ATI Battle Class AB vs Class D Amplifier Shootout

[lovinthehd]

For a subjective review I think this one is one of the best (if not the very best) I have read. I thought it was objectively subjective.

Yes, as far as this subjective review goes I really have no complaint....just little use for such.

 

[Irvrobinson]

I'm not looking for an amp, but I will remember that the ATI version of Hypex Class D designs, such as the AT522NC, got good marks from Gene.

Gene didn’t write the review. RichB did.

 

[dave-t]

I just order a AT527NC and am anticipating delivery on Tuesday the 28th. I was going back and forth between At4007 Signature series ( I have been a class AB guy for. long time) and the At527NC. I was told by multiple people The At4007 thrives when used for music, however I am 99% home theater so I went Class D NCore. I was also told that they are very very close if not the same for home theater. I also spoke to tech support at ATI and was told that a At4007 would call its own dedicated 20amp line because of ll of the power it draws. My last statement was really what tipped me towards the Class D over the class AB

 

[RichB]

The view that all amps sound the same driving all speakers when operating within their limits is compelling.

Great care and many hours were spent auditioning these amplifiers and, my finding is that these two amps were easily distinguishable in my systems.

It is worth reading the Sound and Vision interview with NCore designer (Bruno Putzney):

https://www.soundandvision.com/content/bruno-putzeys-head-class-d

S&V: Conventional wisdom says a great amplifier has no sonic character of its own and, beyond boosting the signal level, is transparent in the audio chain. But does the nature of high-quality Class D amplification—perhaps through the absence of distortions found in other circuit topologies—produce a particular sonic signature or specific attributes you could describe?
BP: Well, if the amplifier is truly great that’s absolutely right. Sonic signatures are what you get when you approach the same ideal from different angles. There are a few distortion mechanisms conspicuously missing in Class D, mostly those related to the input stage of a Class A(B) solid-state amplifier and nonlinear capacitances. Those are also missing in valve [tube] amplifiers so it’s quite common for people to notice that a Class D amplifier is somehow reminiscent of valve amplification in terms of “sweetness” for want of a better word.
I’ve heard several reports of valve aficionados ditching their glassware and switching to Ncore. All I can conclude from that is that those people clearly weren’t actively seeking the distortion of valves as many believe, but instead had a legitimate beef with certain sonic aspects common to most solid-state designs. That’s one thing I have to explain again and again to my fellow doubters: when audiophiles report a particular listening experience, that experience is real. Trust that. Just don’t trust the explanation they proffer.
Read more at https://www.soundandvision.com/content/bruno-putzeys-head-class-d-page-2#MUOWy3PiLteEB8S7.99

Taking a zero-based view of the facts, most of us are used to Class A/B amplifiers (some with sonic signatures).
Is it really so surprising that a completely different technology, lacking those, and perhaps adding others can sound different driving real loads?
After experiencing both amps, I am not surprised. From my reading of the Bruno Putzney interview, I don't think he would be surprised either.

- Rich

 

[RichB]

Agreed. Without measurements this review isn’t really useful.

Yes but, it is like seeing someone in their underwear, it just can't be unseen

- Rich

 

[Irvrobinson]

The view that all amps sound the same driving all speakers when operating within their limits is compelling.

Great care and many hours were spent auditioning these amplifiers and, my finding is that these two amps were easily distinguishable in my systems.

It is worth reading the Sound and Vision interview with NCore designer (Bruno Putzney):

https://www.soundandvision.com/content/bruno-putzeys-head-class-d



Taking a zero-based view of the facts, most of us are used to Class A/B amplifiers (some with sonic signatures).
Is it really so surprising that a completely different technology, lacking those, and perhaps adding others can sound different driving real loads?
After experiencing both amps, I am not surprised. From my reading of the Bruno Putzney interview, I don't think he would be surprised either.

- Rich

I’m just not buying it, Rich. The distortion Putzney is talking about in a Class AB amplifier like the ATI is more than 90db below 1W, but you’re saying the difference is obvious. Either noise is a lot higher, or distortion is a lot higher, or some other effect is involved, like differing levels or a non-flat frequency response. Your results need the proof only measurements can provide.

 

[RichB]

I’m just not buying it, Rich. The distortion Putzney is talking about in a Class AB amplifier like the ATI is more than 90db below 1W, but you’re saying the difference is obvious. Either noise is a lot higher, or distortion is a lot higher, or some other effect is involved, like differing levels or a non-flat frequency response. Your results need the proof only measurements can provide.

Dynamic performance into a speaker load is my hypothesis.

Measurements are an anti into the game and then I expect that Class A/B should be similarly good but the implementation of protection and effectiveness of negative feedback can vary (again playing music into a speaker).

Benchmark has their statements on audibility but I don't think you are buying those either

By the way, you might as well also doubt that the AHB2 sounds different from the others as well under the same conditions.

- Rich

 

[Verdinut]

I just order a AT527NC and am anticipating delivery on Tuesday the 28th. I was going back and forth between At4007 Signature series ( I have been a class AB guy for. long time) and the At527NC. I was told by multiple people The At4007 thrives when used for music, however I am 99% home theater so I went Class D NCore. I was also told that they are very very close if not the same for home theater. I also spoke to tech support at ATI and was told that a At4007 would call its own dedicated 20amp line because of ll of the power it draws. My last statement was really what tipped me towards the Class D over the class AB

For the AT4007 to require a 20 amp dedicated circuit, it all depends on the sensitivity of the speakers, the average SPL and the listening distance from the speakers. I'm sure that for most audiophiles, who want to keep their hearing acuity, and have an average size listening room and speakers with moderate and higher efficiency, a 15 amp circuit would suffice.

I believe you made a good decision in getting the Class D amp, saving money and with the advantage of helping your back with a lighter chassis.

 

[slipperybidness]

How did negative feedback get such a bad reputation?

 

[Verdinut]

I’m just not buying it, Rich. The distortion Putzney is talking about in a Class AB amplifier like the ATI is more than 90db below 1W, but you’re saying the difference is obvious. Either noise is a lot higher, or distortion is a lot higher, or some other effect is involved, like differing levels or a non-flat frequency response. Your results need the proof only measurements can provide.

Of course, Putzney is preaching for his product. There is a very tiny percentage of distortion, so what? Can anyone hear it if it is so low and only measurable with sensitive precision equipment? In my opinion, that's nitpicking and only good for audiophools!

When a Class AB amplifier is adequately biased with the use of diodes, any crossover distortion is eliminated and several Class AB output stages actually operate in Class A for some of the low wattage output while the others always operate in Class AB and also with very low distortion figures, which nobody can hear except the ones with golden ears.

Only a small percentage of audiophiles have been using Class A amplifiers as compared to the Class AB topology. and we know the pros and cons for each one. If the Class AB design hadn't been as good as it is, it would have been abandoned a long time ago.

 

[Verdinut]

I’m just not buying it, Rich. The distortion Putzney is talking about in a Class AB amplifier like the ATI is more than 90db below 1W, but you’re saying the difference is obvious. Either noise is a lot higher, or distortion is a lot higher, or some other effect is involved, like differing levels or a non-flat frequency response. Your results need the proof only measurements can provide.

There could some mismatch between one amplifier and speaker making it sound different from that heard with another amplifier.

As you know, some speakers with impedance curves going very low at low frequencies or weird phase angles will destabilize amplifiers with inadequate power supplies. A high Qts speaker won't have a good transient response when driven by a McIntosh amp with an autoformer in its output stage.

 

[PENG]

How did negative feedback get such a bad reputation?

Power of hearsay.. If you have enough people say it enough times, people (some, or a lot of) will believe it even if it is not factual.

 

[Irvrobinson]

There could some mismatch between one amplifier and speaker making it sound different from that heard with another amplifier.

As you know, some speakers with impedance curves going very low at low frequencies or weird phase angles will destabilize amplifiers with inadequate power supplies. A high Qts speaker won't have a good transient response when driven by a McIntosh amp with an autoformer in its output stage.

Rich and I use the same speakers, and they’re not an especially difficult load, but Salon2s can play quite loud without distortion, and in a large room they can need more than a small amp can provide. But both amps under test are more than powerful enough. I don’t know what Rich was hearing, but to be able to so easily discern a difference between the two says one was probably not functioning correctly. Or they weren’t level matched, but I’ll assume Rich knows how to set up proper comparisons. Since we can’t explain what Rich was hearing, my first conclusion is that measurements are required.

 

[Verdinut]

Rich and I use the same speakers, and they’re not an especially difficult load, but Salon2s can play quite loud without distortion, and in a large room they can need more than a small amp can provide. But both amps under test are more than powerful enough. I don’t know what Rich was hearing, but to be able to so easily discern a difference between the two says one was probably not functioning correctly. Or they weren’t level matched, but I’ll assume Rich knows how to set up proper comparisons. Since we can’t explain what Rich was hearing, my first conclusion is that measurements are required.

Another Factor is that our ears can fool us too. My hearing acuity is far from the one I had when I was 18 when I could hear up to 18 kHz. I'm old enough to remember the annoying 15,734 Hz Flyback transformer sound of early TV sets, which we could definitely hear in the room when the volume was down.

 

[RichB]

Power of hearsay.. If you have enough people say it enough times, people (some, or a lot of) will believe it even if it is not factual.

As I understand the Benchmark position, there are cases, especially at higher frequencies, where phase-shifts interfere with the feedback mechanism. So, feedback is good but, depending on the design, it can become less effective when driving some loads. This can occur at the most sensitive frequencies.
This behavior is not exposed by standard amplifier measurements.

- Rich

 

[Irvrobinson]

As I understand the Benchmark position, there are cases, especially at higher frequencies, where phase-shifts interfere with the feedback mechanism. So, feedback is good but, depending on the design, it can become less effective when driving some loads. This can occur at the most sensitive frequencies.
This behavior is not exposed by standard amplifier measurements.

- Rich

I wonder how phase shifts could interfere with negative feedback? Again, extraordinary claims require some evidence.

 

[PENG]

As I understand the Benchmark position, there are cases, especially at higher frequencies, where phase-shifts interfere with the feedback mechanism. So, feedback is good but, depending on the design, it can become less effective when driving some loads. This can occur at the most sensitive frequencies.
This behavior is not exposed by standard amplifier measurements.

- Rich

Agreed, negative feedback, in fact all feedback, depending on how it's done, could mess things up. My comments was about the sort of generalized statement made on the internet. We can't say no feedback at all is good either, obviously.

 

[PENG]

I wonder how phase shifts could interfere with negative feedback? Again, extraordinary claims require some evidence.

Well, say if you shift it 180 degrees, negative would become positive right? Just teasing..

 

[M Code]

IMHO...
The often mentioned different sounding amplifiers is more dependent upon the loudspeaker. Depending upon the loudspeaker & its X-over design this can/will load an amplifier in a unique way. And when an amplifier is challenged to drive a difficult, reactive load its output transfer function/acoustic signature will likely vary..

Just my $0.02...

 

[RichB]

I wonder how phase shifts could interfere with negative feedback? Again, extraordinary claims require some evidence.

This is not exactly the quote that I was looking for but it does relate to John Siau:

he AHB2 uses feed-forward correction and some feedback. The feed-forward correction is not subject to loop delays and can provide correction at very high frequencies. In contrast, feedback systems have a limited correction bandwidth. If the bandwidth of a feedback system is not adequately limited, the amplifier will go unstable and begin to oscillate. Feed-forward correction is inherently stable.

https://www.audiosciencereview.com/forum/index.php?threads/review-and-measurements-of-benchmark-ahb2-amp.7628/page-7#post-178994

- Rich