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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
georgehifi's avatar
georgehifi
10,312 posts
 


I’ve repaired a few Naim 250’s, the best was the first model with regulated rails back in the 80-90’s and they weren’t that good, they all oscillate at a drop of the hat, don’t think it would take much to beat them. If fact Naim dealers warned against putting them together with Quad ESL’s. And in the 80's Tocord speaker cable made them blow their guts.

Cheers George
madavid0 OP
214 posts
 
Okay so, update on the VTV.

The horrible midrange seems to have mostly solved itself. That's good. There is still a smearing / lack of resolution when things get busy. Midrange sounds -- instruments, voices -- still don't sound really convincing. Another troublesome aspect is that I don't seem particularly interested in long listening sessions. Lack of engagement. This could be a sign of a general lack of euphony which is the kiss of death of anything in my system.

Imaging and soundstage has improved since the early days, but it's still not really convincing. 

Bass however has improved to the point that I'd usually associate with class D. Dynamics have also improved to a level I'd call satisfactory.

Next step I think I'll contact VTV and ask about what changes the input board and buffer options may have. Perhaps a double power supply model will help. If some combination can help midrange I may try that.
jaulbrich's avatar
jaulbrich
22 posts
 
What did you expect from a low budget amp?  Compare a high end class D implementation against your high end AB and then let's talk...
cal3713's avatar
cal3713
1,421 posts
 
*sigh*
gkr7007's avatar
gkr7007
153 posts
 
Madavid0

Just as a bit of info.  Klaus builds his amps at 22 kohm impedence.
Not 47.
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