NAD M28 Seven Channel Power Amplifier Review

[carlob]

I agree with this, so from what we have here, which one perform better between the all Hypex NC400 DIY kit, and the all Purifi et400a dev Platform?

You can read it yourself, I already posted the links:

Purifi reference build: https://www.audiosciencereview.com/...easurements-of-purifi-1et400a-amplifier.7984/

NC400 DIY build: https://www.audiosciencereview.com/...and-measurements-of-hypex-nc400-diy-amp.5907/

I would say that the Purifi performs marginally better.

 

[carlob]

btw you can buy a NC400 kit directly from Hypex at €575+VAT per channel (everything is included, even the case)
https://www.diyclassd.com/product/nc400-mono-kit-(complete-kit)/24

 

[PeteL]

btw you can buy a NC400 kit directly from Hypex at €575+VAT per channel (everything is included, even the case)
https://www.diyclassd.com/product/nc400-mono-kit-(complete-kit)/24

Thanks, I already have a pair of nc500 Monoblock that I built. The NC 500 I got it with a commercial account, but anybody can also buy the Purifi dev kit, it's about 800 usd, but you need to add the power supply (about 200$), power switch and chassis, but it includes the buffer and the connectors, so also an easy built

 

[amirm]

Here is the teardown: https://www.audiosciencereview.com/...28-7-channel-purifi-amplifier-teardown.15981/

 

[amirm]

Someone asked for multitone test. I added it to the review. Here it is also:

 

[Michael YYZ]

I‘ve got my M28 from amongst the first batch which arrived in Canada on 14 August. When I decided to buy the M17 V2i combo in June/July I was told that the M27 had been discontinued. My dealer sold the last M27 in May.

Once I received it, I opened up the top cover and took photos. I also have the Service Manual for the M27 with which I compared what I saw in the M28. Here are some brief observations:

• Basically, the M28 looks very much alike like the M27 inside;
• The power supply for the M28 is built on a single PCB (unlike the M27 which was on multiple PCBs);
• The MOSFETs in the ouput stage of the SMPS are on their own common heat sink. In the M27 they were on a heat sink parallel to the MCU board;
• The +/- 65 V SMPS output is connected to the MCU board by screwed connectors, instead of plug-in connectors as was the case for the M27. The rail voltage measured +/- 69.4 V with all seven amps idling (no signal; no speakers connected);
• All PCBs are blue (typical for NAD) but the Purifi modules have green PCBs;
• Three Purifi modules have a date code of 19 38 and three have a date code of 20 01. The seventh module is partly hidden by the case;
• Most electrolytic capacitors on the amplifier modules are made by Samwha (on the buffer board; not sure on the Purifi modules);
• The larger capacitors in the SMPS are made by Lelon in the primary stage and Jianghai in the secondary stage;
• The Purifi modules look very much alike to what I’ve seen in various sources online, so I’m guessing NAD purchases them directly from Purifi.

In my opinion, the amplifier sounds very, very nice. It’s been working 24/7 (non-stop) since I received it - at low levels overnight - with no issues.

I don't know until I open it.

 

[Michael YYZ]

@amirm Would it be possible to post the broadband spectrum of a 1 kHz tone? I’d be interested to see the attenuation of the switching frequency. Thanks.

 

[amirm]

I post it in the Purifi review. I doubt it is changed.

 

[Bsinger]

"clear my hurdle of 96 dB for 16 bit content"

Tell me more. Did Amir write something on this or does anyone have recommended reading material? Something that helps put the measurements in context.

 

[Vincentponcet]

Or you combine a 3 channel Purifi with OPA1612 + 4 channel NC502MP for 1600 + 1150 GBP excl VAT respectively.
That translates into 3520 USD excluding taxes and you actually get reference purifi performance and not this NAD "good enough" level (Nord Purifi is already tested on ASR).

Where do you get 3 channels purifi ?

 

[carlob]

Where do you get 3 channels purifi ?

https://www.nordacoustics.co.uk/product-page/nord-three-1et400a-4-channel-amplifier
I am sure there are others

 

[Vincentponcet]

https://www.nordacoustics.co.uk/product-page/nord-three-1et400a-4-channel-amplifier
I am sure there are others

Thanks.
Do you know if we can see inside / teardown?


I'm so sad m28 is such a failure ( loosing 15db of distortion + 6db SINAD + even worse at high power + too much gain, ie have to reduce gain in the source/preamp, ie even higher noise + bad quality caps). I was ready to purchase it without having read a review. Thank you very much for your hard work @amirm !

 

[carlob]

Do you know if we can see inside / teardown?

You can ask @boggit10

 

[spaceboi]

Hi All,

i've been lurking around here for while and finally decided to register.

I just received my M28 last week and love it... and i also have a M27 (18 months old).. and i "personally" prefer the sound of the M28 in my system,
As i'm running a 13channel system the plan was to get 2 M27's and then i opted for the M28 for the main channels.

I've been A/B'ing these amps all week and there are many tonal similarities in sound, but i'm finding something extra in what the M28 does for my tastes.

For context, i am running a Marantz AV8805 using XLRs into the NADs and they are driving 3 x Bowers HTM2 D3s (as matching LCRs)

My testing is using mostly music from either CD or Tidal (via Heos).

So before anything, i just wanted to listen to each amp on it's own merits and not based on technical read-outs (i got this amp a few days prior to Amir's M28 report).

Straight away i noticed a change in vocals with a little more forwardness (NOT brightness), but also a slightly more articulate presentation of the spoken words... it was only subtle, but it was there.. the soundstage also seemed a tad wider and deeper and it seemed a little more stable overall.

after playing with the music, i setup my PC with REW and UMIK1 mic and ran the basic sweep tests (that's as technical as i can go)

Below is my centre channel via the M28 (blue) and the M27 (red) run as LARGE (just for this test) and with absolutely no EQ, etc

What this chart isn't showing is that the M28 was 0.5dB louder across the range, so i've dropped it 1/2 dB to match and show any real variances.
I've also applied 1/3 smoothing.

FYI i ran these sweeps several times each and the variance you see from 5kHz and up was essentially the same each time. (and this also occurred with the Front Left and Right channels as well).

Perhaps that slight increase from 4-5Khz range is what i noticed with my above comments.

In a nutshell they are both killer amplifiers, but i personally prefer the sound of the M28, so with Amir's specs being so similar to his M27 specs, it may just come down to personal taste.

 

[Apollon Audio]

I bet that @Apollon Audio and @boggit10 (Nord) could make a 7 channel custom amp if asked. We would have to quote them, but I expect the price to be similar.

Actually our 4,5,6,7 and 8 channel Purifi miltichannel based amps are coming out next month. Enclosures are our new premium in house made enclosures just like our PNC1200 and 1ET400A mini.

Our upcoming multichannel Purifi based amps have all power available from each 1ET400A module per channel even when all channels are driven and the harmonic distortion stays low @ 0.0006% THD+N for all channels.

The price will be around 4.490 Euro excl. VAT for the 8-channel version and less for other versions.

 

[Vasr]

@spaceboi Your perception of the differences can be entirely due to the 0.5db volume difference between the two or it could be expectation bias from having acquired a newer toy. Hard to say without doing a double blind test. In theory, you shouldn't be able to hear any difference between the two at this level of performance.

REW measurements (which are dominated by room modes) are not very reliable indicators of amp performance. Any amp/speaker combination will have some variances even if you manage to place the measurement mic at the exact same position for both. But those differences at those frequencies are very position dependent and so may not correlate in any way at your listening position. Also, it is not clear from your writing whether you just dropped the graph by 0.5db in REW or adjusted the gain between the two amps themselves to match the outputs. If the former, then that could also explain the variances depending on your room modes.

Gross differences like significant roll-offs at either end can affect the tonal balance. Not these kinds of differences within measurement error range.

 

[spaceboi]

@spaceboi Your perception of the differences can be entirely due to the 0.5db volume difference between the two or it could be expectation bias from having acquired a newer toy. Hard to say without doing a double blind test. In theory, you shouldn't be able to hear any difference between the two at this level of performance.

REW measurements (which are dominated by room modes) are not very reliable indicators of amp performance. Any amp/speaker combination will have some variances even if you manage to place the measurement mic at the exact same position for both. But those differences at those frequencies are very position dependent and so may not correlate in any way at your listening position. Also, it is not clear from your writing whether you just dropped the graph by 0.5db in REW or adjusted the gain between the two amps themselves to match the outputs. If the former, then that could also explain the variances depending on your room modes.

Gross differences like significant roll-offs at either end can affect the tonal balance. Not these kinds of differences within measurement error range.

Sorry, should have clarified - once I ran REW and noticed the variance i manually change the output to match for listening. and honestly did not notice the volume change, or at least didn't notice any change in the overall sound performance.

These are both awesome amps and have similar overall tones/richness, but the vocals for me stood out as more natural, more than the rest of it, and as subtle as is it, i liked what i heard.

Oh, and to certify this claim 100%, with results even Amirm can not dispute- i had my "i-do-not-know-why-you-need-to-keep-buying-new-things-but-notices-every-difference-without-being-aware-of-what-has-changed-in-the-system" partner blind test the setup for me, saying nothing about what was what playing and every time i played the M28 the response was a simple "i like that one it just sounds a bit nicer".)

so, who am I to argue with that

 

[Michael YYZ]

Thanks very much, Amir. I look forward to it.

I post it in the Purifi review. I doubt it is changed.

 

[amirm]

The price will be around 2.990 Euro excl. VAT for the 8-channel version and less for other versions.

You should send a multi-channel one in for review. Since I started to test AV products, we have a lot of home theater enthusiasts here wanting multichannel amplification.

 

[Vasr]

Sorry, should have clarified - once I ran REW and noticed the variance i manually change the output to match for listening. and honestly did not notice the volume change, or at least didn't notice any change in the overall sound performance.

These are both awesome amps and have similar overall tones/richness, but the vocals for me stood out as more natural, more than the rest of it, and as subtle as is it, i liked what i heard.

Oh, and to certify this claim 100%, with results even Amirm can not dispute- i had my "i-do-not-know-why-you-need-to-keep-buying-new-things-but-notices-every-difference-without-being-aware-of-what-has-changed-in-the-system" partner blind test the setup for me, saying nothing about what was what playing and every time i played the M28 the response was a simple "i like that one it just sounds a bit nicer".)

so, who am I to argue with that

If you are happy with that subjective evaluation, great for you while it may not apply to anybody else. But you have indeed gone against one of the fundamental premises of the site that all audible artifacts are measurable and manifest themselves in the amp measurements. It is certainly not the REW measurements you did that satisfies that.

But you have the endorsement of a higher authority than Amir, so who can argue.

In any case, people can wax poetic about the audible quality of decent measuring equipment (perhaps even more so if the latest Class D) without getting harassed here. Just be glad you didn't do this for a Class AB with a 96db SINAD. You would have been roasted from here to hell.