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
mspot
115 posts
 
So how bad IS the standard Purifi in the VTV? Will the upgraded input board and discrete opamps move it to another level?
In my experience, yes upgrading the input board changed the VTV Purifi amp from unacceptable to acceptable. Others have reported a similar experience:  https://www.audioasylum.com/cgi/t.mpl?f=amp&m=238411

My thought is the following. At $979, the VTV Purifi with Hypex buffers is by far the lowest price Purifi stereo amp on the market. Everybody else is selling Purifi stereo amps in the range of $1400 and above, and only with custom buffers. Presumably nobody else wants to offer the Hypex buffer because it is a poor match for Purifi. If you upgrade the VTV with custom buffers, then the price jumps up to $1400 and more, making it similar to the rest of the market. So the $979 price is only there to attract attention and bargain hunters, even if the Hypex board doesn't work well with Purifi.
madavid0 OP
214 posts
 
It's a little surprising that Purifi would release a compromised product to the public to represent their brand. I guess I'll look into a input upgrade then. It's just there's no way anyone with any kind of good amp experience would think this is fine, forget about great.
jaytor's avatar
jaytor
765 posts
 
To be fair, Purifi does not sell their module with this input buffer. In fact, they don't sell their products to the public at all except to the DIY community. The amp you bought includes a buffer that wasn't even designed with the Purifi module in mind. 

Purifi expects that their OEM customers will add value to their module by designing proprietary power supplies, input buffers, and other logic and circuitry. The NAD M33 or the LKV Veros are more the kind of products they envision, or at least the VTV with their tube input buffer.

Amplifiers built with the Purifi module are only going to be as good as the sum of its parts, like any other electronic product. If you build the amp with an entry-level power supply and the cheapest possible input buffer, it's not going to be an good indicator of what the module is capable of. 

fstein's avatar
fstein
199 posts
 
You have the wrong buffer. Call Warren and talk.
ricevs
1,543 posts
 
Yes, to echo the above. The input board you have in your VTV is the Hypex eval board that was originally for the NC500 module. Purifi has also made an input buffer board (both stereo and mono) that uses different regulators, op amps, etc. Warren at VTV is now going to sell those, as well. However, the Purifi one won’t sound as good as the VTV custom input board with discrete op amps......but, of course, there is lots of other things you can do to improve the sound. What you have is the least good sounding Purifi version that anyone can buy.

What you have:
https://www.hypex.nl/product/nc500-evaluation-board/51

What Purifi offers and now VTV sells now too. Check out Eval 1 and 2:
https://purifi-audio.com/vare-kategori/transducers/

What VTV sells as an upgrade that is better than the above the two:
https://vtvamplifier.com/product/vtv-amplifier-custom-input-buffer-hypex-nc500-nc1200-nc2k-purifi/

Even a dual mono VTV with the VTV custom input buffer boards using the best buffers will not give the best sound.  There is much more to be gotten from tweaking everywhere.  You cannot do this at this price point.   It is all plug and play at the $1500/$2000 level.


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