2. amps-preamps
  3. 162284-76532

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

Showing 15 responses by djones51

djones51
4,947 posts
 
If you don't like the amp return it and move on. The stock opamp is perfectly fine on the purifi boards you wouldn't be able to tell the TI from the sparkos or the silly tube contraption anyway. I don't have a bias I can't tell an Ncore from a purifi from a Pascal from a McIntosh SS amp. 
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. 
djones51
4,947 posts
 
I tried a VTV purifi amp months ago but sent it back. It actually sounded fine but the workmanship was a bit lacking and I didn't feel like cleaning the thing up.
djones51
4,947 posts
 
But it's not 2.2kohm. That's the OEM amp module without a buffer board.
djones51
4,947 posts
 
The 2.2kohm is single ended input to ground, what the amp sees. That’s simply the amp module without an input board connected. The evaluation board that manufacturers use on the amps has a 10.2kohm differential input impedance. In other words you need to know what board VTV used to know what impedance the preamp sees.
djones51
4,947 posts
 
You're banned because you're a troll. You take a product this time purifi and carry on as if you've done something by buying the cheapest amp you can find and complain about it in subjective terms. How many blind tests did you do? I doubt you could tell this VTV amp from an old crown in a blind test. Get real noone here takes you seriously either.
djones51
4,947 posts
 
My theory has already been tested, none could tell a difference. Better luck next time.
djones51
4,947 posts
 
I assume these various opamps are being compared sighted, I doubt in a blind test anyone could tell one from another. 
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. 
djones51
4,947 posts
 
This past year , which I've had a lot of time,  I've listened to various class d amps. I have no idea what opamps were used but I couldn't tell which was which in an unsighted situation. One was actually a class A/B amp. Not a proper test I know. I guess I don't have golden ears.
djones51
4,947 posts
 
I'm using a class d amp now. I have no idea which amp it is, ICE, purifi, Hypex Pascal, I've heard them all in different amps and active speakers. Since the room and speaker contributed more to the sonics than any amp or DAC ever could I wasn't really surprised. 
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.
djones51
4,947 posts
 
They charge it because someone will pay it. 
djones51
4,947 posts
 
I don’t think there’s anything wrong with the amp unless he messed it up popping opamps in and out. Try a blind listening test and get back with the results.
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