NAD M28 7 Channel Purifi Amplifier Teardown

[Michael YYZ]

I should’ve posted this here:

https://www.audiosciencereview.com/...er-amplifier-review.15939/page-10#post-513942

 

[Michael YYZ]

That should be the relay which switches the input between balanced and single ended.

@amirm
out of curiosity, did you identify the large silver rectangle up the rca plug? Looks like a shield. Transformer?

 

[PeteL]

That should be the relay which switches the input between balanced and single ended.

right, make sense.

 

[Michael YYZ]

[email protected]

Sure. I tried to find an email address but it was hard. I finally found a support line and sent them a message. Hopefully it gets to the right person and they respond.

 

[PeteL]

While extracting a pretty penny in royalties from NAD who are forced to use their lunch money to pay for their caps.

Maybe in the past they had some deal with nad that was Licence/Royalty based because of mention that Nad where making slightly modify ones, but this here looks like the modules themselves. Unless something is special with Nad, Hypex/Purifi had and have, as far as I know an OEM business model. They shouldn't get royalties, You buy the number of modules you need and they are yours to use. That said I won't pretend I know the exact deal behind, but generally that's how they operate. Maybe Purifi isn't exactly like Hypex neither.

 

[Michael YYZ]

Correct. Mine is rated for 100-240V ~ 50/60Hz 1200W (written on the back panel).

I find a clearer picture on the internet, and it's rated 1200W, I would still like to know how they calculate this, but I never ran into a problem following these. So basically, a dedicated circuit, maybe, but it wouldn't be unsafe or problematic to add things on the same circuit that don't pull more than 240 extra Watts, unless you are running the same test as Amir for minutes.

 

[gvl]

That 80% rule is for a continuous load. So for me when I charge my EV I can only pull 40A on my 50A 240VAC circuit. I think you can make the argument that this device doesn't present a continuous load.

That's the reason that most "1500W" hair dryers in the US actually only draw 1200W.

The 80% continuous rule is mainly there, afaik, to prevent nuicance breaker tripping, as if you pull 50A through a 50A breaker it will likely trip over time. Wires rated for 50A will let 50A through all day long.

 

[digicidal]

@amirm Give it a go. Do you feel lucky? (I would totally do it, each amp has comprehensive protection. I wonder what two Purifis bridged would hit into 8/4R?)

I picture you in a devil cape and horns whispering this in @amirm's ear while standing on his shoulder. Maybe time to change your nick to "destroyer-john" instead? LOL

 

[carlob]

 

[Koeitje]

It always saddens me to see low quality caps. You would expect a product like this would be built with durability in mind. When I see PC PSU's it is always 100-105C caps in there.

 

[wwenze]

Lelon caps are good enough... to last the warranty period... nothing more...

 

[TimoJ]

@amirm what about those 6 big caps on top of the picture, are those also Lelon? Their negative pole marking looks different from Lelons. And the smaller ones on the PCB, who made those?

 

[bobopich]

I was about to purchase it, but now I think I'll keep my M27 for a little longer

 

[Daniel0]

It seems like the worse performance of NADs M28 purifi amp comes from the use of cheap parts in many places?
Like others already mentioned I'm concerned about the low quality capacitors especially in the power supply. This seems like a strong case of planned obsolescence, not really fitting for this price range in my opinion.
And the fact that it's a custom single PCB power supply purely for this amp makes repairs hard and expensive. If NAD decides to discontinue the PSU from their repair service this amp is probably scrap.
The choice of a custom PSU is probably another cost saving decision, since Hypex offers many PSUs for various use cases.

Maybe someone can explain what the second opamp "Microchip MCP6002" exactly does in this design? The LM49720 seems like a pretty high quality part but the MCP6002 seems like super lowcost as my search purely based on the pricing of the two suggests.

 

[Kal Rubinson]

Based on this amplifier's design, you could just for fun (and if you were brave) use the already opposite polarity channels, drive them with a common signal (Y splitter)

We did this with the M22.

 

[YSC]

It always saddens me to see low quality caps. You would expect a product like this would be built with durability in mind. When I see PC PSU's it is always 100-105C caps in there.

Exactly, and even a top end pc don’t cost that much

 

[audioBliss]

I expected this to blow the nCore stuff out of the water frankly. Sticking with nc502mp/252mp for surround duties.

 

[Tks]

It's interesting they decided to use Lelon brand low cost capacitors in a $5000 amplifier instead of spending a few more $ and get Nichicon or some other respected Japanese brand of capacitors. Especially considering it's a switchmode power supply with high ripple current where the capacitors get quite a workout.

Whats up with luxury companies being unable to even put at least top tier parts in their devices? If it's anything I would expect in the very least, it's that they do that.

 

[Koeitje]

Exactly, and even a top end pc don’t cost that much

Well, a 1600W Corsair PSU is like €500-600. But you do get quality:

With higher end components like GaN transistors and 100% 105C rated Japanese capacitors, as well as the FDB fan, you'll be able to rely on the AX1600i for your builds for years to come. And our 10 year warranty gives you peace of mind.

10 year warranty is some good stuff.

 

[bigguyca]

Note: I'm just some engineer who now makes software that rewired his whole 1925 house a few years ago. So, take this with a big ole grain of salt since I am not an electrician or NEC expert.

The NEC has an '80%' rule, though I don't know how strict it is, or if it would even apply here.
https://www.electriciantalk.com/f2/80-rule-67638/

I think the general idea is that you can use up to 80% of the circuit/breaker in practice e.g. 15 amp breaker/circuit can use 1,440 watts (15*120*0.8).

In your 5 channels load test in the original review you were drawing around 1,455 watts (262*5/0.9, assuming 90% efficiency)!

The purpose of the 80% rule seems to be for long term continuous loads, like hours. So it's unlikely to cause an issue here,you can likely get more out of this unit than that in practice. It does make me think that a dedicated circuit would be a good idea.

In this context a continuous load is a load for three hours or more. AV equipment is unlikely to violate continuous load limits. Items such as hair dryers and toasters are also unlikely to violate continuous load limits.