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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
oldhvymec
5,101 posts
 
Ok I looked at my Nords and my phone pics. I deleted the pic of the boards after I returned them..

Now I remember the whole deal. I bought 2 buffer boards and 2 Wiess opamps. They arrived but it took 4 opamps to do 2 boards. It was worded weird. I looked the boards over, and he (whoever built the boards), didn't use copper foil resistors and the work on the boards was not as nice. Plane and simple. 

I didn't get to listen to the Weiss, as I recall. I was ticked that I need two more. 950.00 for a pair.. 700.00 for the Nords..

The boards side by side, LOL yea, about that... VW vs Porsche.
The boards I looked over..
Even Rev C had copper foil resistors vs Weiss with cheapos.

They can take the 2590s I was mistaken, I was ticked the it took 4 Wiess Op Amps and he sent me 1/2 what I needed. Didn't make any sense.

The guy couldn't read my mind.. Go figure.. My mistake..:-)

They were sent back. Customer service was great though.. No problems at all.. Good guy to deal with..

I'll stick with Nord.. only problem it's in England.. Turns out it's not an issue so far, 5 years now with class ds Hypex NC500, no issues..
Sure like them better than the ICE products.. I have Wyred4sound, too mercy.. Where is the tone control..

Regards
ricevs
1,543 posts
 
There are no such things as "copper resistors"....generally speaking. Both Nord and VTV use metal film resistors. Maybe you think the 3 polystyrene capacitors on the Nord board are "copper resistors"? You are once again mistaken. I wish people were more focused on what they write. Every word has power and meaning. Did you read above what the guy posted about the VTV board versus the Nord Rev D board? He said the VTV board sounded better. I tend to trust what people say when they do listening tests. When they just talk about something and even some of their info is wrong.....well, not a reliable source to believe.
atmasphere's avatar
atmasphere
11,834 posts
 
Take that as I would as colouration distortions, countering what they say earlier in the same sentence as "The NC500 is practically devoid of any sonic signature ”
Actually the two comments sound entirely in agreement with each other.
georgehifi's avatar
georgehifi
10,312 posts
 

As Hypex say, "The NC500 poweramp module is devoid of any sonic signature" this is "without the buffer". And it will give the best "sonic transparency/dynamics" if doable, as I do without any compromises, just better sound and a purer signal path from input to output. 
No additional "house sounding" opamp buffers with colourations/distortions in the signal path.  


audio2design
1,351 posts
 
This is what it says, "Furthermore,the NC500 OEM is an unbuffered amplifier leaving the implementation of an input buffer up to the manufacturer. The NC500 is practically devoid of any sonic signature so this external buffer is a good way of tuning in a “house sound”."

It does not say any of the other things you are implying, and there is no truth that this is true.  We have noted the performance THD+D and IMD is impacted by the output impedance of the buffer when we did testing .... you know on actual test equipment.
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