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" Class D " and the virtues of, a guru roundtable discussion setup by Absolute Sounds


georgehifi
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The Absolute Sounds Guide to Audio Electronics contains an interesting feature, the "Amplifier Designers Roundtable". Interesting views on the subject of Class D amplification:

Is Class D competitive with linear designs in sound quality,
and if not, will it ever be?

 

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."

John Curl (Parasound, CTC, Vendetta Research, Constellation)

"Some version of hybrid Class A/D looks like the future in optimum audio design."

Cyrill Hammer (Souloution)

"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)

"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 (Threshold, Passlabs)

"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 Reiss (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."

Jeff Rowland

"I consider Class D to be highly competitive in the present, and to offer an evolutionary pathway of audio design that may produce even more astonishing results in the future."

http://media.avguide.com/BG_Audio_Electronics_2012.pdfSee More

 
 
 
Thorsten Loesch 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 DAC's #" 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 90’s reviews of timeslicing dac’s. 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 “full scaleâ€, if they would be dac’s. 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 Levinsons 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.


Thorsten Loesch 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.
 
Cheers George

 

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George, thank you for sharing those statements from audio luminaries.

 

I suggest those of us whose reason for listening to music is to enjoy the performances and the listening experience, do not go anywhere near digital - we prefer analogue source and conventional amps. ;)

 

Regards,

 

Andy

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I suggest those of us whose reason for listening to music is to enjoy the performances and the listening experience, do not go anywhere near digital - we prefer analogue source and conventional amps. ;)

 

Digital source and "non-conventional" class D amps here and I thoroughly enjoy them.

You sound like a snob :)

Edited by Satanica
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+1 to Newman.

 

Class D amps are analog  - but utilise "switching" output devices.

 

Digital Amps are DACs with an amplified output stage which is achieved via a low pass filter eg NAD 390 DD.

 

Not suggesting for a moment that the luminaries above have got it wrong... but I do question some of the language - particularly references to Class D being effectively an A to D and D to A in a box.

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Digital source and "non-conventional" class D amps here and I thoroughly enjoy them.

You sound like a snob :)

 

Ah! but if he were listening to you through a class D amp, you'd sound like a robot.......apparently.  :lol: 

 

The only class D amps I ever heard were the Bel Canto somethings when WAR Audio had them, In his digital system they sounded pretty good, but I guess the real puddin' proof is in the longer term.

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I think one of he key points I take from the above comments is that they seem to be talking about the "super high end" . For me, it is highly unlikely I will ever have an amp from that rarefied air. Coming back to the "mid market" they also refer to, I think the differences are much less pronounced. In addition, the ancillary equipment, sources and speakers in this so-called mid-market may or may not be capable of differentiating between the different classes of amps. Ultimately, in the market I play in, class D can provide a very good, and musical solution. If you want to bend the sound or introduce some pleasing distortion, throw In a tube pre-amp. I am yet to do it, but from everything I have read, proper positioning and room treatments will have a much bigger impact on sound quality than the difference between different classes of amp. Of course, this is all IMHO and YMMV

Edited by markm1111
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Ah well They never bothered obviously to speak to the doyen of Class D Amp Design Jon Ulric of Spectron--they have garnered some fine kudos-while I'm not  a fan of the ilk completely his efforts in this field were exemplary.

 

I have owned Jon's previous effort the Infinity Switching Amp of the early 80's and could see/hear the potential

 

With that pedigree, his current designs are the ones I'd take a listen to if savouring to purchase similar products.

 

The others purporting Class D salvation are merely touching the edges as yet.

 

Willco

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I think it depends on the music.

 

Not sure if a lot of audiophile wankers crank out the death metal on a regular basis but from my experience SS just cant do it, all glare and tizz, and tubes get too muddy down the bottom and it all gets blurred

 

The Bel Cantos give firm controlled bass, and smooth out the top enough to make it bearable.

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I think it depends on the music.

 

Not sure if a lot of audiophile wankers crank out the death metal on a regular basis but from my experience SS just cant do it, all glare and tizz, and tubes get too muddy down the bottom and it all gets blurred

 

The Bel Cantos give firm controlled bass, and smooth out the top enough to make it bearable.

I own a valve amp and can play death metal without muddy bass not all valve amps are the same 

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I think it depends on the music.

 

Not sure if a lot of audiophile wankers crank out the death metal on a regular basis but from my experience SS just cant do it, all glare and tizz, and tubes get too muddy down the bottom and it all gets blurred

 

The Bel Cantos give firm controlled bass, and smooth out the top enough to make it bearable.

 

I suggest "audiophile" & "death metal" in the same sentence ... is an oxymoron! :P  I suggest Class D amps are purrfekt for death metal? :thumb:

 

Regards,

 

Andy

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I own a valve amp and can play death metal without muddy bass not all valve amps are the same 

 

Indeed

 

At the recent GTG in Canberra all the valve guys there liked the Arion Class D I bought along - many said it was the best SS they had heard.  But they were valve guys and liked the modified and reconditioned Leak that was there best (as did I).  The consensus was the Leak was the best amp there followed by the Arions - and on that particular system that was my view as well.

 

Thanks

Bill

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Class D is the future of amplification - full stop -  the audiophile snobs of this world are probably right a truly high end Solid state will beat any class D hands down.  High end comes at a cost they draw significant power, overweight, take up room and cook like an oven.

 

Class D beats any Solid state amplifier in its price range and possibly double or more.  Specs and graphs do not tell the full story.

 

I am done with Solid state will never own another SS amp.  I have owned three Class D amplifier. Love my Belcanto's but about to purchase a D Sonic 1500W into 8 Ohms.

 

Tubes lovers are fully understandable as sometimes a little valve coloration in the sound can be very satisfying and musical. Tubes and Class D are a nice combination.

 

We are in a new golden era of audio and we should appreciate and embrace this new technology as it is truly remarkable.

 

It is also on a path of improvement so lets wait and see what the next few years brings.

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I own a valve amp and can play death metal without muddy bass not all valve amps are the same 

I don't normally listen to death metal, but I can really imagine it being cranked out of some coffin sized box speakers in a really small dark room with cool running class d amps (cause the air circulation is not too good in here). R.I.P.

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Class D is the future of amplification - full stop -  the audiophile snobs of this world are probably right a truly high end Solid state will beat any class D hands down.  High end comes at a cost they draw significant power, overweight, take up room and cook like an oven.

 

Class D beats any Solid state amplifier in its price range and possibly double or more.  Specs and graphs do not tell the full story.

 

I am done with Solid state will never own another SS amp.  I have owned three Class D amplifier. Love my Belcanto's but about to purchase a D Sonic 1500W into 8 Ohms.

 

Tubes lovers are fully understandable as sometimes a little valve coloration in the sound can be very satisfying and musical. Tubes and Class D are a nice combination.

 

We are in a new golden era of audio and we should appreciate and embrace this new technology as it is truly remarkable.

 

It is also on a path of improvement so lets wait and see what the next few years brings.

Cada may i correct you about tube colouration all electronic equipment including tubes and transistors class a,ab or d has colourations.

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Class D is the future of amplification - full stop -  the audiophile snobs of this world are probably right a truly high end Solid state will beat any class D hands down.  High end comes at a cost they draw significant power, overweight, take up room and cook like an oven.

 

Class D beats any Solid state amplifier in its price range and possibly double or more.  Specs and graphs do not tell the full story.

 

I am done with Solid state will never own another SS amp.  I have owned three Class D amplifier. Love my Belcanto's but about to purchase a D Sonic 1500W into 8 Ohms.

 

Tubes lovers are fully understandable as sometimes a little valve coloration in the sound can be very satisfying and musical. Tubes and Class D are a nice combination.

 

We are in a new golden era of audio and we should appreciate and embrace this new technology as it is truly remarkable.

 

It is also on a path of improvement so lets wait and see what the next few years brings.

 

 

You will excuse me if I don't agree.

 

Class D is nothing more than a compact fluro light replacing an incandescent globe. It is indeed energy efficient but if it's the way forward then I want to go backward or stay in the present.

Nice to read that you are loving it though, diversity is what this gig is all about :)

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+1 to Newman.

 

Class D amps are analog  - but utilise "switching" output devices.

 

Digital Amps are DACs with an amplified output stage which is achieved via a low pass filter eg NAD 390 DD.

 

Not suggesting for a moment that the luminaries above have got it wrong... but I do question some of the language - particularly references to Class D being effectively an A to D and D to A in a box.

 

Displaying my ignorance here, are you saying that digital amps are not Class D?

If so, how does the amplified output stage amplify - is it A/B ?

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And here I am playing 24/192khz rachel podger Vivaldi on $50 class D (that's for 4 channels). Yet so sublime :)

 

Get the speakers right, and I mean only a piece of wire between the drivers and amps... no nasty inductors, capacitors.... and the amplifiers become moot point.

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And here I am playing 24/192khz rachel podger Vivaldi on $50 class D (that's for 4 channels). Yet so sublime :)

 

Get the speakers right, and I mean only a piece of wire between the drivers and amps... no nasty inductors, capacitors.... and the amplifiers become moot point.

If only all of us where so easily impressed  ;)  your very lucky gainphile 

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Displaying my ignorance here, are you saying that digital amps are not Class D?

If so, how does the amplified output stage amplify - is it A/B ?

 

D is not for Digital….. but Digital (amp) is D.

 

Brevity…. don't ya love it?

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Thanks It amuses me sometimes the unwillingness to change the basic topology of the whole system for a clear gain.

Almost like trying to make a 2 cylinder engine go fast in motorcycle world, where clearly 4 cylinders are better. The ducatis and harleys for example.

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2 cylinder dukes pushed the 4 cylinder **** off the superbike scene.

 

Sorry OT

 

[edit: mods or system deleted the word j-a-p-s from the above. I was referring to motorbikes not people of course]

Edited by Newman
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