Class A/AB amplifiers value

Hello there,
These days I'm a bit bothered with the value of the class A/AB amplifiers.
To be more precise, why are the class A/AB amplifiers the only one considered as an "audiophile" choice of amplification when they measure worse compared to the nowadays class D (hypex, ICEpower) amplifiers in both S/N ratio, THD, and power.

I understand that in the past the class D amplifiers couldn't handle the distortion in the high-frequency region, but today's modern designs don't have any problems with distortion in any region at all. So, what's the true value of the class A/AB designed amplifiers?
Why do they cost more when they measure worse?
How are they supposed to sound better when they measure worse?

 

Give an example of 'measure worse'.
I have not found that to be the case.
They are typically comparable.
They are cheap to build, basically an A/D converter switching igbt's.

 

Many people consider some of the recent Class D amplifiers to be of audiophile quality. I'm one of them.

 

People like amplifiers based on their sound not their measurements. To many, Class A especially, but also Class AB sound better than Class D.

 

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Most biases towards amplifiers come from prior experience. So 15 years ago people compared a Class D amplifier to a Class A amplifier the class A amplifier sounded much better. Perhaps they auditioned 3-4 class D amplifier brands and disliked the sound so a "stereotype" forms that gee I heard 4 class A amps and all 4 sounded fantastic and I heard 4 class D amps and they all stunk.

But that was 15 years ago. And when you have formed the view that class D sucks there is a good chance you are not spending a lot of time with them. Meanwhile, as you note, they have improved over the years.

But this is the same argument with CD in the 1980s - it sucked. But the players and recordings were often the problem. So 30 years later CD players had greatly improved and so did the mastering for CD and the gap narrowed significantly.

Indeed, so has class A and A/B SS over the years as well. I would not put all your eggs in the measurements basket - plenty of review magazines do plenty of measurements and the reviewer himself then proceeds, oftentimes, to buy gear for his own home that is say a Tube amplifier or middling measuring speakers. Even John Curl noted that he designed a speaker that measured really very well but didn't sound as good as other speakers - so he said of himself that he was a bad speaker designer. Measured great.

 

IMHO digispeakers are the future of best sound. There is little doubt in my mind. Others are just slow in getting started.

 

Maybe passive crossovers, speaker cables, interconnects, and metal/metal interfaces improve sound?

 

Even in the live music/musician‘s back line gear, Class D is still viewed as the redheaded stepchild because the offerings 10~15 years back were not so hot. It’s been a tough uphill battle to shake that reputation since.

The thing that’s helped Class D the most is along with neo drivers, rockers with aging backs welcome the lighter load in/out.

 

Like everything else in audio, probably best to take each amplifier on a case by case basis. By listening. Not sure what measuring is going to tell you about how it sounds or what it is worth to you.

 

It's almost as if the speakers being driven are a slight consideration as to what might work best with them.

How does today's Class D handle a set of Thiels, Quads, or Magnepans? Or even Dynaudios or any speaker that performs better with gobs of current?

Seems like something a blanket statement isn't quite prepared to handle overall.

The most recent experience I have with them is the factory upgraded NuPrime ST-10 (model number off the top of my head, I may have that wrong) on my Dyn Focus 260s.

I've had 4 or 5 different amps on these speakers and they sound nothing alike in any case. Unfortunately for me in my room and system and tastes, the NuPrime was the least engaging, the least dynamic, and by far the least amount of bass control and quantity.

 

Apparently well enough to sell me his Innersound monos for 3 bills. See 3rd link above post 187 to see Pat's "digi-infrasonic project".

 

With class d I just don't see the value for my money sometimes. It's literally a hypex module in a box. With class a/ab you get a big heavy amp with big power transformers, heatsinks, big capacitors, etc. You can really appreciate what your money went to. Also class d just kinda lacks in "heart and soul" appeal to me. It seems more cold and analytical, like it's meant for a utilitarian professional purpose rather than intimate enjoyment of music.

 

I'm in my early 50s, so from my teens when I first got into hi-fi until a year or two ago, I was all about Class A/AB. The hallmarks of amp quality for me were similar to what @Razakoz notes: massive linear power transformers (preferably toroidal), large capacitors, and a couple dozen pounds' worth of metal casing and heat sinks.

But the amp world has changed radically in the past few years, and now there's no single topology (Class A/AB, D) that's uniformly better than others. There are very good amps available of both types for reasonable prices, and some truly excellent amps of both types available for higher, though not stratospheric, prices.

In terms of low-distortion, low-noise watts per dollar, however, Class D rules the roost. Switching noise and high-frequency linearity are problems that were solved a few years ago in the form of the last two generations of the Hypex NCore amps and the Purifi amps. And Class D amps don't have massive power supplies and heat sinks because they don't need them. As to where the money is going, the beauty of Class D is that some of the money isn't going anywhere - it's staying in your pocket.

Right now, Hypex and Purifi are where it's at if you want excellent measurements, decent power (about 80-250 real-world watts per channel into 8 ohms), excellent current handling, first-rate speaker and circuit protection, and a high damping factor for about $600-$1,000 per channel (depending on maker and associated features). If you believe in measurements to the extent that you believe a 102dB SINAD (signal over noise and distortion) measurement is better than an 86dB SINAD and that a 10-15dB improvement in Intermodulation Distortion is meaningful, then Class D owns the mid-priced hi-fi segment performance-wise. That could of course change in the future. But right now IMHO you'd be hard pressed to equal or better Class D's combination of performance and wattage in the $1000-$2000 range for 2 channels.

If you want to drop $3,000 to $5,000, by contrast, then you can get a Class AB Benchmark AHB2 (albeit that one uses a switching power supply) or a Bryston 2.5b3 and you're good to go.

Finally, one reason Class D is more affordable has little to do with the actual components or bill of materials for a Class D vs Class A/AB amp. Instead, it has to do with the business and distribution models. Class A/AB is pretty much the exclusive realm of conventional manufacturers and brands. Class D, by contrast is mostly modules sold to whomever wants to buy them to make and sell amps, so you get a lot of new and smaller players who build no-frills power amps and have small marketing budgets and staffs, and sell them at relatively small markups. If you want to get a sense of how much markup is built into a typical Class A/AB amp, you can compare the going rates for Hypex and Purifi power amps from the smaller European companies with the prices of amps based on the same modules from NAD. NAD amps often have more features or more refined-looking casework, but they measure no better than the little guys' amps - and they often in fact measure worse because of whatever NAD adds to the circuit - and the prices are outrageously high relative to the little guys.

 

...and here we have the answer to the OPs question in a nutshell! That even if a Class D amp is excellent, it simply won't have sex appeal to some. (To others, like myself, there is a different kind of sex appeal in the lightness and efficiency-which by the way means ability to get more power out of a wall outlet). To others, it may seem "digital"="Satan" even though very very are actually digital at all ha ha,

Now I recall at a local Audio Engineering Society talk one Class D designer declaiming that you calculate out what you need and simply do not need bigger capacitors and such, it is of no use. Even so a great Class D touring amp won't be as impressive feeling as a 135 lb old-school Crest or whatever.

Yes, at the dawn of Class D there were designs perhaps not up to the AB standard. In car audio I recall the Infinity, which to try and be as impressively compact as possible had little heatsinking and had a tendency to over heat. Of course ANY early technology is not fully realized. 40+ years on, Class D has had a lot of development.

By now, I firmly feel that just as in so many other areas of audio, the technology is less important than the skill of the designer. (Think multibit vs. 1-bit DACs, belt-drive versus direct-drive, coaxial versus not, etc etc etc).

 

Here's a more expensive Class D offering - more expensive because it's a monoblock (so you need two for stereo), and it delivers at least 665 continuous watts into 8 ohms. But if you need that kind of power, there's no other option I'm aware of at this unit's price of $2200-2500 per channel that delivers the distortion and noise performance of this unit.

Here's a detailed measurement-based review, and also a detailed look inside so you can see what the inside of a well-built megawatt-class Class D amp looks like:

Review: Apollon Hypex NC2K Monoblock Amplifier Review

A Look at the Internals: Apollon Hypex NC2K Amplifier Teardown

 

I'm grateful to class D for what it can accomplish within certain space and thermal constraints, but to my ears it's never superior to a good Class A / AB design (especially A when you can get it) - My car for example, it has a silly number of speakers, I think 12 or something like that, each one with it's own class D amp driving it, that I'll likely never have to worry about it failing. The car is already a less than ideal listening environment so any distortion class D presents isn't going to be more noticeable than road noise. Got a massive space to fill with lots of sound? Class D crown amps are a god send for doing this at a reasonable cost and footprint. So they have their purpose. That said, I'd never consider one for my main listening room. The reality is the power supply is switching on and I've always found it to be more fatiguing and less pleasant over long periods of time, and I also find Class D struggles with large dynamic bursts without distortion. It has it's applications, it's great tech, but to my ears it never sounds better than a good Class A or AB design.

 

The best measuring amp in existence is actually class AB and it happens to operate cooler than many D designs. So one could argue that THX AAA technology has made class D obsolete.

 

Crown Class D amps - and other similarly designed pro-market and car-audio Class D amps - are designed for maximum power and environmental ruggedness per dollar. They achieve this at the expense of performance. It's nothing to do with Class D switching noise or limitations of the Class D topology. The Crown amps simply have much higher noise and distortion than the Hypex and Purifi designs.

One can argue that only if one is interested in headphone amps (where there are affordable THX AAA options that are truly "buy one and you never have to buy another one for the rest of your life" products) - or if you are interested in a speaker amp and price is not a factor. The best measuring amp in existence - the Benchmark AHB2 - is $3000, achieves its best performance at its lowest gain setting, which is something like 12dB, and has a max gain setting of less than 24dB, compared with the typical 29dB of most Class A/AB power amps. If you want to get 29dB gain out of the Benchmark amp, you have to buy two and run them in bridged mono mode.

So I agree with you - even used as a single stereo unit at its highest (and worst-measuring) gain setting, the Benchmark is a world-beater - it's amazing, But it's also 1-1/2 to 2 times as expensive as various high-quality Class D power amps that deliver more gain, in some cases more power, and distortion and noise that are inferior but still in the same ballpark and beyond the threshold of audible transparency.

Not to mention, the Benchmark's switching/current regulated power supply (which is basically, as far as I understand, what makes an otherwise AB amp a THX AAA amp) is precisely what a lot of Class A/AB aficionados say they can't tolerate - as per @cliff_forster 's comment quoted just above.

In addition, like all very low-distortion amps, the Benchmark employs significant negative feedback, and the mythology of "pure" Class A amps is that feedback makes the sound brittle. So while the Benchmark is Class AB, it achieves its amazing performance by using technologies (combined with unusually low gain to give it a little extra edge) that make it a non-starter for many folks who are dedicated to Class A/AB over Class D.

To be clear, I don't subscribe to those views - I have no problem with well-designed, properly implemented switching power supplies, and well-implemented negative feedback. I'm just saying that because of those design features and its price, the Benchmark - and THX AAA in general - is not IMHO a good example to support the claim that Class D has been rendered obsolete when it comes to speaker amps.

Now, if Benchmark were to come out with an AHB3 or some such, and keep the AHB2 in their model line but lower the price to, say $1,800-2,000, then I would readily agree with you - there would be no point in saving 10-20% with a similar Class D amp when you could get the King of the Hill for that kind of price. But so long as $3,000 is the floor for that kind of performance in an AB amp, there is still very much a major role for Class D.

 

If more manufacturers license the THX tech we’ll probably begin to see similar amps at lower prices, which would indeed make class D obsolete IMO. One reason the AHB2 costs what it does is because it’s unique in the market. Its BOM is probably less than many of the $1K class D amps.

I think the switching power supply is a moot point when comparing it against a PWM class D amp. If a class A owner takes issue with a SMPS, they’re certainly not going to want the switching amplification circuitry of class D, even if it has a linear PS.

As for the gain, I’ve never needed anywhere close to 29db from an amp, with any speaker or source. Most amps have far too much gain considering the high outputs of modern source components.

 

Being a sound producing device I would rather evaluate with my ears instead of my eyes.

 

First Watt Class A do not lose value. I am not sure, but $2K used may be the value.

 

There are two main problems with class D:

1. They need output filter. That filter may misbehave when speaker impedance has large variation in value and phase. You need to make sure your speakers are compatible with your amplifier. That is why class D amplifiers are best used in active speakers - there filter is optimized for driver used in that one particular speaker and crossover is done before power amplifier.
2. Switching speed of modern class D amplifiers is too low - usually in 400-500kHz range. Compare that with DSD audio encoding at 2.8MHz, which is considered entry level. Before I buy class D amplifier for anything other than subwoofer, I will wait until I see one with switching speed equivalent to DSD128 encoding - 5.6MHz. Considering state of high power electronics today, it may take another 10 years to get there.

 

I lived with the Marantz PM-10 for almost the last 2 years and just replaced it with the Gato Audio Amp-150 AE (Class AB). The Gato sounds like real musicians playing real instruments. Chalk it up to experience.

 

Class D is the "Beyond Meat" of audio.

It sounds all good for you on paper, but those first attempts were...less than satisfying.

So, as mentioned above, it's an uphill battle to change perception.

After that, "Class" should not even be part of the discussion, imo.

Product choice should be cost and performance(the actual listening kind).