Sorry I am back again with this thread
. It was the Amir's review
This is a review and detailed measurements of the Audiophonics HPA-S400ET. It was sent to me by the company after member request and costs 1 490,00 € (US $1,638). I must say this is one of the best packaging of class D amplifiers (Purifi in this case) that I have seen! It is slick and has...
www.audiosciencereview.com
and especially this measurement
that has shown that even the best current class D module, Purifi 1ET400, suffers from quite severe high frequency non-linearity. Thank you
@amirm for performing this kind of @45kHz BW distortion vs. power test as a rule. I have decided to accept it as my standard test method as well and I have tested 3 of my amplifiers under same test conditions, the comparative result I have posted here in this thread:
Following the discussion in the Audiophonics HPA-S400ET thread on Purifi HF non-linearity, I have decided to make a comparative measurement of 3 of my amplifiers. THD vs. power into 4ohm with @45kHz bandwidth. The amplifiers under test are: 1) A250W4R, 250W/4ohm class AB amplifier based on...
www.audiosciencereview.com
The only difference from Amir's test is that I plot THD (without N noise component) vs. power so I can better see distortions at low level which would be masked by noise in the THD+N test.
The result with Hypex NC252MP module is this>
View attachment 196111
It is a bit worse than the Purifi result however similar behaviour. And the result is worse than the class AB amplifiers that I have measured and posted in the thread linked here above.
It is an ultrasonic distortion, you will say. Correct, The poor behaviour results from distortion components above 20kHz. Does it matter, or is it OK? Though 1kHz spectrum from NC252MP is nice, the 5kHz and higher are NOT nice. There are not only ultrasonic harmonics, but also non-harmonic distortion products, like
View attachment 196114
This cannot be compared to a very good class AB amplifier with clean spectra free of non-harmonic products. So, I am taking up the glove and walking against mainstream again
. At least raising an unpopular question. And asking the best class D designers, when are you going to get rid of such circuit behaviour???