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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
jaytor's avatar
jaytor
742 posts
 
@douglas_schroeder - I don't think you read this thread very carefully. This isn't about DIY (although I don't personally share your skepticism about DIY). The OP purchased a commercial product using the Purifi module, a basic SMPS and cheap input buffer, and is blaming the Purifi module for its disappointing sound quality instead of the surrounding parts and overall design. 

That's like saying all DACs that use the ESS9038 are crap because a $79 AliExpress special sounded mediocre. 
ricevs
1,449 posts
 
I talked to Warren at VTV last week and he told me he has the Purifi eval boards coming in. He told me that he would sell it even cheaper than the Hypex boards because he was not going to use any input or output connectors.....just what is on the eval board. He will have a smaller chassis that will fit the eval board perfectly. The Purifi eval board version would be something like $50 less than what the Hypex board one is. A lot of people told him they wanted the Purifi input board....so that is why he is doing this. This "Purifi input buffer board" version will never be able to be upgraded to the custom VTV input buffer boards (that use discrete op amps).....Again, this is for people who want the cheapest thing possible and do not want to upgrade, ever. Basically, this will be very close to the eval. amps that Purifi sent out.....but for way less money than you can even assemble them yourself by buying the parts from Purifi, Hypex and chassis from China, etc.
mrdecibel
2,898 posts
 
Using King Crimson's track to make a final evaluation ? Ridiculous. A very processed recording. Try the works of Tony Minasian. Reference quality demo material, for sure, then, make up your mind.
madavid0 OP
214 posts
 
I didn't use the King Crimson as the final arbiter, it's just that when I heard the VTV blur the chime percussions into a mess I got angry and decided I was done. I'll look into this Tony Minasian.

But, once again, I've been talked into trying something. I ordered a pair of input boards from VTV with Sparkos opamps. I do appreciate the speed of VTV's responses. If the defeault Hypex board is really that compromised I thought I should give it a fair shake in a configuration which is it supposed to use. I don't get why Purifi thought this thing sounded good enough to release to the public but...oh well. They're coming.
georgehifi's avatar
georgehifi
10,312 posts
 
If the defeault Hypex board is really that compromised
I’ve got those those Hypex buffer boards in my NC500 mono’s that have my own big linear supplies, there’s nothing wrong with the buffers (they don’t sound bad as some here would like you to believe) Your problem is elsewhere.

Saying that, my MSB discrete R2R dac has got volume control in the digital domain with up to 5v out balanced, and by-passing the Hypex buffers altogether and going direct from the MSB's balanced output into the balanced input of the NC500 modules, the sound took on a massive improvement in transparency/dynamics and slam.

(Moral of the story: Less is more, just like I always say with passive pre’s vs active pre’s also when possible)

Cheers George
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