Review and Measurements of NAD M27 PWR Amp

[Matias]

One thing the NAD has which Hypex modules in a box from small outfits don't have is enough gain to work with the typical unbalanced DAC.

With Apollon you can order with the gain and input impedance you wish. I chose mine to the standard values.

 

[Ron Texas]

With Apollon you can order with the gain and input impedance you wish. I chose mine to the standard values.

I will have to check that.

 

[Sal1950]

Sal, an Emotiva XPA Gen 3 could be arranged


I wonder how using the M27 to bi-amp all three front Left, Center, and Right speakers with the 7th amp unused would affect everything you mentioned...

That would be kool, talk to Amir. He be's the bossman.

 

[AndrewDavis]

And here I thought we were all going to have to buy four Benchmark AHB2s to get a good 7.1 experience.

 

[amirm]

Here is the teardown: https://www.audiosciencereview.com/.../teardown-of-nad-m27-surround-amplifier.9040/

 

[maty]

Maybe the 5 db of SINAD difference is thanks the extra capacitors bank of the modules Hypex NC400 OEM v0.1

We need measurements of a NC500 without the eval board, with a modern boutique buffer.

 

[maty]

Mattias, I tell you a secret. If the PURIFI was built, I planned to add a capacitor bank to the Cresnet SMPS, up to 8,000 uF. Of course, after having done the necessary burning, as many say that the class D need many hours of operation, hundreds, to stabilize the sound.

https://www.diyaudio.com/forums/vendor-s-bazaar/281413-audio-smps-units-sale.html

Mundorf M-lytic 47,000 uF needed at least two hundred hours. The sound was changing ostensibly, at least I appreciated it many times in my first system, the kidnapped by the TV and ... I am surprised that the same thing happens in electrolytics of much less capacity. And yes, appreciated even with the sound of the TV, from an AVR Yamaha RX-V2700 (now I have other AVR more modern).

https://www.audiosciencereview.com/...own-of-iom-ncore-pro-pwr-amp.9004/post-229508

 

[peng]

This is a review and detailed measurements of the NAD M27 7-channel surround audio amplifier. It is on kind loan from a member. Seems like the M27 came out back in 2014 and costs US $4,400.

The M27 has the same design language as the excellent M17 Home Theater Processor (looks only):

View attachment 33628​

The enclosure, especially the top surfaces, oozes quality and luxury in the way that many high-end audio companies fail at. And the looks are actually functional with ample ventilation holes for proper cooling. I will do a teardown later to show this in more detail.

One strange bit of functionality is that the NAD logo lights up orange but goes off when the amplifier is turned on using the touch button on top. This is backwards but fits the functionality for home theater use in darkened room.

The rear panel takes the high quality look of the front and top to the back:

View attachment 33629​

Everything from XLR connectors to speaker terminals is stout and feels solid.

In use, the amplifier when driven in two channel mode, never came remotely close to complaining, shutting down, etc. which I frequently see in AVRs.

Heat dissipation at first is very modest but after half hour of use, the idle power consumption of the rest of the unused channels served to warm up the top. No worries though as it was not remotely "hot." This is due to use of switching power supply (single one powering all the channels) and class D amplifiers based on design from Hypex nCore series. The actual implementation is custom which I will show in teardown.

For my testing, I focused on XLR input only. I hope if you buy an amplifier of this class, that is the connection you use.

Power Amplifier Audio Measurements
As usual, we start with our dashboard, driving two channels into 4 ohm at 5 watts:
View attachment 33630

Ah, what a relief it is to see excellent SINAD (signal over noise and distortion) in home theater space after testing so many subpar amplifiers in AVRs. Distortion products are around -110 dB. Ironically, this is far better than the processor and AVR DACs we have tested. In 2-channel world, our desktop class are usually way ahead of amplifiers but not in home theater. So far anyway.

The very nice showing in noise and distortion puts the M27 amplifier near top of the class:
View attachment 33631

Spectrum of 1 kHz FFT shows the typical switching frequency in 400+ kHz:

View attachment 33632

Here is the frequency response:

View attachment 33645

There is a kink in there around 50 kHz but seeing how it is way out there as far as audiblity, it should be OK. May differ though with a real speaker load.

Crosstalk is very good:
View attachment 33634

Dynamic range at around rated power is excellent (better than 20 bits in digital terms):

View attachment 33635

Even at rated power you have 105 dB or 17.5 bits.

Most important test is THD+N (distortion+noise) relative to power level as we increase input. Here it is at 4 ohm:

View attachment 33646

Wow, this is one powerful beast in stereo mode. Courtesy of a power supply that is designed to feed 7 channels, it is not a bottleneck in 2-channel mode allowing these class d modules to sing. And sing loud!

8 Ohm output is also quite good:

View attachment 33637

Of course in neither case we are able to match the state-of-the-art 2-channel amplifiers from likes of Benchmark or Purifi. But what is there at -90 dB or better should be quite excellent.

Peak power as you can imagine, is even higher:
View attachment 33638

Here is a refined version of a recent test: I sweep for power using different frequencies from 20 kHz on down to just 20 Hz. Test bandwidth is 45 kHz so that it allows enough harmonics to be included in the test but not too much that it just shows ultrasonic noise-shaping and such:

View attachment 33647

As expected, at low frequencies we have lowest distortion (lowest graphs) but we clip due to much larger power demand of these "slow" waves.

Conclusions
The NAD M27 surround power amplifier has exceptional looks and build quality. It is beautiful to look at. That beauty runs way deep into its veins, producing lots of power in a class-leading way. Efficiency of class-d power amplifier and switching power supplies serve to keep the unit quite cool for its power rating and number of channels. Great attention has gone into heat management and signal flow -- something I don't normally see in DIY hypex ncore builds.

Yes, at US $4,400 it is not cheap but you are getting 7 channels of amplifications. That is roughly $630/channel which is actually quite competitive.

I am probably drunk but from good measurements and great looks of NAD M27 but I am happy to give it one of my highest recommendations.

If you have a home theater and want a gorgeous, powerful and performant multi-channel amplifier, your search is over. Get the M27 and worry about money for food later.

------------
As always, questions, comments, recommendations, etc. are welcome.

It has been raining and raining hard. Starting to get to me. I need to go to a steak and lobster dinner to drown out m sorrows. As usual, my appetite is ahead of what money I want to spend so need your donations: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/

Thank you for such a great objective review!! Best I have seen so far.. If done consistently the same or very similar way, it should be easy to compare this amp to the others you are going to be testing..

By the way, sorry if asked and answered before, why would you stick with the term "SINAD", when the way you measure, it should be equal to "THD+N" that is commonly used in other online reviews right? I think when some of us linked your measurements on other popular forums such as AH, the guys there would understand THD+N but not SINAD, and they google it, unless they have a little technical knowledge, they could get confused and wouldn't know how to compare with other measurements they read from AH, S&V, Stereophile etc. On the other hand, you do always show both side by side, so no one should be complaining, but I am sure some still get confused if they don't know that the two are actually the same.

 

[DonH56]

By the way, sorry if asked and answered before, why would you stick with the term "SINAD", when the way you measure, it should be equal to "THD+N" that is commonly used in other online reviews right? I think when some of us linked your measurements on other popular forums such as AH, the guys there would understand THD+N but not SINAD, and they google it, unless they have a little technical knowledge, they could get confused and wouldn't know how to compare with other measurements they read from AH, S&V, Stereophile etc. On the other hand, you do always show both side by side, so no one should be complaining, but I am sure some still get confused if they don't know that the two are actually the same.

Been discussed. If you go to things like IEEE Standards (1241, 1057, etc.) THD+N is not the same as SINAD. Most reviews do actually report SINAD and call it THD+N. Technically (per IEEE Standards) SINAD is the ratio of signal to all other components; SNR is the ratio of signal to (typ non-correlated) noise without distortion spurs; and, THD+N is the ratio of signal to THD spurs and non-correlated noise. THD+N would leave out say power supply spurs where SINAD includes them. And so forth.

IME/IMO - Don

 

[thomasjast]

Oh my God... thank you! I've owned one of these for a couple of years and I know it's amazing, but was always afraid of the ugly truth that may have been lurking. Woohoo!

Thanks for sending it in for testing! Appreciate it!

 

[laidick]

The direct competitor would be ATI 527/528nc which is using multi NC500 modules in similar price range.
Or the Apollon NCMP8350 with 4 NC502MP modules.

Hope someone could send amir for review.

 

[elberoth]

Amir, can you post intermodulation test with 19 and 20 kHz tones ?

 

[amirm]

Amir, can you post intermodulation test with 19 and 20 kHz tones ?

Sure. At what power level? 5 watt or max?

 

[elberoth]

Sure. At what power level? 5 watt or max?

That is good question. Same as the Purifi one you posted would be best:

https://www.audiosciencereview.com/...ifi-1et400a-amplifier.7984/page-3#post-194442

 

[amirm]

Looks like I have been running 19+20 kHz test at 5 watts so here it is:

Intermodulation distortion in audio band is roughly the same as Benchmark AHB2 and possibly a hair better. That is extremely high praise! The AHB2 though has a lower noise floor though by 8 dB or so. That is hard to do.

The FFT has 32K points by the way so actual noise floor is 42 dB or so higher than what is shown.

 

[amirm]

That is good question. Same as the Purifi one you posted:

https://www.audiosciencereview.com/...ifi-1et400a-amplifier.7984/page-3#post-194442

Our posts crossed. So I ran it against the Purifi too:

Purifi 1ET400A is definitely more linear. It almost has no intermodulation distortion products. And lower noise floor too although not as good as Benchmark AHB2.

 

[amirm]

Did someone ask for the RCA input measurements? If so, here it is:

I can't tell any difference between this and XLR input this morning (there is tiny run to run variation). So you can be comfortable using either input.

 

[GrimSurfer]

Impressive.

 

[peng]

Dynamic range at around rated power is excellent (better than 20 bits in digital terms):
Even at rated power you have 105 dB or 17.5 bits.

Where was the "105 dB shown", from the graph below on the right, shouldn't DR be 124 dB? Isn't DR = SNR when SNR is measured at max power output?

Also, was the SNR measured "A" weighted or "unweighted" and was any AES17 filter used? It says 22.5 kHz BW, so it seems unweighted but if some sort of low pass filter right?


View attachment 33635

 

[amirm]

Where was the "105 dB shown", from the graph below on the right, shouldn't DR be 124 dB? Isn't DR = SNR when SNR is measured at max power output?

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.