NAD M23 Stereo Amplifier Review

[Snoopy]

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You got to consider realistically and we have an entire thread on this on these forums. This amp costs a 1000-1200 to produce. Manufacturer needs profit, retailer needs profit, and these are where these skips occur. Just imagine on a 500 dollar node lol

Probably a lot of nodes are sold . No surprise that there are reports of failing units.
Its the same with Topping and SMSL.

The question is do you spend 4000 bucks on something made in Japan, the US or Germany that probably will not fail for years and will still be serviced because the manufacturer is still around or do you spend 500 dollar on something from a Chinese brands (and this is not a insult, racist or low quality talk) that might maybe fail after a few years and buy a new unit.

But more and more manufacturers are stuffing more things into smaller boxes with big LCD and oled screens .. I'm not surprised these units die more often.

Look at a NAD M10 or a Cambridge Evo.

 

[MacCali]

Probably a lot of nodes are sold . No surprise that there are reports of failing units.
Its the same with Topping and SMSL.

The question is do you spend 4000 bucks on something made in Japan, the US or Germany that probably will not fail for years and will still be serviced because the manufacturer is still around or do you spend 500 dollar on something from a Chinese brands (and this is not a insult, racist or low quality talk) that might maybe fail after a few years and buy a new unit.

But more and more manufacturers are stuffing more things into smaller boxes with big LCD and oled screens .. I'm not surprised these units die more often.

Look at a NAD M10 or a Cambridge Evo.

I think the problem we face is where it is designed and who builds it. I don’t find any racist issue in your reply. However we know there are definitely quality products which come from every country.

Hell most of everything we own comes out of china. But it depends how you focus your manufacturing. We would assume, fingers crossed, that two different pay grade people are assembling certain things. I would hope someone who does the node won’t touch the master series.

At the same time we could be jumping the gun altogether. It may have been done primarily by machine. Run by a knuckle head.

I mean the only other thing that gets you what you say is in the super high end tier and even though we are not against it. We want to see objective value as well. So for the most part here people outweigh performance to everything else. I find that fair and I am on the same boat. I can definitely dish out a lot of money on crazy things but personally I think that’s nuts and already feel I am way to deep in this.

And as I stated previously no matter how much I enjoyed the Bel Canto black I would never buy that even if it was flawless in measurements.

Regardless with so much audio brands and equipment out there you would drive yourself mad having to think about this. At least with a big brand like NAD you have some piece of mind. Not saying other companies fall through, just that you got nothing to worry about in the mean time. To where a new or up and coming company might make you think and stop you from purchasing.

 

[anarchist]

NAD C298, Stereophiles measurement:

NAD C 298 power amplifier Measurements

Sidebar 4: Measurements

www.stereophile.com

I have two pieces of these, and they function great.

This is especially interesting feature of NAD C 298, square wave sent into the amplifier comes out not exactly square, despite nearly perfect SINAD. I wonder is this a problem with most class D amps?

 

[Rja4000]

This is especially interesting feature of NAD C 298, square wave sent into the amplifier comes out not exactly square, despite nearly perfect SINAD. I wonder is this a problem with most class D amps?

Or, maybe, you see this because you have to measure a class D amplifier with a low-pass filter on the Audio Precision ?
This limits bandwidth, per definition.
And since this measurement is about a 10kHz square wave, you see it.

The NAD C298 anyway has an integrated low-pass filter.

Here is what JA said about it:

"The small-signal bandwidth was restricted by the low-pass filter between the amplifier's class-D stage and its output terminals. Into 8 ohms (fig.1, blue trace), the ultrasonic rolloff reached –3dB at 66kHz. This rolloff lengthened the risetimes of a 10kHz squarewave (fig.2). There is a critically damped overshoot on the tops and bottoms of the waveform, but there is no ringing."

Limiting a square wave to a few harmonics will impact its form.

Here is what looks like a square wave when limited to H5:

Good news: we can't hear it.

 

[antcollinet]

This is especially interesting feature of NAD C 298, square wave sent into the amplifier comes out not exactly square, despite nearly perfect SINAD. I wonder is this a problem with most class D amps?

Nothing to do with Sinad and everything to do with bandwidth as pointed out by @rga4000.

 

[anarchist]

Or, maybe, you see this because you have to measure a class D amplifier with a low-pass filter on the Audio Precision ?
This limits bandwidth, per definition.
And since this measurement is about a 10kHz square wave, you see it.

The NAD C298 anyway has an integrated low-pass filter.

Here is what JA said about it:

"The small-signal bandwidth was restricted by the low-pass filter between the amplifier's class-D stage and its output terminals. Into 8 ohms (fig.1, blue trace), the ultrasonic rolloff reached –3dB at 66kHz. This rolloff lengthened the risetimes of a 10kHz squarewave (fig.2). There is a critically damped overshoot on the tops and bottoms of the waveform, but there is no ringing."

Limiting a square wave to a few harmonics will impact its form.

Here is what looks like a square wave when limited to H5:
View attachment 305883

Good news: we can't hear it.

I'm not convinced we cannot hear it. yes, low pass filter is there as in any class D by design, so what? Class AB amplifiers never show you such distorted signal, because they are true analogue, rather than digitalizing.
NAD C298 uses Purify module BTW, which is not much different to Hypex.

 

[Julf]

I'm not convinced we cannot hear it. yes, low pass filter is there as in any class D by design, so what? Class AB amplifiers never show you such distorted signal, because they are true analogue, rather than digitalizing.
NAD C298 uses Purify module BTW, which is not much different to Hypex.

It has nothing to do with analog ("pure" or not). The signal is not "distorted", and it would look exactly the same if you measured a class A/B amp with a low pass filter. Oh, and by the way, the hypex and purifi class D amps are analog too, no digitizing going on.

What makes you think you can hear it?

 

[anarchist]

It has nothing to do with analog ("pure" or not). The signal is not "distorted", and it would look exactly the same if you measured a class A/B amp with a low pass filter. Oh, and by the way, the hypex and purifi class D amps are analog too, no digitizing going on.

Isn't class D by design converts original signal to PWM, and then back? That's not digitization? I think it is.
The low pass filter supposed to convert PWM back to original signal, but at least in case of Purify it fails to restore original signal fully without distortion.
I now understand better why class D is mostly used for LF amplification, like subwoofers, this type of distortion is not as pronounced in LF band.

 

[Julf]

Isn't class D by design converts original signal to PWM, and then back?

Yes. Analog PWM.

That's not digitization? I think it is.

Digitization means converting the signal into discrete numerical values at regular sample intervals. The purifi and hypex class D amps don't do that, they produce a continuously variable (analog) PWM signal.

The low pass filter supposed to convert PWM back to original signal, but at least in case of Purify it fails to restore original signal fully without distortion.

Bandwidth limiting (that *all* amplifiers do) is not distortion.

I now understand better why class D is mostly used for LF amplification, like subwoofers, this type of distortion is not as pronounced in LF band.

I understand that is your bias that seems to stem from misinformation.

 

[peng]

I'm not convinced we cannot hear it. yes, low pass filter is there as in any class D by design, so what? Class AB amplifiers never show you such distorted signal, because they are true analogue, rather than digitalizing.
NAD C298 uses Purify module BTW, which is not much different to Hypex.

You can easily find out what is the highest frequency you can hear, so no one needs to convince you.

There are many such tests available on the internet such as the one below:

How high can you actually hear? Test yourself and find out

This hearing test will reveal the highest frequency you can pick up...

www.classicfm.com

I am convinced I can barely hear 15,000 Hz, so the output filters of class D amps has no audible effects on me, ymmv.. It is highly doubtful people older than even 20 years old can be bothered by even 25,000 Hz, not with the typical 20-30 dB ambient noise in most living rooms anyway.

 

[anarchist]

Yes. Analog PWM.

Digitization means converting the signal into discrete numerical values at regular sample intervals. The purifi and hypex class D amps don't do that, they produce a continuously variable (analog) PWM signal.

"Pulse Width Modulation (PWM) is a fancy term for describing a type of digital signal"

https://learn.sparkfun.com/tutorials/pulse-width-modulation/all

 

[anarchist]

You can easy find out what is the highest frequency you can hear, so no one needs to convince you.

There are many such tests available on the internet such as the one below:

How high can you actually hear? Test yourself and find out

This hearing test will reveal the highest frequency you can pick up...

www.classicfm.com

I am convinced I can barely hear 15,000 Hz, so the output filters of class D amps has no audible effects on me, ymmv.. It is highly doubtful people older than even 20 years old can be bothered by even 25,000 Hz, not with the typical 20-30 dB ambient noise in most living rooms anyway.

I see, so class D is only good for older people, like retirees...

 

[pablolie]

"Pulse Width Modulation (PWM) is a fancy term for describing a type of digital signal"

https://learn.sparkfun.com/tutorials/pulse-width-modulation/all

Nyquist-Shannon theorem. It results in a perfect analog signal. Math doesn't lie. If you can hear it, you weren't born on planet earth. :-D Many get confused because, to explain PWM visually, they show crude steps to easily visualize things. But when you apply Nyquist-Shannon, the signal will look absolutely and completely analog.

An equivalent is the number Pi. Is it wrong to use 3.14159 in practical terms? Do you prefer to go 3.1415926535897932384626433.... and spend the rest of your life writing it down? Do you think every groove in a vinyl is *perfectly round*?

 

[Waxx]

"Pulse Width Modulation (PWM) is a fancy term for describing a type of digital signal"

https://learn.sparkfun.com/tutorials/pulse-width-modulation/all

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. Digital amplifiers do exist, but they work with pcm input in the amp module and do the conversion at the exit of the amp. A class D is full analog and works only with an analog input (AC signal).

And a pwm is done at 250kHz at minimum and with most modern amps go more like 1 to 1.5MHz. No way you can hear that switching. With older with bad filtering you could, but then we are talking about designs of 20-30 years ago or even longer.

The real problem class D had in the past, was disharmonic noise. You can hear that untill about 100dB (in worst case) noisefloor and it's very annoying (the cold hard sound). Class A or tube amps have a much higher noisefloor, but it's mainly harmonic distortion and that is why many are not bothered at all, they like it as the wamrth of the device.

Modern class D amps often have a sinad above 100dB so even very critical people like me are not hearing it anymore. And to be honest, most people won't hear it at 80dB sinad neighter. Most pro audio power amps aim at 80dB Sinad as good enough. And i've never seen a pro amp going above 100dB sinad. And on high power like in a concert hall or club or festival you won't hear it, the enviroment is to noisy anyway so it's masked.

 

[peng]

I see, so class D is only good for older people, like retirees...

No one said such a thing, where did you read that class d is only for old people? I did mention people older than 20 years old, are those people (such as 21, 22, 30) old by your standard? This is too funny..

 

[anarchist]

Nyquist-Shannon theorem. It results in a perfect analog signal. Math doesn't lie. If you can hear it, you weren't born on planet earth. :-D Many get confused because, to explain PWM visually, they show crude steps to easily visualize things. But when you apply Nyquist-Shannon, the signal will look absolutely and completely analog.

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.

 

[pablolie]

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.

You listen to square waves too much...

 

[Rja4000]

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.

The point here, exactly, is that the amplifier you're referring to limits bandwidth as from 66kHz or so.

Is that a real life concern, of any sort ?
No, it's not.
It never was and will never be for a human being.
Whatever his or her age.

<EOT>

 

[Julf]

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.

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?

 

[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.