Review and Measurements of NAD M27 PWR Amp

[jhaider]

Good to see this amp is a great performer! When my previous 7-channel amp had issues, I debated between NAD M25 and ATI AT4007 as replacements. After consulting with people I trust I ended up going with ATI, but it was a close call.

Unfortunately I don't see you measuring ATIs AT400x or AT600x, simply because they are so much heavier than Class D or Benchmark. I'm certainly not taking mine - shipping weight ~105lbs! - out of the cabinet!

 

[audimus]

Unfortunately I don't see you measuring ATIs AT400x or AT600x, simply because they are so much heavier than Class D or Benchmark. I'm certainly not taking mine - shipping weight ~105lbs! - out of the cabinet!

If Amir could standardize his measurement procedure and franchise it to volunteers around the world to duplicate who may have the resources to do so, then perhaps there will be opportunities to test it within driving distance for most equipment.

One man operation is not very scalable for this purpose.

Or we could wait for the site to get enough visibility for manufacturers to start sending units directly for testing.

Not that I am holding my breath for either.

Another option to consider is to create a network of people in his area who may be well connected enough to get loaner units from local dealers.

 

[digicidal]

If Amir could standardize his measurement procedure and franchise it to volunteers around the world to duplicate who may have the resources to do so, then perhaps there will be opportunities to test it within driving distance for most equipment.

One man operation is not very scalable for this purpose.

Or we could wait for the site to get enough visibility for manufacturers to start sending units directly for testing.

Not that I am holding my breath for either.

Another option to consider is to create a network of people in his area who may be well connected enough to get loaner units from local dealers.

Well, if you send me an AP555x I'll talk to @amirm to make sure I'm doing everything correctly and get started right away.

 

[amirm]

If Amir could standardize his measurement procedure and franchise it to volunteers around the world to duplicate who may have the resources to do so, then perhaps there will be opportunities to test it within driving distance for most equipment.

There is no business model behind what I am doing let alone have others involved at the same level of expenditure, time and resources. That is the bottleneck, not the tests themselves.

 

[amirm]

Or we could wait for the site to get enough visibility for manufacturers to start sending units directly for testing.

Not that I am holding my breath for either.

This is happening gradually and is bound to get better and better over time.

 

[audimus]

There is no business model behind what I am doing let alone have others involved at the same level of expenditure, time and resources. That is the bottleneck, not the tests themselves.

Didn’t mean to imply it was a business. I used franchise in the sense of creating a recipe that others can follow so that the measurements are comparable. It would be other volunteers willing to donate time and resources to set up their own shop. Not sure how much such a setup would cost though. So, may not be practical.

 

[audimus]

This is happening gradually and is bound to get better and better over time.

Problem is it will be self-selective for manufacturers who know they will measure well or small operations that can benefit from visibility. These measurements are not something they have not done themselves or unaware of before sending. So, it will be a skewed sample but something is better than nothing.

Until there is a “Independently tested by ASR” seal that consumers would look for before purchase that requires manufacturers to have to do it for business reasons.

 

[Blumlein 88]

Problem is it will be self-selective for manufacturers who know they will measure well or small operations that can benefit from visibility. These measurements are not something they have not done themselves or unaware of before sending. So, it will be a skewed sample but something is better than nothing.

Until there is a “Independently tested by ASR” seal that consumers would look for before purchase that requires manufacturers to have to do it for business reasons.

Self selection is very good then. Amir will get the best that way without having to test all the worthless stuff out there.

Should this become even somewhat important in the market of some items, I expect some will do their own measurements in dispute, but not offer up samples.

 

[peng]

I am measuring it both at full rated power and 5 watts:

105 was me rounding the amounts on the left. The one on the right is at full power.

But the one on the left is for 5 W so that means "Even at rated power you have 105 dB or 17.5 bits." the 105 was a typo as it should be 124 dB (with rounding) at rated power.

Could you please confirm that those SNR numbers are "unweighted"?

 

[DonH56]

But the one on the left is for 5 W so that means "Even at rated power you have 105 dB or 17.5 bits." the 105 was a typo as it should be 124 dB (with rounding) at rated power.

Could you please confirm that those SNR numbers are "unweighted"?

The SNR on the left plot is listed as "relative to 5 W" so the signal is 5 W and (integrated) noise level ~104 dB below that. SNR can be measured at any power level and is stated relative to the signal level, not some (effectively arbitrary) other value, unless I am missing something? SNR is typically stated relative to full power but that statement needs to be made explicitly to define the signal level. I have some data sheets showing SNR at 1 W and full power, and the SNR is scaled appropriately.

Hopefully unweighted...

 

[audimus]

Self selection is very good then. Amir will get the best that way without having to test all the worthless stuff out there.

There is a logical flaw in the assumption there that results in Amir having to continue to test crap to make it useful in reality. Will leave finding it as an exercise for extra credit. Hint: Not A => Not B does not imply A => B.

 

[GrimSurfer]

The SNR on the left plot is listed as "relative to 5 W" so the signal is 5 W and (integrated) noise level ~104 dB below that. SNR can be measured at any power level and is stated relative to the signal level, not some (effectively arbitrary) other value, unless I am missing something? SNR is typically stated relative to full power but that statement needs to be made explicitly to define the signal level. I have some data sheets showing SNR at 1 W and full power, and the SNR is scaled appropriately.

Hopefully unweighted...

I understand that measuring SNR at full power is standard industry practice. There is, of course, a self-serving reason for this: Full power is typically where noise is at the nadir. That's why the industry has adopted this practice, even though nobody drives their amp at full rated power (unless they're meth heads and are MCing a rave).

For reasons of common useage, I really like @amirm measuring SNR at both rated power and 5W. It allows one to get a sense of where the noise floor is in common useage. It also allows one to interpolate, as the SNR of most amps follow a linear slope between ~1W and full rated power.

And, yes, hopefully unweighted.

 

[peng]

The SNR on the left plot is listed as "relative to 5 W" so the signal is 5 W and (integrated) noise level ~104 dB below that. SNR can be measured at any power level and is stated relative to the signal level, not some (effectively arbitrary) other value, unless I am missing something? SNR is typically stated relative to full power but that statement needs to be made explicitly to define the signal level. I have some data sheets showing SNR at 1 W and full power, and the SNR is scaled appropriately.

Hopefully unweighted...

I realized it could be measured at any level, and therefore the level has to be stated, but that's why I thought Amir had a typo, because the 105 dB he referenced was for 5 W, and 5 W is clearly not "rated output". Anyway, I think I got the answer, thank you. Oh and yes, I hope it was unweighted too, as he it does say 22.5 kHz BW, if that 22.5 kHz is between 20 Hz and 22,480 Hz or something close to that..

 

[DonH56]

I realized it could be measured at any level, and therefore the level has to be stated, but that why I thought Amir had a typo, because the 105 dB he referenced was for 5 W, and 5 W is clearly not "rated output". Anyway, I think I got the answer, thank you. Oh and yes, I hope it was unweighted too, as he it does say 22.5 kHz BW, if that 22.5 kHz is between 20 Hz and 22,480 Hz or something close to that..

Ah, I misunderstood, typo in the text. Yes, sorry about that. I'm only good for looking at pictures lately.

 

[HammerSandwich]

For reasons of common useage, I really like @amirm measuring SNR at both rated power and 5W. It allows one to get a sense of where the noise floor is in common useage.

On the low side, I'd prefer using 0dBW (aka 2.8V), so that it can be compared to speaker sensitivity easily. e.g., "This amp has only 85dB SNR, but it'll be fine on my 82dB speakers but not 104dB JBLs."

That said, I don't believe it's worth changing now that ASR has a record of 5W performance. That's 5W into 4 ohms, so just subtract 4dB to get SNR at 1dBW.

EDIT - 2.8Vrms is 0dBW, not 1. How the heck did you guys let me get away with that?

 

[restorer-john]

I understand that measuring SNR at full power is standard industry practice.

Industry standard S/N ratio was generally rated with respect to 1 Watt@8ohms and full manufacturer's rated power.

Amir has picked 5W for his own reasons, and an arbitrary maximum power. The maximum power number may differ from the manufacturer's rated power too, as it is based on a determination of the 'knee' in the THD curve and is open to interpretation. In other words, the goal posts are continually shifting and correlation between manufacturer's claims and tested outcomes for S/N should be taken with a grain of salt.

 

[digicidal]

Amir has picked 5W for his own reasons, and an arbitrary maximum power. The maximum power number may differ from the manufacturer's rated power too, as it is based on a determination of the 'knee' in the THD curve and is open to interpretation. In other words, the goal posts are continually shifting and correlation between manufacturer's claims and tested outcomes for S/N should be taken with a grain of salt.

Even the rated output selection is somewhat arbitrary between manufacturers it seems. Some pick the lowest distortion point (which puts them in the "modest power rating" camp, of which NAD was one traditionally), others the highest output where THD+N is under .1% or even under 1% on some (which puts them in the "max power rating" camp) and still others seem to just pick a nice round number (i.e. whatever multiple of 25W is closest to max output).

Like everything else in the marketing vs. measurement comparison - without detailed explanations, approximations are all that's possible. In this particular case, NAD provides so little in the way of detailed specifications that it would be quite difficult to have a true apples-to-apples evaluation IMO. I've found that 67.899% of all statistics are actually bullshit... including this one.

 

[restorer-john]

Even the rated output selection is somewhat arbitrary between manufacturers it seems. Some pick the lowest distortion point (which puts them in the "modest power rating" camp, of which NAD was one traditionally), others the highest output where THD+N is under .1% or even under 1% on some (which puts them in the "max power rating" camp) and still others seem to just pick a nice round number (i.e. whatever multiple of 25W is closest to max output).

Yes, agreed, but does it matter? Rated output is just that- rated. If you don't test to that rated figure and report the results, you have no business calling the manufacturer out for failings outside those figures.

If they rate at 0.003% @150W/8ohms and you find the amplifier puts out 200W @1% what have you actually discovered? Nothing really. If the amplifier fails to hit its rated power at the rated THD, then you have something to bleat about.

 

[HammerSandwich]

...arbitrary maximum power. <snip> In other words, the goal posts are continually shifting and correlation between manufacturer's claims and tested outcomes for S/N should be taken with a grain of salt.

True enough, especially the 2nd bit.

For comparing ASR-only results, however, the full-power SNR should be within 1dB. No way he's going to miss the max-power wattage by 50+%, even if it's not always reported at exactly 0.01%.

 

[digicidal]

Yes, agreed, but does it matter? Rated output is just that- rated. If you don't test to that rated figure and report the results, you have no business calling the manufacturer out for failings outside those figures.

If they rate at 0.003% @150W/8ohms and you find the amplifier puts out 200W @1% what have you actually discovered? Nothing really. If the amplifier fails to hit its rated power at the rated THD, then you have something to bleat about.

Agreed. In an optimal world, manufacturers would provide comprehensive specifications and conditions under which they were achieved, and then @amirm could validate them exactly. Unfortunately, this would decrease the number of reviews he could complete - and in general would be meaningless because this very thing would make the specifications trustworthy for the most part - eliminating most of the need for measurements.

However, my point was only that while there might not be a reliable standard of comparison between ASR measurements and manufacturer specifications - there are likewise not many from one manufacturer that can reliably be compared to another either. As long as ASR measurements can be compared to other ASR measurements - we can't necessarily call the manufacturer out for "lying" per se, but we can definitely say "under the same conditions, this device underperforms by X% in Y metric" - which is enough for me at least.