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NAD M28 7 Channel Purifi Amplifier Teardown

PeteL

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Golly, I guess I ought to unload my NAD receiver. It's been working fine all the while but is more than 10 years old so I suppose will give up any day -- actually it's a 7130 receiver: 35 years old.
Yep, I still use a 2700 power amp on a B system. Still going strong.
 

Casey Leedom

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I hope this is sarcasm. It is, right? It's so hard to tell these days.
Uhmmm, no, not sarcasm. Why do you ask? It cost me ~$4,500 + tax, I probably won't be able to have it sold for anything more than $4,000 and there's a 40% consignment sale fee. Altogether, I may be able to recoup ~$2,500 if I'm lucky.

Casey
 

MakeMineVinyl

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I'd be more worried about the other way around tough. Wondering if there is a vertical PCB that we don't see between the two sections, but there doesn't seem to be temperature control, or any obvious micro controller. Even just a PIC. Does this amp ever turn off in case of over heating or continuous clipping? No evidence of a soft start circuit neither, altough it could be hidden in the PSU, I don't pretend to have a full fuctional understanding of all of it.
There appears to be a 20 pin PIC on a vertical PCB on the amp modules - you can see the ICSP programming pads right above it. I know that at least in the case of the Hypex modules, the temperature is monitored among other faults. It can be read out via the i2C buss from the modules. I assume the Purifi modules are similar.
 

Chromatischism

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Uhmmm, no, not sarcasm. Why do you ask? It cost me ~$4,500 + tax, I probably won't be able to have it sold for anything more than $4,000 and there's a 40% consignment sale fee. Altogether, I may be able to recoup ~$2,500 if I'm lucky.
Why sell it? What is it not doing for you other than cook breakfast? I'm curious because your post was very dramatic and I'm not sure why your use of the unit would suddenly change or stop working for you after it's tested here. Were you enjoying it before reading this review?
 

Vasr

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Typical NAD...these things are made to fail within 5 to 10 years. Sounds good while it lasts.
Shame for the usual Chinesium capacitor garbage and AGAIN deliberately placed at the heatsinks, they have been doing this for years.

Saw an M2 at the repair bench at a friend of mine's repair place. He gave it back to the owner stating it's not worthwile even looking at it, too much SMD crapola and already crusty soldering joints.

One should really look at NAD as 3 (or 4) different sequential companies sharing the brand name because they have gone through so many significant structural and organizational and philosophical (and even geographical!) changes over their history. Outlaw, I believe, was created by some ex-NAD people that developed philosophical differences with the company. Each of those "companies" have used different trade-offs in design and construction some worse than others. Each trying to survive in the tough market at the time.

The current company bears only a small resemblance to the others before it in focus, marketing approach or trade-offs. Financially, I believe the current company will do much better than the others before it with a marketing-led approach. But that won't necessarily translate into great engineered products. More of a system integrator type approach focusing on end user functionality and form and not necessarily tied to internal development of most of what is inside. A very different business model and perhaps a good one for survival.
 

Casey Leedom

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Why sell it? What is it not doing for you other than cook breakfast? I'm curious because your post was very dramatic and I'm not sure why your use of the unit would suddenly change or stop working for you after it's tested here. Were you enjoying it before reading this review?

It's actually my unit that @amirm tested. I've never actually laid eyes on it. After he returns it to the dealer I'll have the dealer sell it for me.

Casey
 

boXem

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It's actually my unit that @amirm tested. I've never actually laid eyes on it. After he returns it to the dealer I'll have the dealer sell it for me.

Casey
Will you loose 2.5k because a few people on a forum do not like one capacitor brand? Not my business, but doesn't seem very reasonable...
 
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amirm

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You can get Hypex PSUs like the 1200W SMPS1200A400 for 215 € tax incl. and the 3000W SMPS3kA400 for 290 € tax incl.
The Hypex power supplies use cheap caps too. And they are a source of failures there.
 

carlob

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It's actually my unit that @amirm tested. I've never actually laid eyes on it. After he returns it to the dealer I'll have the dealer sell it for me.

Casey

I would have expected better caps in a 5K product, that said if and when they fail they can be changed it's not heart surgery, can be done by any repair shop if out of warranty. Selling it at a 50% loss because of the caps is ridicolous.
 

HTNut1975

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Uhmmm, no, not sarcasm. Why do you ask? It cost me ~$4,500 + tax, I probably won't be able to have it sold for anything more than $4,000 and there's a 40% consignment sale fee. Altogether, I may be able to recoup ~$2,500 if I'm lucky.

Casey

I also just bought this. It is sitting on my living room floor, waiting to be installed. There is no way I’d sell it (especially at that kind of loss). If you bought yours for 4500 plus tax and your dealer is going to sell it for maybe 4K plus a massive consignment fee? That is not a good deal at all.

I would at least wait to hear back from NAD on some explanations for some of the measurements. But if you are that disheartened to sell, throw it up on Audiogon and you’ll recoup most of what you put into it.

Really, what better multichannel amp is there? This is an excellent multichannel and should last a long while and will have a very good resale value that will likely stay that way for several years. You could use this amp for the next several years and sell it for the loss you’re talking about.
 
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Vasr

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There is nothing really broken in this unit that you can get NAD (which has been dismissive before of reviews here) to acknowledge. At best they may silently improve the noise/distortion profile in a v2.

Moreover, I don't think any company let alone NAD is going to say anything about choice of caps. At best, it will be a boilerplate statement that they use the best parts that enables the "high standards" they are known for and that you should listen to it because that is the ultimate judge.

This is more of a expectation vs what is delivered issue and people can certainly have differences there. One may be happy with a car that does 0-60 in 4 seconds or looks sexy and overlook the bad plumbing or the more than expected interior noise. Some may expect their car to have great care in its engineering (especially if great engineering has been the brand reputation and marketing spiel) and be angry about getting a car with cheap injectors and hoses. Enough to get rid of it.

So I can understand Casey's feelings about it as well. In discretionary products including audio, pride in ownership is part of the equation and certain aspects may detract from that for some more than others.
 

martin900

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Golly, I guess I ought to unload my NAD receiver. It's been working fine all the while but is more than 10 years old so I suppose will give up any day -- actually it's a 7130 receiver: 35 years old.

The turning point for NAD (in the bad direction) would be around year 1995-2000, then the AV/T series started to appear and these were just rubbish.
I mean, even in the C300 series, there are low quality capacitors all around pretty much touching a hot regulator heatsink, while there is still plenty of room left on the PCB and around the tracks. They truly are designed for a certain lifespan.
 

Casey Leedom

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Well, a wise man once said — sadly, not me — if everyone and their dogs think you’re crazy, perhaps you should get into therapy.

So I’ll go ahead and accept delivery of the M28 and I’ll sell it later if “necessary”.

Just for background: I bought this sight-unseen (“ear-unheard”?) based solely on the engineering prowess of @Bruno Putzeys and the measurements that @amirm has made in the past on the various Purifi implementations. (Yes, that makes me an “Objectivist” I guess.) So to have the NAD implementation fall so short of the other implementations was a very big disappointment. And the only reason I was even in the market for this Unicorn (a well-measuring 7-channel amplifier) was because my 13-year-old old Emotiva MPS-1 has been getting flaky and I needed a new 7-channel amplifier (because of space constraints in my home).

Casey
 

PeteL

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The turning point for NAD (in the bad direction) would be around year 1995-2000, then the AV/T series started to appear and these were just rubbish.
I mean, even in the C300 series, there are low quality capacitors all around pretty much touching a hot regulator heatsink, while there is still plenty of room left on the PCB and around the tracks. They truly are designed for a certain lifespan.
I think we could agree that generally speaking, most for products being sold today, there is some truth to the fact that they don't last as long, and yes, we can see in a design like this some engineering choices that can potentially accelerate failures, but I think that going for the big conspiracy theories of pre planned obsolescence is a bit far fetch. Cost cutting measures, yes. Clearly, when you look at the mechanical assembly of this M28, it's clearly something made to be repaired, not disposable in an eventual failure. I believe that all manufacturers, except the the full cost no object, no compromise approach, all have to go trough their design, parts by parts and try to make it cheaper. This part is healty, it's much easier to make a design if you have zero cost restriction. Now yes cutting costs in a way that will not compromise performance beyond their specifications/performance goals, generally takes priority of extending the life span, True. but a company that don't make this exercice and just throw whatever is best and try to be competitive price wise will not survive. Still, this is not Apple here, this is Nad, Apple knows that when your phone is obsolete, you'll get another one. Nad knows that if their amps are unreliable, their reputation will suffer. Totally different. I'm not saying that they are immune to bad engineering choices, but they file it in the mistake drawer, It's not something they would want, to make your product die prematurely.
 

HTNut1975

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Well, a wise man once said — sadly, not me — if everyone and their dogs think you’re crazy, perhaps you should get into therapy.

So I’ll go ahead and accept delivery of the M28 and I’ll sell it later if “necessary”.

Just for background: I bought this sight-unseen (“ear-unheard”?) based solely on the engineering prowess of @Bruno Putzeys and the measurements that @amirm has made in the past on the various Purifi implementations. (Yes, that makes me an “Objectivist” I guess.) So to have the NAD implementation fall so short of the other implementations was a very big disappointment. And the only reason I was even in the market for this Unicorn (a well-measuring 7-channel amplifier) was because my 13-year-old old Emotiva MPS-1 has been getting flaky and I needed a new 7-channel amplifier (because of space constraints in my home).

Casey

I too was a tad disappointed with the results and I also based my purchasing decision for similar reasons as you, but I will wait on perhaps further explanation for why NAD chose to go the route it did to reduce the SINAD from even the M27 before I regret not grabbing an open box M27 when I could have.

At the same time, I’m not fully convinced that even with this slight reduction in SINAD that it is the worse of the two units (taking price out of the equation). Part of my reservation does have to do with listening to a couple of interviews from Putzeys about Purifi and reading others comment on the sound of Purifi (e.g., from @March Audio ). Now, would the increase in SINAD negate that? I don’t think so? But others here may be able to weigh in on that.
 
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PeteL

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I too was a tad disappointed with the results and I also based my purchasing decision for similar reasons as you, but I will wait on perhaps further explanation for why NAD chose to go the route it did to reduce the SINAD from even the M27 before it before I regret not grabbing an open box M27 when I could have.

At the same time, I’m not fully convinced that even with this slight reduction in SINAD that it is the worse of the two units (taking price out of the equation). Part of my reservation does have to do with listening to a couple of interviews from Putzeys about Purifi and reading others comment on the sound of Purifi (e.g., from @March Audio ). Now, would the increase in SINAD negate that? I don’t think so? But others here may be able to weigh in on that.
I'm just gonna say that it "behave" like the Purifi reference design. The distortion is a bit Higher, but it looks like the same distortion profile, just a bit more of it. A bit more noise too. The multitone test is superb. There is nothing wrong with this amp. Bottom line, they decided on a slightly higher gain, on a different power supply, and some compromise having to cram more amps in a limited space, more overall heat dissipation, they compromised a few dBs of Sinad, that they judged would not be audible. I don't think there's more to it.
 
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HTNut1975

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I'm just gonna say that it "behave" like the Purifi reference design. The distortion is a bit Higher, but it looks like the same distortion profile, just a bit more of it. A bit more noise too. The multitone test is superb. There is nothing wrong with this amp. Bottom line, they decided on a slightly higher gain, on a different power supply, and some compromise having to cram more amps in a limited space, they compromised a few dBs of Sinad, that they judged would not be audible. I don't think there's more to it.

Out of curiosity, is it possible that some of the same model amps test a point or two different from others? For example, is it possible that the M27 @amirm tested one of the better ones out of a batch? Seems like these all could vary a tad here and there.
 

PeteL

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Out of curiosity, is it possible that some of the same model amps test a point or two different from others? For example, is it possible that the M27 @amirm tested one of the better ones out of a batch? Seems like these all could vary a tad here and there.
I doubt that, half a dB different Sinad between different samples, maybe. Not 3 Their own quality control would catch that. Again the power test with 5 channel driven has not been done on the M27, maybe it would have performed equally, maybe not but just that is a very good performance score on the SMPS they chose/designed. Sometime you gain on some areas, loose on others. Just design choices, in my humble opinion
 

Chromatischism

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Generally the more amps you put into a case, the more SINAD goes down. At least that's what I've seen. I wouldn't expect this to perform the same as a one or two-channel reference design. And, as far as I know there aren't any other 7-channel Purifi amps yet, so there's nothing to compare this to.

The comparison to the M27 is probably a valid criticism though.
 
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