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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
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. 
ricevs
1,543 posts
 
And thank you for playing.  However, the only thing worthwhile are subjective listening tests.......and they don't need to be blind.  But, I value your incorrect opinion.  I can remember how something sounded 10 years ago.....really!  Some do not believe/trust their ears and think that a blind test must be done.  Most all audiophile tests done by most all magazines and most all audiophiles (99%) are done without blind testing.   Maybe those that need blind testing are also deaf......he he.
audio2design
1,351 posts
 
georgehifi8,489 posts02-17-2021 7:10pm
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


No, it is not, especially with the Hypex amps.  The input is meant to be driven by a very low impedance source. The input of the unbuffered amp is essentially in the feedback path. Not having a local buffer is a recipe for doing it wrong.  This is the difference between people who actually know what they are doing and those who do not. People who do not make statements like this above.

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