NAD M28 Seven Channel Power Amplifier Review

[TomJ]

Not sure I understand your point...

Agreed as to why people buy amps. Context is our SINAD rankings which are confounded by gain differences, and from an engineering (not consumer) standpoint. All else being equal, SINAD declines with increasing gain, eg see AHB2 SINAD at its three gain settings. - cheers, Tom

 

[AndrewDavis]

So they sacrificed noise and distortion performance for a few more watts of output.. I’d say it wasn’t worth it..

I agree in principle. But when it's sacrificing noise and distortion you won't hear for a few watts you won't use, I'm ambivalent.

 

[Casey Leedom]

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.

By the way, I specifically ask Nord months ago if they’d be willing to do a 7-channel Purifi amplifier and they said no: not enough perceived demand.

Casey

 

[Matias]

By the way, I specifically ask Nord months ago if they’d be willing to do a 7-channel Purifi amplifier and they said no: not enough perceived demand.

Casey

In production sure not, but a custom 1 amp, maybe they would.

 

[PeteL]

In production sure not, but a custom 1 amp, maybe they would.

I don't know about Nord, but even just sticking firmly to reference designs, I don't see how making just one amp can be sold at a competitive price, just figuring out a mechanical assembly that make sense, design the back panel with some sort of labeling, silk screen or laser engraving, the tooling the routing. Then again maybe some people have too much time and accept to work for free. Or maybe if the customer has unlimited budget.

 

[gvl]

All channels driven to max power will surely trip the breaker on a typical household US circuit.

 

[PeteL]

It’s spooky how similar the xlr and rca measurements are.. is it even a real balanced input?

They would have to really try hard to turn a Purifi module based design into an unbalanced design.

 

[Dj7675]

Actually @March Audio volunteered to take a whack at doing a 7-channel Purifi amplifier for me, but it would have been a one-off and I didn't feel that it would have been fair to Alan to put him through that effort since I'm probably one of the few people interested in a high-end 7-channel amplifier ... If I had the space I would have bought 7 of Alan's Purifi mono blocks ...

Thanks for testing it @amirm! I don't suppose anyone from NAD is on Audio Science Review? It would be interesting to get their input on the tradeoffs they made ...

Casey

I tried contacting them multiple times regarding the T758V3. I did get a response... "We do not comment on 3rd party reviews". It is unfortunate and I wish they would reconsider. Even doing something like Denon where they just communicate directly with Amir would be really nice. They make some interesting gear... some with issues, some pretty good performance, some very good. It would be nice to have their input.

 

[restorer-john]

I've been complaining about switch for the last 5 years:

Maybe the top mounted, wierd functioning touch switch is a pet design by an senior sales executive at NAD. Someone who wanted a point of difference instead of actual functionality.

 

[HTNut1975]

So, with the gain setting that this is on, what advantage does the M28 have over the M27 if anything at all? I’ve read comments before by Bruno and perhaps Allen at March stating that that Purifi just sounds better (the Purifi over the hypex) but not sure beyond that (and that may be nullified by the NAD M28 gain setting?).

 

[twofires]

I'm assuming this performance will hold true for the M33 all in one box and the cheaper C298 power amp. Guess that solves my NAD v Benchmark conundrum.

This is the main reason I come here. Not for the Class AB trash talk, but because marketing departments shouldn't claim (or hint at) what they can't deliver.

 

[HTNut1975]

I'm assuming this performance will hold true for the M33 all in one box and the cheaper C298 power amp. Guess that solves my NAD v Benchmark conundrum.

This is the main reason I come here. Not for the Class AB trash talk, but because marketing departments shouldn't claim (or hint at) what they can't deliver.

I wouldn’t make that assumption because there is a feasible explanation for the increase in gain (I.e., multichannel amp is designed for weaker outputting AVR/AVP’s ). I think a comparison to the Benchmark should be a yet to be designed/manufactured NAD “M23” (I just made up that name—I assumed it might be that for an NAD 2 channel purifi replacement for the M22).

 

[Timbo2]

All channels driven to max power will surely trip the breaker on a typical household US circuit.

That's a really interesting observation. Looking at the specs: https://nadelectronics.com/product/m28-seven-channel-power-amplifier/

You get the usual incomplete story - you don't get a rating for all channels at FTC power. So playing games you can see at 100% efficiency it needing something like 20A. It's obviously going to need more, but your breaker won't trip until it heats up as well.

So here in the land of 120VAC can a you actually get a safety certified product that as designed can draw more current than the way it is "plugged"? i.e. for a 20A circuit here a NEMA 5-20. My bet is it ain't happening.

 

[Rja4000]

Amir, can we get the 32-tone IMD test

Yes, I'd like to see that too.

 

[Vasr]

I wouldn’t make that assumption because there is a feasible explanation for the increase in gain (I.e., multichannel camp is designed for weaker outputting AVR/AVP’s ). I think a comparison to the Benchmark should be a yet to be designed/manufactured NAD “M23” (I just made up that name—I assumed it might be that for an NAD 2 channel purifi replacement for the M22).

The solution to that is to provide a gain control setting like the Benchmark or the Parasounds or any amp with pro-audio background where gain-staging is common.

The direct competitor to this is the ATI series AT527NC, a head-head comparison would have been great as to whether the additional $800-$1000 is worth it.

 

[Vasr]

The other class D alternative is the D-Sonic (Pascal modules) that can be configured in many different ways

 

[PeteL]

I'm assuming this performance will hold true for the M33 all in one box and the cheaper C298 power amp. Guess that solves my NAD v Benchmark conundrum.

This is the main reason I come here. Not for the Class AB trash talk, but because marketing departments shouldn't claim (or hint at) what they can't deliver.

We may know a bit more soon when amir pulls the top off, but I'm a bit puzzled by the assumption that a 7 channel amp should perform exactly like the "reference design" or any stereo amp. I know that the test is made with two channel driven, but still, all amps are on and biased. The review holds it's power with multiple channels, this is good, but can we really blame everything on the 2 dB extra Gain, as As @amirm said or to the fact that "they sacrificed noise and distortion for a few more watts" as @voodooless said? the "reference" power supply (or supplies) can't work for these 7 channels, nor the one in the Benchmark. It's a different amp not only for the input buffer, but also for power distribution, and for the power supply itself. We cannot draw conclusions that a 2 channel version would measure the same. As there should be a small but measurable difference between a mono block and a stereo amp using the same module, and yes, buffer gain change too, but it's my belief that overall performance, it's the sum of little things, not a single thing that we can so easily pinpoint and draw conclusion. It's the whole design.

 

[Beershaun]

This is a good point of reference to argue against those who are unnaturally obsessive about SINAD (95% of the members here).

20 bits is audio transparency. That should be the target. Especially when the reference design is capable of it and Dolby Atmos is capable of it. 16bits sounds like a cost savings decision. “It’s good enough for CDs and MP3s. Ship it!”

 

[zelig]

Sorry, but I have to say it...

Go NAD!

See y'all again at the next NAD review.

 

[restorer-john]

I don't think it's expensive for what you get. 7 very high performance amplifiers in a beautifully finished cabinet by a major manufacturer. If I needed 7 channels of top performing Class D, I'd put it on the list for sure. In Australia, it's MSRP is $7999. Almost good value.

@amirm Did you notice any differences between the various channels with repsect to their placement? Did you employ left and right channels at opposite ends of the unit or side by side? I presume they are identical vertical placement in the chassis. Is there any interaction between adjacent channels?

Gosh, not only do we have higher noise level but also much higher (in relative terms) distortion as power output increases relative to reference design. I did not want to believe this so to confirm my setup, I pulled the reference design and measured it again and its performance was unchanged (green). So this is definitely a degradation in M28 design.

The M28 delivers more power at lower distortion than the reference design according to your tests into both 4 and 8 ohm loads. The reference design may hit a lower distortion but hits a Po wall well before the NAD. NAD rate the amplifier 20-20KHz at less than or equal to 0.003% THD (and CCIF IMD, DIM 100) and its rated power output and THD appear to correspond perfectly.