Class A/AB vs D -- Is it Audible in 2021?

[watchnerd]

So if I don't care about heat, cost, size, or efficiency, or SINAD differences that are below the audible threshold....

Is there any real audible difference between Class AB or D?

I've read some claim that Class D has "better bass control".

Is there any truth to this?

I think I've heard this, but perhaps it's just placebo / cognitive bias after being heard to listen to it.

I've also heard some claim that A/AB (well, A, mostly) has "wider sound stage" or "warmer" or "more analog".

Which, *maybe* I've heard, but, again, can't rule out cognitive bias, once again.

Is there any objective truth to any of these stereotypes?

Or, really, do they both sound the same when operating way below redline?



Full disclosure:

My "big rig" passive spaker amp is a Devialet Expert 400, which 'ADH", some kind of A/D hybrid, while all my active speakers use Class D. I can't say I've noticed some kind of measure difference...maybe the Devialet sounds a tad 'wetter'. Maybe.

 

[RayDunzl]

Or, really, do they both sound the same when operating way below redline?

Audio Buddy and I went to the audio show twice.

Despite all the different electronics being hawked, it wasn't long before we came to the conclusion that the only thing we were hearing was speakers and recordings.

 

[Doodski]

I can't vouch for class D because I have not to my knowledge heard one. As per A/AB I've handled hundreds of different models of A/AB and I only found one class A amplifier that sounded different and I attribute that to it's output linearity.

 

[pma]

@watchnerd Your question is too general and as such is pointless. You always need to speak about the designs and products namely, taking their design and specs into account.

 

[watchnerd]

@watchnerd Your question is too general and as such is pointless. You always need to speak about the designs and products namely, taking their design and specs into account.

You've said similar before.

Can you provide examples that would create a contrast between them?

 

[watchnerd]

Audio Buddy and I went to the audio show twice.

Despite all the different electronics being hawked, it wasn't long before we came to the conclusion that the only thing we were hearing was speakers and recordings.

Not even speakers, recordings, and rooms?

But it sounds like a 'no audible difference' on the amp front.

I've heard a lot of Class D fans talk about how the damping factor is higher = better bass.

 

[JohnYang1997]

https://www.audiosciencereview.com/...-measurements-lm4562-option.19155/post-628954

So yes for the most part, including ICE, some TI some infineon and other implementation that don't have post filter feedback.
Basically no for ncore, purifi stuff.
On the other hand low feedback poor class A AB designs are also causing differences. So I already assume the blameless class AB designs.

 

[RayDunzl]

Can you provide examples that would create a contrast between them?

My Contrasting Case:

I have Krell Class A (if they really really are) driving the Martin Logans, and a Class D chip (if it really really is) driving the JBL LSR 308.

At moderate levels, and not in the sweet spot (where the room effects becomes a tell), like here at the desk in the right rear corner, or prone on the couch entering or exiting nap mode, if I have forgotten which is playing after playing around, I have to look at the indicator lights, which are not a definitive answer to which is active, and then it is necessary to grab the remote to straighten things out.

So, in my limited case, to my deaf ears, nothing distinguishes one set of amplification from the other at a watt or so of listening level.

 

[RayDunzl]

Not even speakers, recordings, and rooms?

Other than a Goldilocks Trio (too big, too small, just right) of Conference Rooms with the Unobtanium Speakers and kit (Von Schweikert, Magico, MBL) on display, all the rooms were the same at the hotel, an Embassy Suites that was originally condos and converted. There were mirrored floorplans, but otherwise all the same. Walk from the hallway into the living room past a tiny kitchen area, with a bedroom and large bath through a single door to the side.

Some vendors would set up on the longer wall, others on the shorter.

Those differences didn't illuminate differences in the electronics.

 

[Alice of Old Vincennes]

@watchnerd Your question is too general and as such is pointless. You always need to speak about the designs and products namely, taking their design and specs into account.

It is a very specific question. You just don't want to face the answer.

 

[Alice of Old Vincennes]

My Contrasting Case:

I have Krell Class A (if they really really are) driving the Martin Logans, and a Class D chip (if it really really is) driving the JBL LSR 308.

At moderate levels, and not in the sweet spot (where the room effects becomes a tell), like here at the desk in the right rear corner, or prone on the couch entering or exiting nap mode, if I have forgotten which is playing after playing around, I have to look at the indicator lights, which are not a definitive answer to which is active, and then it is necessary to grab the remote to straighten things out.

So, in my limited case, to my deaf ears, nothing distinguishes one set of amplification from the other at a watt or so of listening level.

I think your ears are just fine.

 

[ShadowFiend]

As a diyer and sometimes customer, here is my opinion.

1. "Class D have better bass control" is a false statement in science point of view, but a somewhat valid one in commercial device.

Bass control is the combination of high damping factor and output current capacity of amplifier at the low load. Problem is speakers right now, especially bookshelf, have low sensitivity and low impedance with horrible phase in bass region. So the amplifier must be capable to deliver huge current at low impedance. Many amplifiers, especially tube amp or wimpsy amp, are not capable of doing that and reach a point of clipping at that moment. And with nature of clipping, the high THD effect caused by clipping will last a small period of time before it going back to normal. Class D amp, especially the good one, does not suffer from this effect. And that can be a different people heard.

In addition, class D like Hypex uses much more negative feedback than the normal class A/AB out there (Benchmark or Halcro or Soulution aside), so naturally class D amp will have lower distortion than the normal class A/AB on the market. Because of that reasons, the class D will have better bass control than the vast majority of class A/AB in the market. But if you have class A/AB amp with huge amount of current reserve and using good amount of negative feedback, their bass control to your speaker is the same

 

[MakeMineVinyl]

I think its highly dependent on the speakers (and room) which the amp is driving. You can bet your ass that there would be differences in sound on my extremely efficient horns which have active crossovers, but for 99.99% of people with 'normal' speakers, I doubt there would be any difference.

 

[Alice of Old Vincennes]

As a diyer and sometimes customer, here is my opinion.

1. "Class D have better bass control" is a false statement in science point of view, but a somewhat valid one in commercial device.

Bass control is the combination of high damping factor and output current capacity of amplifier at the low load. Problem is speakers right now, especially bookshelf, have low sensitivity and low impedance with horrible phase in bass region. So the amplifier must be capable to deliver huge current at low impedance. Many amplifiers, especially tube amp or wimpsy amp, are not capable of doing that and reach a point of clipping at that moment. And with nature of clipping, the high THD effect caused by clipping will last a small period of time before it going back to normal. And that can be a different people heard.

In addition, class D like Hypex uses much more negative feedback than the normal class A/AB out there (Benchmark or Halcro or Soulution aside), so naturally class D amp will have lower distortion than the normal class A/AB on the market. Because of that reasons, the class D will have better bass control than the vast majority of class A/AB in the market. But if you have class A/AB amp with huge amount of current reserve and using good amount of negative feedback, their bass control to your speaker is the same

If amp avoids clipping I doubt one can discern difference. Crown XLS will not clip.

 

[Alice of Old Vincennes]

I think its highly dependent on the speakers (and room) which the amp is driving. You can bet your ass that there would be differences in sound on my extremely efficient horns which have active crossovers, but for 99.99% of people with 'normal' speakers, I doubt there would be any difference.

Then why deal with it? Just means you need over priced amp.

 

[MakeMineVinyl]

Then why deal with it? Just means you need over priced amp.

If you're referring to what I ended up using for driving my horns, it cost less than either the class A/B or class D amp.

 

[ShadowFiend]

2. The statement "A/AB (well, A, mostly) has "wider sound stage" or "warmer" or "more analog"" is also true, but not because of the scientific reason.

Class A amplifiers, when they are in class A, eliminate the worst distortion, "crossover distortion". So many designers use that characteristic not to reduce distortion to lowest level, but to control the distortion profile. With lower level of NFB, therefore lower open loop gain and fewer component, it is easier to manipulate the distortion profiles. Nelson Pass, for example, said that the negative phase of second order distortion at 0.1-1% will cause the soundstage to deeper and sound smoother. I have build his diy preamp (ACP+) and confirmed that when comparing to direct path to my Hypex NC400. And that is an only one effect has been noted, there are probably more.

 

[Blumlein 88]

John Yang is telling it right. Some class D is audible from filter issues. The better later designs are exemplary. Same for best of class A and A/B. Ultimately the best of class D can simply be the best of them all.

 

[Alice of Old Vincennes]

If you're referring to what I ended up using for driving my horns, it cost less than either the class A/B or class D amp.

Mysterious.

 

[ShadowFiend]

My Contrasting Case:

I have Krell Class A (if they really really are) driving the Martin Logans, and a Class D chip (if it really really is) driving the JBL LSR 308.

I think you should be disappointed that your Krell amp is not a full class A by any means. Its true class A wattage is a round 60-65W max