NAD M23 Stereo Amplifier Review

[ahofer]

It seems like most criticisms of new audio technology are invented by audiophiles out of ignorance to "explain" a subjective (and usually resistant) reaction.

I remember one of my professors at Berklee (back in 1984) "explaining" to me that the "X Factor" of a band happened in between the samples, and that's why digital sounded so sterile. It fits with the adjectives they choose to describe the sounds they imagine with equipment, which often have this owner-and-dog similarity - 'warm' for tubes, "muscular" for big heavy amps, and 'thin' for smaller/lighter equipment.

 

[peng]

No, class A or A/B amps can't reproduce a square wave perfectly either, as perfectly reproducing a square wave requires infinite bandwidth.

You think he knows that? I don"t think so.

 

[anarchist]

I think you need to read more about electronics and Pulse Wide Modulation. A SMPS also uses PWM to provide the current, and digital signals are a form of PWM (PCM form), but in a class D amp it's used to get an analog signal that is a copy of the original signal but way more powerfull. Nowhere there is a digital signal involved.

PWM in class D is not a copy of original analog signal, it's essentially newly generated digital PWM signal (zeros and ones) modulated with source analog signal, the modulated PWM signal is then amplified. The problem is extracting the original analogue signal without distortion is nearly impossible, hence class D remains a niche amplification technology mostly for subwoofer use.
I wonder is Hypex a derivative from hype? I think hype is really the only way to sell this technology to "audiophiles" for multi thousand $.

 

[Mnyb]

No, class A or A/B amps can't reproduce a square wave perfectly either, as perfectly reproducing a square wave requires infinite bandwidth.

Are you here to learn, or are you yet another troll spreading incorrect anti-class D audiophile folklore?

That means nothing reproduce squerewaves properly but that’s ok

Bandwidth limitations shows up the same digital or analog or class whatever does not matter , it’s true that there was fad in hifi with very wide bandwidth amps ( but still not infinite) , maybe it was part and parcel of classic specmanship or to much to late ? very old amps may had to little usable bandwidth ?

Overdoing stuff seems be part of this hobby, it could be that 44.1 KHz for CD is a close shave and demands careful design of filters the solution seems to be 48kHz or maybe 96KHz but now we have DXD at 384kHz ? Just because ? Similar thinking as 500kHz bandwidth amplifiers.

No instruments or singer produce square waves anyway due to that they to have limited bandwidth

 

[Julf]

PWM in class D is not a copy of original analog signal, it's essentially newly generated digital PWM signal (zeros and ones) modulated with source analog signal, the modulated PWM signal is then amplified. The problem is extracting the original analogue signal without distortion is nearly impossible, hence class D remains a niche amplification technology mostly for subwoofer use.
I wonder is Hypex a derivative from hype?

Ok, so you confirmed both that you are ignorant and that you are an anti-class-D troll (maybe because you think it is digital, and are one of those luddites who don't understand digital technology).

An analog signal is also not a perfect reproduction. It is an approximation of the original acoustical signal that is converted into a newly generated voltage, optical signal, or in worst case a mechanical approximation. Extracting the original signal without distortion is impossible.

Just because something is zeros and ones doesn't mean it is digital. You might be confusing it with binary. Digital means representing a signal by regular samples of discrete numerical values - the term "digital" comes from "digits" - numbers, and originally "finger", as in "counting on fingers". The french term for digital, "numerique", describes it even better.

Hypex and purifi use analog PWM. As I explained, they can vary the pulse width continuously, without any discrete steps or quanta.

You also still seem to confuse limited bandwidth with distortion.

 

[pablolie]

PWM in class D is not a copy of original analog signal, it's essentially newly generated digital PWM signal (zeros and ones) modulated with source analog signal, the modulated PWM signal is then amplified. The problem is extracting the original analogue signal without distortion is nearly impossible, hence class D remains a niche amplification technology mostly for subwoofer use.
I wonder is Hypex a derivative from hype? I think hype is really the only way to sell this technology to "audiophiles" for multi thousand $.

So your point is a class A is "better" at maintaining the visual of a *digital signal* (because that's what a square is in most people's mind, even though in practice it never is)?

That is bizarre. Fundamentals aside (nope, no Class A amp nor anything else will ever present a perfect square, it's basic physics), the fact is:

1. Digital signals are very resilient. They do NOT have to be perfect 1 and 0 at all. That is the key advantage of digital - signal integrity is not required to maintain data integrity. A 0.92, a 1.03 etc etc are all perfectly valid 1s. No one cares about a perfect square signal anywhere.

2. Rest assured that when you listen to music there will not be a single square signal anywhere, so it is a silly moot point that doesn't prove anything about the fidelity in the "analog domain" you seem overconcerned about.

Basically, you are using a completely irrelevant proof point to make a weird argument. It's like saying a car is better than another because it drives a bit smoother when you put square-shaped wheels on it... it's like "why on earth would you do that, and wtf do u think it matters?"

Learn a bit about Fourier transformations, which are at the core of Nyquist-Shannon. Hint: it's based on sinus waves, can't get more analog than a sinus wave. One last time: math doesn't lie. Nor does it care about personal interpretations. Sometimes the problem in showing measurements to the uneducated is that they have zero clue how to understand the result. I challenge @anarchist to show us where John Atkinson says anywhere that the square signal result was in any way disappointing, or that he expects a perfect square to pop out on the output side to recommend a product...

 

[antcollinet]

PWM in class D is not a copy of original analog signal, it's essentially newly generated digital PWM signal (zeros and ones) modulated with source analog signal, the modulated PWM signal is then amplified. The problem is extracting the original analogue signal without distortion is nearly impossible, hence class D remains a niche amplification technology mostly for subwoofer use.
I wonder is Hypex a derivative from hype? I think hype is really the only way to sell this technology to "audiophiles" for multi thousand $.

You seem confused.

Just as a continuously varying voltage can encode an analogue signal, so can a continuously varying pulse width. So could also a continuously varying light intensity, or continuously varying current, or continuously varying frequency (that is what FM radio is). Any property you can vary can be used to encode an analogue signal. Hey what about a continuously varying groove depth in vinyl. That's another way.

All are just ways of being an "analogue" of the sound wave (see how that works?) - which is a continuously varying pressure wave. None of them are any more analogue than another.

You really need to learn some stuff about how things work before coming here to troll. You are just showing your ignorance, and are going to get schooled.

 

[Jim Creek]

PWM in class D is not a copy of original analog signal, it's essentially newly generated digital PWM signal (zeros and ones) modulated with source analog signal, the modulated PWM signal is then amplified. The problem is extracting the original analogue signal without distortion is nearly impossible, hence class D remains a niche amplification technology mostly for subwoofer use.
I wonder is Hypex a derivative from hype? I think hype is really the only way to sell this technology to "audiophiles" for multi thousand $.

This post reminds me of the anti-class D propaganda on the SuperBestAudioFriends Web Site.

SBAF is basically a Schiit Audio fan boy site. I have nothing against Shiit Audio since I own a couple of their products. But the regular members at SBAF will attack any post that is positive on Class D or critical of a Schiit product. I know this from experience.

 

[pablolie]

This post reminds me of the anti-class D propaganda on the SuperBestAudioFriends Web Site.

SBAF is basically a Schiit Audio fan boy site. I have nothing against Shiit Audio since I own a couple of their products. But the regular members at SBAF will attack any post that is positive on Class D or critical of a Schiit product. I know this from experience.

At this point it is pretty clear we are being trolled. My suitably-dumbed-down educational goodwill is exhausted. Let this person buy a 200lbs, $40k class A amp and enjoy the superior "sound quality". :-D Square signals and audio performance... what a sad joke if someone really believed it. Try testing speakers with full load like that while you're at it...

 

[HoweSound]

I wonder is Hypex a derivative from hype? I think hype is really the only way to sell this technology to "audiophiles" for multi thousand $.

I have one of the latest generation Hypex amps. I have not heard a better sounding amplifier regardless of class. Obviously you have never listened to a quality class D amp from Hypex or Purifi; or if you have, your biases were fully engaged at the time. Please disparage elsewhere.

 

[Rja4000]

I was just playing with the idea to demonstrate the effect on a square wave of different frequency responses.
So I gave it a try.

Looking at 2 amplifiers:

Benchmark AHB2

Frequency response, from Amir's review

If I see correctly, that's behaving like a 1st order low pass filter at around 200kHz.
Let's say it's a Butterworth 1st order filter.

What would a 10kHz square wave look like ?

Cool.

Now, let's try with the NAD M23, or C298, or whatever amp using the Purifi module.

NAD M23

Frequency response, as per Amir's measurements above

That's a steeper response.
Purifi's datasheet says -3dB at 60kHz and -6dB at 75kHz.

So let's try with a Butterworth 2nd order filter at 60kHz

Square wave at 10kHz would look like

That's different, indeed.
Does it matter ?


Now let's introduce another parameter:
Human hearing

What happens after our ear's own low pass filter is applied ?
That's a very steep low-pass filter, since some may hear at, say, 16kHz, but at 32kHz, for sure, we don't hear anything.
Meaning 0. Nada. -100dB or so at least.

Let's try and apply such a filter on top of the amp filter.

Here is what we'd get as a result.

Benchmark AHB2

NAD M23

In both cases, we get a pure 10kHz sine wave.
Of course, since 3rd harmonic and above are completely inaudible to any human.
(And the theory -and practice- tells us that a square wave may be reproduced by an infinite sum of sine waves at odd multiples of the fundamental frequency, with level decreasing as 1/order)

So are those differences in 10kHz square wave any relevant ?
Not at all.


By the way, don't say a Purifi amp can't do any square wave correctly.

Here is one (predicted) for NAD M23 :

Well, granted, that one is at 1kHz.
So at 60kHz, we already have 30 harmonics (including the fundamental), which allows a pretty accurate reproduction of the square wave.

OK, I had fun

Now let me grab a beer...

 

[antcollinet]

I was just playing with the idea to demonstrate the effect on a square wave of different frequency responses.
So I gave it a try.

Looking at 2 amplifiers:

Benchmark AHB2

Frequency response, from Amir's review

View attachment 306150

If I see correctly, that's behaving like a 1st order low pass filter at around 200kHz.
Let's say it's a Butterworth 1st order filter.

What would a 10kHz square wave look like ?

View attachment 306151

Cool.

Now, let's try with the NAD M23, or C298, or whatever amp using the Purifi module.

NAD M23

Frequency response, as per Amir's measurements above

View attachment 306152

That's a steeper response.
Purifi's datasheet says -3dB at 60kHz and -6dB at 75kHz.

So let's try with a Butterworth 2nd order filter at 60kHz

Square wave at 10kHz would look like

View attachment 306153

That's different, indeed.
Does it matter ?


Now let's introduce another parameter:
Human hearing

What happens after our ear's own low pass filter is applied ?
That's a very steep low-pass filter, since some may hear at, say, 16kHz, but at 32kHz, for sure, we don't hear anything.
Meaning 0. Nada. -100dB or so at least.

Let's try and apply such a filter on top of the amp filter.

Here is what we'd get as a result.

Benchmark AHB2

View attachment 306154

NAD M23

View attachment 306155

In both cases, we get a pure 10kHz sine wave.
Of course, since 3rd harmonic and above are completely inaudible to any human.
(And the theory -and practice- tells us that a square wave may be reproduced by an infinite sum of sine waves at odd multiples of the fundamental frequency, with level decreasing as 1/order)

So are those differences in 10kHz square wave any relevant ?
Not at all.


By the way, don't say a Purif amp can't do any square wave correctly.

Here is one (predicted) for NAD M23 :

View attachment 306156

Well, granted, that one is at 1kHz.
So at 60kHz, we already have 30 harmonics (including the fundamental), which allows a pretty accurate reproduction of the square wave.

OK, I had fun

Now let me grab a beer...

Nice work - bookmarked.

 

[Rja4000]

Nice work - bookmarked.

Thanks
My pleasure

 

[Jukka]

So you saying the distorted output signal in the stereophile review is just our imagination?
It's not really about what can you hear at this point, we cannot hear THD below 0.05% levels, and our speakers distort signal to at least 0.5%, yet we say here that SINAD 90 is superior to SINAD 70?
The point here is that top of the line class D amplifiers are not able to amplify square wave without distortion, and A or AB class amps can.

Try playing back a square wave with a class A/B amp from a subwoofer and try to explain why it's "heavily" "distorted" even when using class A.

 

[Galliardist]

I was just playing with the idea to demonstrate the effect on a square wave of different frequency responses.
So I gave it a try.

Looking at 2 amplifiers:

Benchmark AHB2

Frequency response, from Amir's review

View attachment 306150

If I see correctly, that's behaving like a 1st order low pass filter at around 200kHz.
Let's say it's a Butterworth 1st order filter.

What would a 10kHz square wave look like ?

View attachment 306151

Cool.

Now, let's try with the NAD M23, or C298, or whatever amp using the Purifi module.

NAD M23

Frequency response, as per Amir's measurements above

View attachment 306152

That's a steeper response.
Purifi's datasheet says -3dB at 60kHz and -6dB at 75kHz.

So let's try with a Butterworth 2nd order filter at 60kHz

Square wave at 10kHz would look like

View attachment 306153

That's different, indeed.
Does it matter ?


Now let's introduce another parameter:
Human hearing

What happens after our ear's own low pass filter is applied ?
That's a very steep low-pass filter, since some may hear at, say, 16kHz, but at 32kHz, for sure, we don't hear anything.
Meaning 0. Nada. -100dB or so at least.

Let's try and apply such a filter on top of the amp filter.

Here is what we'd get as a result.

Benchmark AHB2

View attachment 306154

NAD M23

View attachment 306155

In both cases, we get a pure 10kHz sine wave.
Of course, since 3rd harmonic and above are completely inaudible to any human.
(And the theory -and practice- tells us that a square wave may be reproduced by an infinite sum of sine waves at odd multiples of the fundamental frequency, with level decreasing as 1/order)

So are those differences in 10kHz square wave any relevant ?
Not at all.


By the way, don't say a Purifi amp can't do any square wave correctly.

Here is one (predicted) for NAD M23 :

View attachment 306156

Well, granted, that one is at 1kHz.
So at 60kHz, we already have 30 harmonics (including the fundamental), which allows a pretty accurate reproduction of the square wave.

OK, I had fun

Now let me grab a beer...

Interesting, I see that our friend @anarchist owns a Yamaha RX-3080 which is reviewed here: it appears to have bandwidth closer to the M23 than the Benchmark, so presumably would produce a square wave that is also closer to the M23?

Yamaha RX-A3080 Review (AVR)

This is a review and measurements of the Yamaha RX-A3080 Audio/Video Receiver. It was kindly purchased by a member as a refurbished unit and sent to me. This is last year's model and motivation for testing was that it shares the same amplification as this year's models which have very...

audiosciencereview.com

This is about the available harmonics, not the class of amp so much.

 

[SiamXIII]

Will there be any audible upgrade over Topping LA90 for Kef R3s in 3x5m room?

 

[ahofer]

Will there be any audible upgrade over Topping LA90 for Kef R3s in 3x5m room?

At 86db, the KEFs aren’t too efficient. Having the extra power might make a difference, depending on what you listen to and what levels. Borrow a Purifi amp and try (maybe there is an ASR member nearby who would be willing to help - I could, if you were on the UWS of Manhattan).

 

[Julf]

At 86db, the KEFs aren’t too efficient. Having the extra power might make a difference, depending on what you listen to and what levels. Borrow a Purifi amp and try (maybe there is an ASR member nearby who would be willing to help - I could, if you were on the UWS of Manhattan).

But remember that doubling the power only gives you 3 dB more sound pressure.

 

[Holdt]

But remember that doubling the power only gives you 3 dB more sound pressure.

But the Topping LA90 = 56 W @ 4 ohm and NAD M23 = 361 W @ 4 ohm. That's 6x the power.

Poor Kefs will let the smoke out before taking anything near 361 W.

 

[SiamXIII]

At 86db, the KEFs aren’t too efficient. Having the extra power might make a difference, depending on what you listen to and what levels. Borrow a Purifi amp and try (maybe there is an ASR member nearby who would be willing to help - I could, if you were on the UWS of Manhattan).

I have no changes to get my hands on Purify amp in my country. So I guess I would blindly buy M23. At least I will be future-proofed in amp section.