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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
 
In my past experience with the Nord Hypex NC500 monoblocks using the Sparkos and Sonic Imagery opamps, the differences were pretty obvious.
Best is no buffer at all, direct in, as I’ve done. (you don’t need a buffer driving another buffer)
If the output buffer in your source (pre or dac) is less than <50ohm output impedance and has high enough voltage output gain to give the volume you need, you’ll have better sound than any additional buffer (regardless of how good) that’s in the signal path

Cheers George
jaytor's avatar
jaytor
765 posts
 
@djones51 - are you in the audio business? If not, why do you bother to listen to lots of different amps if they all sound the same to you?
djones51
4,947 posts
 
Boredom, I’ve heard more amps this year than my previous 30. Sighted they sound different, unsighted I couldn’t pick one from another. I should say even unsighted I can hear subtle very subtle differences but know which was which?? Nope
djones51
4,947 posts
 
I should also point out these were not proper controlled tests and the subtle differences could be attributed to other factors than the amps. Mood, change in sitting position, not all done with same speakers. I really have a hard time understanding how a huge difference in sound claimed by many in these similar designed electronic components can be discerned over room acoustics and speaker distortion which is a lot more than any amp unless it’s design is purposely introducing it.
mapman's avatar
mapman
22,277 posts
 
What’s the input impedance and the output impedance of the preamp?  Is it a tube pre-amp?   Impedance mismatch is the common cause in my experience when what you describe occurs. Not familiar with that specific amp though I would suspect  it can’t be that bad when matched properly to preamp. 
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