Review and Measurements of NAD M27 PWR Amp

[Dan1210]

Hey guys, so I managed to get an M27, I had a Nord before so I have a load of rca to-xlr cables, I’m connecting to a Marantz receiver. If I connect to the Nad with rca to xlr am I losing some gain?

 

[Dan1210]

Just received my Nad M27, all working fine last night but today it seems the 12v trigger has activated a relay and the thing now wont come out of stand by, anyone else had this issue?

 

[Vasr]

Just received my Nad M27, all working fine last night but today it seems the 12v trigger has activated a relay and the thing now wont come out of stand by, anyone else had this issue?

Does the manual standby switch on top work to turn it on and standby? If not, then remove the trigger cable and try the manual switch. Note the instructions in the manual:

The front panel (Standby) button is disabled as long as the male plug of the mono cable (with or without +12V DC) is connected to M27’s +12V TRIGGER IN. Unplug the mono cable for the M27 to be normally switched ON (or back to standby mode) using the front panel (Standby) button.

If it works with manual switch and this is solely related to the use of a trigger from a pre unit, check what cable you are using and the voltage specifications of the two devices for the trigger. These are the most common. Sometimes, when people use a typical audio cable supplied by one or the other device, stereo vs mono or how its is used at either end can make a difference.

 

[Dan1210]

Hey thanks vasr, i have read the manual and tried what you suggested, the unit is ‘bricked’ in stand by mode unfortunately. Gutted as it sounded fabulous last night, will have to go back for repair.

 

[Sal1950]

Hey thanks vasr, i have read the manual and tried what you suggested, the unit is ‘bricked’ in stand by mode unfortunately. Gutted as it sounded fabulous last night, will have to go back for repair.

Unplug the power cord for a few minutes and try again
Good luck

 

[Dj7675]

Anyone know if you could bridge two channels on the M27 Using a modified xlr cable? I know you can do this with regular nc400 amps but wasn’t sure if there was something in the NAD implementation that would prevent this.

 

[Kal Rubinson]

Anyone know if you could bridge two channels on the M27 Using a modified xlr cable? I know you can do this with regular nc400 amps but wasn’t sure if there was something in the NAD implementation that would prevent this.

I did that with the M22, the stereo version of the M27. OTOH, I would check with NAD.

 

[Dj7675]

I did that with the M22, the stereo version of the M27. OTOH, I would check with NAD.

Thanks for that. Will check with NAD. Do you know how many watts in bridged mode the M22 provided? Also, did you make your own xlr cable or did you find it for purchase somewhere?

 

[Kal Rubinson]

Thanks for that. Will check with NAD. Do you know how many watts in bridged mode the M22 provided? Also, did you make your own xlr cable or did you find it for purchase somewhere?

https://www.stereophile.com/content/nad-masters-series-m22-power-amplifier

 

[Dj7675]

https://www.stereophile.com/content/nad-masters-series-m22-power-amplifier

I hadn’t seen that. Thanks for the link. I sent a support request asking if the M27 can be bridged on the M22. Since the cables were sent to you I’m guessing you would have no idea where they got them?

 

[Kal Rubinson]

I hadn’t seen that. Thanks for the link. I sent a support request asking if the M27 can be bridged on the M22. Since the cables were sent to you I’m guessing you would have no idea where they got them?

No but you can buy XLR-splitters easily.

 

[Dj7675]

No but you can buy XLR-splitters easily.

Hi again Kal,
I was looking at your review on the M22. It appears that it was the V1 version of the M22 which does not have the bridge mode like the V2 version does. Now it makes sense why they sent you a cable. I don’t think the cable is a simple XLR Y cable (I could be wrong). With stock Hypex amps (UCD and NCXXX models), from the bit of reading I have done they can be bridged with an XLR Y cable but one side needs the polarity reversed. It seems the M27 shares a lot with the M22 V1 so hopefully it can be bridged with a special cable as well. Will see what NAD says.
I found a used M27 and my rack area is shared by a theater room and my 2 channel room. I am planning on using 3 channels in the theater for LCR and have up to 4 channels to use in my 2 channel room. If I can bridge those 4 channels for my R/L I will, if not, I won’t M27 is a really good value if you can find one used...7 channels of NC400... should be good fun getting it set up.

 

[Kal Rubinson]

I was looking at your review on the M22. It appears that it was the V1 version of the M22 which does not have the bridge mode like the V2 version does. Now it makes sense why they sent you a cable. I don’t think the cable is a simple XLR Y cable (I could be wrong). With stock Hypex amps (UCD and NCXXX models), from the bit of reading I have done they can be bridged with an XLR Y cable but one side needs the polarity reversed. It seems the M27 shares a lot with the M22 V1 so hopefully it can be bridged with a special cable as well. Will see what NAD says.

Yup. I have modified a standard splitter for other reasons. Pretty easy.

 

[Dj7675]

I checked with NAD support, asking them if the M27 could be bridged like the M22 V1 could be bridged. Got a very nice replay back (See below). I have attached the pdf of the cable. With the power supply of the M27 to deliver 7 channels instead of 2, it would be interesting to know how many watts a bridged channel would provide.

Bob Moran (NAD Electronics)
Dec 7, 2020, 3:04 PM EST
Hi Darin,

Thank you for contacting the NAD Support Center about Bridging the M27.

The M27 can be bridged in a similar way to the M22 with a special bridging cable. The cable configuration is detailed in the attached document.

Regarding where to purchase the cable, I suggest contacting Audio Quest to inquire about building you some custom XLR cables in the configuration detailed in the document. Sorry, but NAD does not stock the bridging cable.

I hope this feedback is helpful.

Kind regards,

Bob Moran
NAD Support

 

[Sal1950]

I checked with NAD support, asking them if the M27 could be bridged like the M22 V1 could be bridged. Got a very nice replay back (See below).

Nice of them to provide the info including the pdf of the cable build.. Only forget AudioQuest, contact BlueJeansCable if you'd rather not build it yourself. Good Luck.

 

[Dj7675]

Nice of them to provide the info including the pdf of the cable build.. Only forget AudioQuest, contact BlueJeansCable if you'd rather not build it yourself. Good Luck.

Will see if I think I need it or not (I don’t think I do). But I did already contact bluejeans and they said no problem to modifying an xlr splitter cable. Nice knowing the option is there.

 

[Sined]

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 happy to give the NAD M27 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.

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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/

It's been a while since Amir tested the M27 and these tests of course can't evaluate the long term reliability. I have been enjoying mine for 9 years but over the last two years I had to replace 3 channels that died without any obvious observable signs and no obvious reasons, I never get close to its power limits, listening to music at decent levels.

It is used to feed an active 3 way speaker system, and the two last failures happened on the tweeter circuit. As per SB Acoustics specs, the lowest impedance of the tweeter is 3,2 ohms at approx 3 kHz, I don't think it should be a problem, especially considering that there is really not much power sent in the HF branch (digital XO 1,8 kHz 48 dB/octave). Anyways, this amplifier should be protected against overload or/and over heat. Could it be the protecting 82 uF capacitor that I connected in series with the tweeter that creates a load the M27 doesn't like? I guess if it was the problem, both tweeter channels would have died as long as I turn it on. Anyways, any passive first order passive xover has a series capacitor, so it is not unusual.

Any ASR members here that are long time M27 owners ? Did you have amplifier modules failures?

I can't figure out what's the problem, if you have any an idea of what could be the cause, please let me know.