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NAD M28 7 Channel Purifi Amplifier Teardown

restorer-john

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Can such failures blow speakers?
Unlikely. The Purifi modules attempt to shut down the power supply when they detect DC or have an internal failure that presents significant values of DC at the output.

On the other hand, a failure of one or more power supply secondary rails would result in the primary side switchers being disabled in most cases, so again it would be unlikely speakers would suffer.

Capacitors that fail in SMPSs usually go high in ESR, the electrolyte heats up, they vent and dry out rapidly. The value actually decreases and more and more ripple is present on the supply lines. It's a cascading effect. Digital circuitry starts glitching* or behaving strangley and eventually stops working altogether. Analog circuitry can tolerate deteriorating caps, but effects will be heard (more buzz and hum) A point is reached where the capacitor/s either explode and make a big mess, short and take out a heap of circuitry, or simply become a low value, high ESR, useless component.

*Everyone surely has had a modem or router run from an SMPS where this happens after 4 or 5 years of use. Usually it's the secondary rail filter capacitors in the sealed wall-wart SMPS or the onboard sub regulator smoothing caps.
 
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Dmitri

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Yes, I was discouraged enough by @amirm’s Performance and Teardown Reports that I finally just decided to sell the M28 immediately. I’ll take a ~$2,500 bath on that. I’ll count it as a good lesson regarding avoiding ”1.0” products. Entirely my fault.

Casey
OK. Maybe a stupid question(s), but if it’s such a concern can’t you just replace the PS caps with a better quality/ higher temp capacity brand? Certainly cheaper than losing 50%+ sales value on the consignment. If Amir’s opened it up, is not the warranty void anyway? How hard would this be to do?
 

TimoJ

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OK. Maybe a stupid question(s), but if it’s such a concern can’t you just replace the PS caps with a better quality/ higher temp capacity brand? Certainly cheaper than losing 50%+ sales value on the consignment. If Amir’s opened it up, is not the warranty void anyway? How hard would this be to do?
Changing caps (probably) won't make it perform any better. So if the owner can't live with below 100dB SINAD, there is only one solution...
 

Dmitri

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Note that I did eventually allow myself to be convinced to keep the M28 once @amirm is done playing with it.

My misgivings are those of an engineer, not "having listened to it", etc. As an engineer it always pisses me off when I see other engineers do substandard work.

Casey
In some cases...ignorance is bliss...; ) It appears to be a fine amp with a few caveats, just like most other fine quality amps. I’m pretty sure you’ll get years of enjoyment from it. Not sure I could do what you did, shipping your M28 to Amir for testing and tear down. Thanks for making this review possible.
 
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What you don't understand is when SMPS capacitors fail, they can and do take out everything before them and stuff downstream as well, often very spectacularly.
Would you advise preventive replacement of the capacitors of a new SMPS with high quality ones, John? For example in case of buying a new Hypex Class-D amplifier with accompanying SMPS?
 

carlob

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This is beyond ridicolous.

You don't change components in a brand new device, if you doubt the manifacturer circuit design and engineering, provided that you have the technical skills and the information needed to make such a judgement just don't buy the device. Btw you haven't and none of us have the info needed to make such assessment, cheap capacitors could last as expensive ones if the design has been done right, certain SMPS topologies sometimes fail because the designers took out a simple zener thinking it was superfluous, are you able to read the schematic - provided that you have one - identify the SPMS topology and look for a missing zener in the circuit. If you do, better you go work for NAD.

Different matter are manufacturers that have a history of faults due to cheap caps and probably inadequate electronic design. Before buying do your due diligence. But if you are not able to sleep because you think that a device may fail in the future just don't buy it, at this point don't buy anything.
 

carlob

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This is a stock Hypex NC500MP OEM (pic taken from the Hypex website). Capacitors are Su'scon, not exactly first tier right? So are we going to recap all the hypex amps, I don't think so.

1_nc500mp.jpg
 
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So are we going to recap all the hypex amps, I don't think so.
I think you miss the price comparison and that the NADs PSU is fully custom while Hypex PSUs are cheap and easily replaceable.

So the question of recapping doesn't even come to mind with the Hypex PSUs but it does with the NAD, and that is not a good sign for this price honestly.
 

carlob

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I think you miss the price comparison and that the NADs PSU is fully custom while Hypex PSUs are cheap and easily replaceable.

So the question of recapping doesn't even come to mind with the Hypex PSUs but it does with the NAD, and that is not a good sign for this price honestly.
sorry, I really don't follow. What does it mean "fully custom"? Caps in the Nad board are a special breed of non-replaceable caps? Do you think it is normal to buy a new device and replace the capacitors? Buy a soldering iron and good luck.
 

Francis Vaughan

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I think you miss the price comparison and that the NADs PSU is fully custom while Hypex PSUs are cheap and easily replaceable.
The device in the picture above isn't a cheap Hypex SMPS. It is their one of their mains powered Nc series amplifiers. There is no replacing the PS in one of these, it is a monolithic device.
The standalone board is only available to OEMs, but DIY customers can buy it attached to a mounting plate with an input module for 330 Euro as the FA501.
 
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sorry, I really don't follow. What does it mean "fully custom"?
I think you missed my argument. The PSU in this device was specifically designed and manufactured for the M28 exclusively. You can only get this part through NAD service and as long as they want to provide that.
The Hypex PSUs are cheap mass market parts that you can get everywhere as a normal consumer.
And the Hypex PSUs have the benefit of more common connectors and presumably future PSU products will be compatible with old connectors.
Of course it doesn't have to be only Hypex, I'm sure there are other manufacturers that provide similar products.

The device in the picture above isn't a cheap Hypex SMPS.
I know that thats why i said exactly "Hypex PSUs" like the ones i mentioned earlier in case you missed it.
And even if you wanted to replace this "fully integrated" NCxxxMP part you could do that pretty cheap and easy.

I was making a case that NAD could have used more commonly available PSUs from Hypex or other companies to make repairs cheaper and easier.
But they intentionally didn't do that to save some money on their custom part because of cheap components and force customers to come to NAD for repairs as well as give the device an end-of-service date when they decide to stop offering the repair service.
But even if they provide a long repair service window theres another issue: this design is probably only made by a single supplier and it will be uncertain if NAD is willing to go to another supplier and potentially change the design because the supplier can't produce the exact same design.
 
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This is beyond ridicolous.
You can call it whatever you want. I don’t mind a dying PS, it is easy to replace and not expensive. But I do mind loosing a complete amplifier because of a dying SMPS, and if replacing a few capacitors could prevent this I wouldn’t mind doing so. It is neither difficult nor expensive to do, and less far-reaching than modifying new cars. Which is what some of my friends are doing on a regular basis.
 

Billy Budapest

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Yes, I was discouraged enough by @amirm’s Performance and Teardown Reports that I finally just decided to sell the M28 immediately. I’ll take a ~$2,500 bath on that. I’ll count it as a good lesson regarding avoiding ”1.0” products. Entirely my fault.

Casey
You can’t be serious?
 
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There is no single Hypex SPMS able to supply power to 7 NC500 modules
If you don't want to understand thats fine... :facepalm:

One last try:
https://www.hypex.nl/img/upload/doc/smps/smps3k/Documentation/SMPS3KAx00_10xx.pdf
3000 Watt Output Power
The maximum number of modules which can be connected to the SMPS3k is limited by the output power of the SMPS. Please refer to the amplifier’s datasheet for more information.
You can connect as many amps as you want to it but you are limited to 3000 Watt Output.
That PSU is 290 € incl. tax single quantity end user price.

And please don't tell me the NAD M28 PSU can output 3000 Watts because it can't.
 

kn0ppers

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Just look at the format of the Hypex PSU, the whole NAD amplifier would have to have a deeper chassis. They probably had a fixed depth to work with because it's supposed to stack well with their other gear.
 
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