Review and Measurements of Purifi 1ET400A Amplifier

[pozz]

I haven't been following this thread very closely—has the price for the reviewed module been officially released?

 

[Killingbeans]

No info on purifi-audio.com so far. At some level I feel like driving to Roskilde, sleep in a tent and protest holding a cardboard sign saying "Free the 1ET400A price!" until they tell me

 

[Audiocrusader]

Just got the new Purified Nords. I did not get a chance to listen (and with my current work load it may take a while ...) but I did manage to open them up and take some pictures.

What is most interesting, is that the Purifi modules show some 20 deg celsius lower working temps than the Ncore ones. They still run hot at idle, but not just as hot.

Here are two amps side to side:

Purifi top
NCore NC 500 bottom

View attachment 34873

This pic doesn't is not accurate enough, but the NCore modules get as hot as 68'C (154 degrees Fahrenheit). By far the hottest component is the coil:

View attachment 34874

Purifi on the other hand maxes out at 50'C (all temps at idle with the tops open), with the hottest components beeing that vertical daughterboard an a chip next to it.

PSU transformer, Sparkos discrete voltage regulators on the input board also reach 50'C.

View attachment 34875

Purified Nord inside:

View attachment 34876

Purifi board (here you can see the vertical doughterboard that gets so hot and the long chip next to it; the coil on the other hand is warm, but not hot to the touch):

View attachment 34877

So 1 guy on this thread has owned a Purifi based amp for over a month, but no feedback yet. I asked about it on his Audioshark thread but the moderators won't approve the post. I guess the dealer running the Audioshark forum doesn't want another runaway thread about a Nord class D amp.

 

[Victoria]

I haven't been following this thread very closely—has the price for the reviewed module been officially released?

Yeah, given how crap the SNR of this thread is, I don't think anyone can be blamed for not following it too closely haha.

Having said that this is a module I'm also immensely interested in and I'm still very much curious how they'll be pricing it against say the Hypex Ncore 400 and the various offerings from ICEpower. Also curious as to its long-term reliability, but that's a test for time to conduct though I don't see any reason to believe that the Purifi is anything other than supremely engineered.

I've got no experience with Hypex but ICEpower modules seem to be pretty much bombproof.

 

[maty]

https://www.diyaudio.com/forums/vendor-s-bazaar/281361-hypex-ncore-nc500-build-post5957532.html

by daanve

Bruno (finally) discovered the cause of the weak point of Ncore. The poor hysteresis behavior of the output coil is responsible for what he calls a "granularity" in sound.

It is what I'd call a certain "cloudiness" in sound when listening to an Ncore based setup for longer times. In a recent AES presentation he demonstrated what is going on (feed back not being able to "correct" hysteresis distortion). In his Purifi amps the output coils will have better quality core material...

 

[veeceem]

https://www.diyaudio.com/forums/vendor-s-bazaar/281361-hypex-ncore-nc500-build-post5957532.html

by daanve

So... Is this a bad thing for Hypex Ncore, SQ-wise? My order of NAD M22 v2, which based on Nc400 with Nc500 output stage, is on the way ....

 

[GrimSurfer]

So... Is this a bad thing for Hypex Ncore, SQ-wise? My order of NAD M22 v2, which based on Nc400 with Nc500 output stage, is on the way ....

I can't answer your question but the issue of feedback being unable to keep up at higher frequencies has always been an issue in amplification, Ncore or not.

 

[veeceem]

I can't answer your question but the issue of feedback being unable to keep up at higher frequencies has always been an issue in amplification, Ncore or not.

So, he just mentioned it to make Ncore seems worse because Purifi is about to be released to the mass?
And what he means by "listen for longer time?"

 

[GrimSurfer]

So, he just mentioned it to make Ncore seems worse because Purifi is about to be released to the mass?
And what he means by "listen for longer time?"

Some say that subtle issues in SQ manifest themselves more as "fatigue" or graininess over time, whereas large issues affecting SQ are immediately noticeable.

 

[dwalme]

Where in the measurements would this show up?

 

[maty]

Purifi Audio - A Straight Wire to the Soul of Music, October 23 2019
https://www.audioxpress.com/article/purifi-audio-a-straight-wire-to-the-soul-of-music

After a long and winding road, Putzeys finally found a culprit: hysteresis in the ferromagnetic material of the amplifier output filter coil...

Figure 1: The magnetic flux depends not only on the point on the BH curve, but also on where at which point you were before — there is a memory effect of sorts.


Updated

[ So there is an element of hysteresis, memory if you like, which causes strong nonlinearity. Although the feedback loop decreases all nonlinearities it encloses, if the error is large enough it can make itself heard in the output signal. This also suggests the solution: just increase the loop gain (that is, the amount of feedback)!

The crux for increased feedback is a tailored compensation loop, but to be able to design that you need to be able to model how the amplifier (and its output filter with the output coil) varies in gain and phase at any load and any level within its working envelope, and adapt the feedback/compensation loop accordingly... ]


https://www.diyaudio.com/forums/class-d/321578-phase-shift-class-amplifiers-affects-sound.html

Phase shift:

* PURIFI 1ET400A: only 1º at 20 kHz.

* Hypex NC400: amirm -> about 16º - 17º at 20 kHz. NC500 must be the same.

Updated, Nov 17

https://www.audiosciencereview.com/...-dual-mono-stereo-amp-review.9938/post-268273

Corrected results of Hypex NC400 is much worse!!!

https://www.audiosciencereview.com/...ments-of-hypex-nc400-diy-amp.5907/post-132771

First measurements: about 16º at 20 kHz. Corrected: 41º at 20 kHz.

 

[boXem]

Aparently problem solved with even more loop gain.

I can't answer your question but the issue of feedback being unable to keep up at higher frequencies has always been an issue in amplification, Ncore or not.

One of the strengths of the self oscillating class D (at least Hypex) is that their loop gain is flat over frequency. Instead of avoiding self oscillation of the amplifier, you want it. It opens a lot of new possibilities for the loop and the distortion profile obtained

Where in the measurements would this show up?

That is a good question. I would think HF IMD. One should compare NAD M27 measurements to 1ET400 to see if something shows a different behavior.
.

 

[Hayabusa]

Purifi Audio - A Straight Wire to the Soul of Music, October 23 2019
https://www.audioxpress.com/article/purifi-audio-a-straight-wire-to-the-soul-of-music

Some say that subtle issues in SQ manifest themselves more as "fatigue" or graininess over time, whereas large issues affecting SQ are immediately noticeable.

Figure 1: The magnetic flux depends not only on the point on the BH curve, but also on where at which point you were before — there is a memory effect of sorts.

I see a NC400 modding topic coming up....

 

[boXem]

I see a NC400 modding topic coming up....

Modding what?

 

[Hayabusa]

Modding what?

The output coil

 

[Julf]

Modding what?

Supposedly changing the output choke.

 

[boXem]

Supposedly changing the output choke.

My little finger tells me it's not that simple

 

[Willem]

Usually modding is another word for snake oil. I doubt the problem is anything other than audiophile hypochondria.

 

[Julf]

Agreed.

 

[veeceem]

Problem is: is the mentioned problem in Hypex Ncore audible? Or just something mentioned to raise interests in Purifi???