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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
 
I never said I tested the theory. I see no reason to educate anyone on sighted bias. The only way anything claimed about opamp sonic differences is if they were tested in a proper controlled blind setting. Flowery subject anecdotes while highly entertaining gives no valuable information. Thanks for playing. 
t_ramey
632 posts
 
douche51 strikes again
jaytor's avatar
jaytor
742 posts
 
@djones51 - if you don't trust your own ears and your ability to overcome sighted bias, that's fine, but telling everyone else that they are wrong is pretty arrogant. 

In my past experience with the Nord Hypex NC500 monoblocks using the Sparkos and Sonic Imagery opamps, the differences were pretty obvious. Once both were well burned in, I switched back and forth a few times and had a couple of friends over to listen as well (who didn't know one from the other). The Sparkos opamps were smoother and slightly warmer sounding, but clearly lacked detail relative to the Sonic Imagery parts. 

So far, I have only heard my Purifi amps with the Neurochrome buffer board which uses integrated op-amp chips (not discrete). There are pros and cons to both (IC vs discrete), and this is probably not the proper thread to discuss those. But I would like to hear how my amp will sound with different buffer designs and will eventually give one or more a try. 


djones51
4,947 posts
 
So, let me see...mentioning that sighted bias is a well know condition of all humans is arrogant? You're claiming you have an ability to overcome perception biases? Interesting. 
audio2design
1,351 posts
 
While on one hand, op-amps in the same circuit can sound different, which often says far more about the circuit than the op-amp, anyone claiming to be immune to sighted bias is delusional. If you can't be honest with yourself?

Circuits need to be tuned to a particular op-amp for best performance, so I always take with a grain of salt op-amp swaps.
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