!!)

If he can beat my Class triple D SU-R1000 one day on innovative engg (umpteenth level out the wazoo), i ’ll give it a listen....But, when i just look at his D with the chassis open, it ain’t looking like much to me. May the GAN flow like the Niagara however and make y’all blissful.

GAN miracle vs Technics, it just ain’t adding up on what you’re getting for the price! Funny enough, even that ~10k honestly priced engineering extravaganza Technics gets hammered by a whole lot of simpler Class A designs and no Class D-iddly under 100k i know of got crack engineered as good as the Technics (to nullify the cons of Class D-iddly).

Class A vs the rest - A interesting discussion by the grand Schiit Lords at Schiit Audio...

https://www.youtube.com/watch?v=_rSQCqqTk4E&t=459s

This is how the internals of 1930 computers looked. Compare that to the internals of today's desktops/laptops/servers/super computers

That's it...I just got meself a brilliant business idea. My Class D-iddly amp company will, hereby, be known as "Exo-sphere", i.e., what you hear from my amp will launch you all the way past the atmosphere into the exosphere itself. You will be a lick away from feeling the eternally blakkkk background of space when you listen to my D-iddly amp.

I am gonna buy some kits from aliexpress for a 150 bucks with shipping. I will sprinkle some sodium chloride inside the chassis, light some incense and do a shamanistic dance with it. Thereafter, I will gorilla glue a fake gold label called "Exosphere" on it.

Price = 5700 USD, Exosphere profit per unit = 5550 USD

Thereafter, i will create a hidey account and play the pied piper for my product for a few months. I will pretend that i'm a completely ecstatic customer overjoyed with a Exosphere Class D-iddly amp. I will also pay a couple of other forum pied pipers to sing eternal ecstatic prose about my D-iddly amp.

As all you boys hand me your hard earned cash and empty your retirement accounts, I will laugh all the way to the bank and cash the checks selling Exosphere amps for 5700 a pop. When i see my cousin/my brotha from anotha motha (you know who) snickering away, cashing his checks at the bank, we will hug, hold hands, laugh together and get sloshed at the bar next door to the bank....Oh yeah...baby....Oh yeah...early retirement, here i come....

@deep_333 

Thanks for the pics of the Technics innards. Have you hear their newer model G700 Mk 2?

No, i have not...not interested in that one. It has great reviews though. I specifically needed the SU-R1000's 300W into 4 ohms (without space heater amps deployed) for one of my speakers.