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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
madavid0 OP
214 posts
 
@djones I'd definitely be willing to do a blind test, but understand that's a pretty tall order when we're talking about comparing amps. In reality your requirement for blind testing is just a roadblock to protect egos and confirm biases. Listening impressions are fake and the correct method of conducting them are too difficult to achieve in everyday life, so you can remain comfortable in willful ignorance.

For example, in my ASR thread about Purifi, I noted that my reference mains cable chain had no effect. Responders agreed with this finding. Strange, shouldn't this sighted, unscientific listening impression also be invalid? How do I know there isn't an difference between mains cables? Maybe the lack of difference is just in my head, ie, I expected to change so I heard none? Funny. Weird. How does the requirement for blind testing disappear when the results conform with negative expectations? Of course because the responders just want to have their biases confirmed, the requirement for blind testing, ABX, etc, is just a tool to support the bias.
djones51
4,947 posts
 
If you don't like the amp return it and move on. The stock opamp is perfectly fine on the purifi boards you wouldn't be able to tell the TI from the sparkos or the silly tube contraption anyway. I don't have a bias I can't tell an Ncore from a purifi from a Pascal from a McIntosh SS amp. 
madavid0 OP
214 posts
 
I've been told by experienced audiophiles here and elsewhere that the default Hypex board is junk, so in order to give it a fair shake I ordered a set of custom ones from VTV. I think it's pretty obvious I'm not doing this just to make you feel bad about your support of class D / Purifi. I got the cheapest base unit to begin with because I figured there wouldn't be a substantial difference and at least I'd get a baseline grasp of the sound. I'm told that's not the case and the default configuration is compromised. Listening to the awful midrange I can see that there MAY be truth to that statement. Also it might be just that the artifacts are most noticeable in the midrange and that it's impacting the whole audio band. If these custom boards and opamps fix the issue and elevates the sound, I will faithfully report it. If it doesn't, then back it goes.
georgehifi's avatar
georgehifi
10,312 posts
 
I’ve been told by experienced audiophiles here and elsewhere that the default Hypex board is junk
Any one that says that is junk themselves and needs to be committed.
I’ve shown what the Hypex board is, it’s opamps may not be the "absolute very best" of opamps, but they’re not far off it. Anyone that can hold a soldering-iron can build one. And you’d have to be an absolute idiot to stuff up a buffer design using them. And I doubt Putzey is one.
https://forum.audiogon.com/discussions/purifi-class-d-junk/post?postid=2080260#2080260

Cheers George
yyzsantabarbara
4,865 posts
 
I've been told by experienced audiophiles here and elsewhere that the default Hypex board is junk
You  also need to ask them about their last hearing test just so you have a proper baseline. There are some pretty good class D out there.

My Peachtree Nova 150, while not as good as my current gear (BM AHB2), was a very good Class D integrated. I now wish I did not sell it since I need an integrated today that will sound good with KEF LS50's and can also tolerate some toddler abuse.

The Purifi Class D is what I am likely going to get for this new requirement but it will cost me more than the Peachtree.
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