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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
mike_in_nc
1,121 posts
 
@jaytor -- You have a wonderful touch with the DIY projects. If I had the skill and patience to make things so neat and beautifully laid out, I’d be a DIYer myself.

As someone interested in those PuriFi modules, I’ll be very interested in how you like the Weiss op amps. Please do post and let us know.

I believe the Weiss are not plug-compatible with the Sparkos and Sonic Imagery units. Is that right?
jaytor's avatar
jaytor
742 posts
 
Thanks Mike. I believe the Weiss opamp is pin compatible with the Pro series opamps from Sparkos and Sonic Imagery, but not their dual discrete opamps. 
I want to give my amps a couple more weeks of burnin before I decide how to proceed with the Weiss opamps. 
audio2design
1,351 posts
 
What an entertaining thread. A bunch of people (mainly) with obviously from this thread and others weak engineering skills (at best) with odd exception pumping their chests and egos while arguing about things they poorly understand while making wild and patently false claims about all kinds of things.

w.r.t. the purifi and hypex modules they need an input buffer to operate to specification. They cannot just be driven with a "lowish" impedance source.  They are meant to be driven with a very low impedance source, i.e. like the buffer circuit on the eval boards.  It sounds like the ops supplier is not qualified at what they are supplying.
ricevs
1,446 posts
 
VTV supplies the amps with various input buffers.....all of which drive the Purifi module with super low impedance. However, they all sound different.  Yesterday, I A/Bed the Weiss op amps versus my custom modified Sparko Labs 2590 op amps......different but in the same league.  Stock, the Sparko is not in the same league at all as the Weiss.  Everything you do makes a difference.  A complex game this is.
ctbarker32
8 posts
 
My videos about VTV have been popular. Also check out my Roon - 10 things you don't know video.

VTV Purifi Amplifier - Input Buffer Upgrade Video
https://youtu.be/Jj1jJPuda8A
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