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Purifi Class D: Junk?

So, from the previous thread about high-end class D the Purifi module was brought up. I decided to get a cheap example from VTV, a simple stereo unit with a single Purifi module and matching Hypex SMPS. Standard input buffer. I got it in yesterday. First impression wasn't what I was expecting: weak, congested dynamics is what stood out to me. I expected greater expression through my ProAc D30Rs. The other problems such as poor soundstage, thin / boring character, etc, I marked up to needing burn-in before evaluating. So it's been 24 hours, I would still expect to get at least the high control / damping of high end class D and dynamic power, but it's just not present.

Could it be an impedance mismatch? Other manufacturers selling the Purifi with their custom input buffers are reporting 47k Ohms. VTV doesn't say in the manual or on the site. I checked the Purifi data sheet which reports...2.2k Ohms on SE???? That can't be right?? That's absurdly low! Am I reading the right spec? My preamp has an output impedance of 230 Ohms. Can someone confirm that the stock Purifi has this ultra-low input impedance?
madavid0
twoleftears's avatar
twoleftears
5,318 posts
 
Yet another derailed thread by a few perennial posters who keep on repeating the same things, over and over and over and...  At least this one wasn't much of a loss, because of the false initial proposition on which it was based.
georgehifi's avatar
georgehifi
10,312 posts
 
Ask him for concrete evidence on Class D stuff, and he will cry uncle and start posting Nelson Pass’s quotes.
Shows what you know, think before you show your lack of................
That’s for an entirely different audio product not class-D. Stuff I post on Class-D’s Achilles-heel has to do with switching frequency and it’s filter and noise

But seeing you bought up Nelson Pass’s quotes, here are his on Class-D, that I’ve never put up.
Nelson Pass (Threshold, Passlabs)
"Does a $10 bottle of wine compete with a $100 bottle? Of course it does, and it often wins based on price. Right at the moment Class D designers seem to be still focusing on the objectively measured performance of their amplifiers. I expect that at some point the economics of the marketplace will encourage them to pay more attention to the subjective qualities, and then they will probably play a greater role in the high end."

And just for good measure Conrad Johnson
Lew Johnson (Conrad Johnson)
"I tend to think that Class D circuit design is an approach best relegated to producing low-cost, physically manageable multichannel amplifiers—where one might accept some compromise in sound quality for the sake of squeezing five, six, or seven 100 watt channels into one moderate-sized package for a budget home-theater installation."


Cyrill Hammer (Soulution)
"if you want to have your product performing at the cutting edge it is not possible with today’s known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz."

And there are quite a few more, if you want me to keep going?

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
because of the false initial proposition on which it was based.
Sez you, he has a valid but crude way of putting it.

Technics so far with the SE-R1, are the only ones that have addressed the Achilles-Heel of Class-D.

Output Filter, Noise, Phase Shift. All related to the Switching Frequency.

By utilizing GaN Technology to it’s fullest, and having (3x higher) Switching Frequency, and eliminating the 3 Achilles Heels above from effecting/influencing down into the audio band frequencies.

Cyril Hamer of Soulution- Audio at the bottom of my last post says it also.

Cheers George
madavid0 OP
214 posts
 
So, burn-in continues. There's a troublesome mid-range artifact, a harshness / blurriness that shows up in voices with "hot" recordings. Also the image seems to project especially high, but I'm not sure if that's the amp or something with the speakers because I did move them yesterday. If this midrange issue doesn't fix itself with continued burn-in then it'll have to go back as I know this will kill it for me, it's very uneuphonic. Maybe a custom input buffer option fixes it if this continues to be a problem, we'll see.
twoleftears's avatar
twoleftears
5,318 posts
 
From the OP's previous thread.
"So....I think I'll buy a VTV Purifi. I suspect I'm heading for disappointment again"
This thread is about as unbiassed as the Star Chamber ever was.
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