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?
Using King Crimson's track to make a final evaluation ? Ridiculous. A very processed recording. Try the works of Tony Minasian. Reference quality demo material, for sure, then, make up your mind.
I didn't use the King Crimson as the final arbiter, it's just that when I heard the VTV blur the chime percussions into a mess I got angry and decided I was done. I'll look into this Tony Minasian.

But, once again, I've been talked into trying something. I ordered a pair of input boards from VTV with Sparkos opamps. I do appreciate the speed of VTV's responses. If the defeault Hypex board is really that compromised I thought I should give it a fair shake in a configuration which is it supposed to use. I don't get why Purifi thought this thing sounded good enough to release to the public but...oh well. They're coming.
If the defeault Hypex board is really that compromised
I’ve got those those Hypex buffer boards in my NC500 mono’s that have my own big linear supplies, there’s nothing wrong with the buffers (they don’t sound bad as some here would like you to believe) Your problem is elsewhere.

Saying that, my MSB discrete R2R dac has got volume control in the digital domain with up to 5v out balanced, and by-passing the Hypex buffers altogether and going direct from the MSB's balanced output into the balanced input of the NC500 modules, the sound took on a massive improvement in transparency/dynamics and slam.

(Moral of the story: Less is more, just like I always say with passive pre’s vs active pre’s also when possible)

Cheers George
"I don't get why Purifi thought this thing sounded good enough to release to the public"  What are you talking about?  You are not hearing a Purifi.....you are hearing a Purifi with a Hypex buffer put together by VTV.....The Purifi can use any buffer on its input.........a stock Hypex buffer board, a Purifi buffer board....a VTV buffer board with various different sounding discrete op amps....and then are mods to the input boards, mods to the input stages, mods to the Power supply, AC inlets, etc. etc......You really don' t seem to have any idea of what you are talking about.   
a stock Hypex buffer board
There is nothing wrong with that buffer, Putzy's not an idiot to release a Hypex product that kind of bad sound ****
You say there is nothing wrong with it and at the same time you say there is a "massive improvement"  when you bypass it.  You cannot have it both ways.  Every op amp....every regulator......every everything....has a sound.  So all buffers, etc will sound different.  Some will sound bad, some are OK, some are good, some are really good, some are great.  If you bypass it and you get a massive improvement.....then certainly, it is not great.

Wake up!! Did you come down with the last shower?

It doesn’t sound ****, like your making out.
And of course, leave out any buffer regardless of how good if one can with high output source, and you’ll reap those benefits of extra transparency/dynamics and slam, by going direct into the Class-D module with no buffer at all in the way.

And that Hypex buffer is a perfect match with the Purifi module, that’s why it’s called and marketed as a buffer.

It something else the OP is hearing, and you know what that leaves, the Purifi module itself!
And that Hypex buffer is a perfect match with the Purifi module
Have you heard them in combination? I have, and I found them not a good match together. Others feel the same way, for example https://www.audioasylum.com/cgi/t.mpl?f=amp&m=238411. VTV seems to be the only vendor offering this combination. I think there's a reason why nobody else is doing it.
Have you heard them in combination? I have, and I found them not a good match together.

Are you saying it sound like **** like ricevs, and it’s a bad design bad sounding buffer?

Or the impedance match is no good as a buffer? then any buffer will have the same problem.

Do you think Putzey made a bad one on purpose?

Because it is a "simple buffer", made by someone who could make one in his sleep, using good sounding opamps, which is hard to get wrong.
He could teach just about anyone how to make one in 15 mins, even adjusting the gain of it
Here is one using the opa1632 opamp https://ibb.co/njDHP1H Pin 6 is a misprint, should be 5. Pins 3 and 6 are then for + and - from the powersupply.

No, like I said there’s something else the OP is hearing, and all that’s left is the Purifi itself.

Cheers George
The power supply has at least as much influence on the sound as does the input buffer, so "all that is left" is not just the Purifi module.

Further, the Hypex input buffer was never intended as a finished product. It is about as simple a circuit as can be used to provide impedance matching and gain. While the op amps used (LM4562) are decent, they are designed to be operated at a higher voltage than is used on the Hypex buffer to get optimal performance. The 7812/7912 voltage regulators used on this board are decades old and far from state-of-the-art when it comes to noise and response speed, so there is a lot of room for improvement. And there is no frequency limiting and EMI/RFI filtering circuits, so there is lots of opportunity for environmental electrical noise to cause problems. 

And, of course, there are improvements that can be had from wiring, connectors, layout, etc, but these will likely be more subtle compared to the power supply and input buffer design.

Bottom line, this amp as currently built is about the worst case scenario for the Purifi module. You can only go up from here. 

Wow you need to look at the LM4562 a bit better than what your waffling on about.
Texas Instruments designed it to work it’s optimum between 5-17v, and from what i can find it works with +-12v with the Purifi
+-12v gives .00004thd +-17v gives .00003thd sweet      all in it.https://www.ti.com/lit/ds/symlink/lm4562.pdf?ts=1609274706414&ref_url=https%253A%252F%252Fwww.ti...
Using King Crimson's track to make a final evaluation ? Ridiculous.
Formantera Lady, from King Crimson's Islands LP; very nicely recorded. I play it at audio shows quite often as it can really show off a system!
To the OP:
Calling PuriFi "junk" because you don’t like something you bought that has PuriFi modules in it makes no sense. I bought some iced tea that tasted bad. Does that mean tea is junk? Water is junk?

You don’t like the amps you bought, understood. Please leave it at that. You now have a problem to solve, whether it’s with the amps you bought, with the vendor, with something else in your system, or just with system synergy. No use slinging mud -- it won’t help solve it.

I'm one of the few people online who actually tries things and reports my findings accurately. I do understand that most don't actually want to read critical information about a product, they just want to have their bias confirmed. I've learned that what I do is not really welcome on the Internet and so I've been banned from most forums, most recently ASR which in particular is a vile, toxic cult.
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.
@djones I'd definitely be willing to do a blind test, but understand that's a pretty tall order when we're talking about comparing amps. In reality your requirement for blind testing is just a roadblock to protect egos and confirm biases. Listening impressions are fake and the correct method of conducting them are too difficult to achieve in everyday life, so you can remain comfortable in willful ignorance.

For example, in my ASR thread about Purifi, I noted that my reference mains cable chain had no effect. Responders agreed with this finding. Strange, shouldn't this sighted, unscientific listening impression also be invalid? How do I know there isn't an difference between mains cables? Maybe the lack of difference is just in my head, ie, I expected to change so I heard none? Funny. Weird. How does the requirement for blind testing disappear when the results conform with negative expectations? Of course because the responders just want to have their biases confirmed, the requirement for blind testing, ABX, etc, is just a tool to support the bias.
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. 
I've been told by experienced audiophiles here and elsewhere that the default Hypex board is junk, so in order to give it a fair shake I ordered a set of custom ones from VTV. I think it's pretty obvious I'm not doing this just to make you feel bad about your support of class D / Purifi. I got the cheapest base unit to begin with because I figured there wouldn't be a substantial difference and at least I'd get a baseline grasp of the sound. I'm told that's not the case and the default configuration is compromised. Listening to the awful midrange I can see that there MAY be truth to that statement. Also it might be just that the artifacts are most noticeable in the midrange and that it's impacting the whole audio band. If these custom boards and opamps fix the issue and elevates the sound, I will faithfully report it. If it doesn't, then back it goes.
I’ve been told by experienced audiophiles here and elsewhere that the default Hypex board is junk
Any one that says that is junk themselves and needs to be committed.
I’ve shown what the Hypex board is, it’s opamps may not be the "absolute very best" of opamps, but they’re not far off it. Anyone that can hold a soldering-iron can build one. And you’d have to be an absolute idiot to stuff up a buffer design using them. And I doubt Putzey is one.

Cheers George
I've been told by experienced audiophiles here and elsewhere that the default Hypex board is junk
You  also need to ask them about their last hearing test just so you have a proper baseline. There are some pretty good class D out there.

My Peachtree Nova 150, while not as good as my current gear (BM AHB2), was a very good Class D integrated. I now wish I did not sell it since I need an integrated today that will sound good with KEF LS50's and can also tolerate some toddler abuse.

The Purifi Class D is what I am likely going to get for this new requirement but it will cost me more than the Peachtree.
If I report that the Purifi is, in fact, junk -- for midrange problems or just as overall lack of engagement (the real reason why you sold the Peachtree probably) would that influence your decision? My guess is -- almost certainly not. In my experience people just want to have their bias confirmed. If it's just one or two voices critical about the product, it doesn't matter if they're the honest ones with the discernment that should be listened to and not the masses of the echo-chamber who can only compare it with other bad-sounding gear. What matters is that the echo chamber tells you want you want to hear.
I think it is perfectly reasonable to report that you weren't happy with the particular VTV model you have, but to lump all products that use the Purifi module in the same bucket is pretty rediculous. I haven't personally heard any products that use the Purifi module yet, but I know from my limited experience listening to products that use other class D modules that there is a lot of differences in the way these amps sound depending on how they are designed and built. 
Same can be said for Hypex modules. Many designers incorporate them in many different ways with excellent results.
I have listened quite carefully to a pair of monoblocks made by Apollon Audio using the PuriFi modules. In my system, in my room, with my own source material, I consider them in the same league as the well-respected Class AB amp I normally use -- I might wind up liking them better. As a frame of reference, the AB amp has an MSRP more than twice what I paid for the monoblocks, delivered. (I don’t intend a value comparison -- there are reasons for the cost differential, at least some of which involve value added, such as dealer support, longer warranty, and so on. Just to say it’s not a low-cost item.)
Oh -- I don't think either the AB or the PuriFi amps are "junk."
Well, I installed the VTV input boards and Sparkos opamps today. I won’t post immediate findings because those are always defunct within a day or two so I’ll let it burn in for the time being.
I got the VTV with their buffer. I tried all of the op amps, (each requiring at least 36-50 hrs break-in with noticeable changes), and the Weiss, which is from their $25k Medeus DAC, absolutely blew everything out of the water. Pure transparency. Only then do you hear what the Purifi is capable of...completely on another level of musicality, sweetness, transparency. Completely smoked the Sparkos and Sonic Imagery.

Granted, I also upgraded all internal cabling to Furutech DSS and added their pure copper posts and inlets. Phenomenal once you get through a few hundred hours of burn in.. I played for a friend that has a whole setup of Tron amps (do the $ math) and $10k+ in power conditioning, with the same Furutech cables I have, and he was blown away. The Purifi module really does accomplish what Bruno set out to do, which is give you the best of tubes without the artifacts (that some like for hi-fi listening). I use this in my studio.

And yes, the amp out of the box sounded like complete garbage, worse than a portable bluetooth speaker. Needs real burn in to get there. And the buffer board exists for a reason..email Daniel Weiss for more info. ;)

@clustrocasual That's very interesting. If the Weiss is that good perhaps I'll hold off on returning it. How did you replace the cabling? Including the Molex connector cables?
I did not replace the Molex from the hypex power unit to the amp module, but its on my list. I would have to source the right cabling for this.

I did remove the Molex that connects to the IEC inlet and soldered the DPS directly to that board. I used the Furutech pure-copper connector clips for all other points, and soldered the interconnect from the XLR inlet to the board.

I plan to do a write up with pictures once I'm done with some final testing in a couple weeks. I did each part one at a time so I could hear differences, and with Furutech's notorious 300hr burn in, its taken me a few months. I don't change anything unless I hear a clear improvement. 

But the first thing I did was test the op-amps with basic OFC cabling and the Weiss really opened my eyes. (or is it the Purifi opened my eyes because the Weiss is transparent?).
If they are using the OEM Hypex boards as input boards it is crap. It is VTV’s fault.
???????  What are you talking about?  You can buy from VTV several different input boards......the Hypex OEM, the Purifi board, the custom VTV input board that allows all kinds of different op amps to be tried and also a custom VTV tube input board that also allows different op amps.
I had a pair of Nord Hypex NC500 monoblocks a couple years ago and was kind of disappointed with the sound  quality. These amps came with input buffer boards that supported the Sparkos and Sonic Imagery discrete op amps, and I tried them both. I preferred the warmer, smoother sound of the Sparkos in the system I had then, but not by much. The Sonic Imagery opamps offered noticeably more detail, but were more sterile sounding.

These amps replaced a Krell FPB-300 which had died for the second time and I decided it was time to sell it for parts (which I now kind of regret), and they really weren't a good substitute. Granted they cost WAY less and were a lot easier to deal with (both weight and power consumption) but they didn't work for me. 

I ended up selling them and replacing them with a Parasound JC-5 which I was much happier with. That was close to 2 years ago. I have since completely changed my system (although I still have the JC5) and have really gotten into DIY. After building a pair of FirstWatt F5 turbo monoblocks and a pair of Neurochrome chip-amp monoblocks, I decided to give class D another try. 

I recently completed a pair of Purifi-based monoblocks. But instead of using the typical Hypex SMPS, I built them with a large linear power supply, similar to what you'd expect to find in a high-end class AB amp (1500VA shielded transformer with ~200,000uF of Nichicon filter caps). As a first round, I decided to use the Neurochrome input buffers which are a well-engineered op-amp design.

I plan to experiment with other designs including discrete op-amps and fully discrete in the future, but with this relatively simple and cost effective buffer, these amps sound quite nice. I'm sure there is some "pride of my own build" bias  influencing my perspective, but I have to say that I was not that impressed with my FirstWatt F5 Turbo build. The Purifi amps are better in just about every way (more dynamic, much more detail, quieter background, sweeter midrange, better soundstage, WAY less heat). 

You can see a couple of photos on my system page. https://systems.audiogon.com/systems/8726

I'm thinking about trying an input buffer using the Weiss OP2-BP op amps next. I've heard good things about them, and it would be interested to compare them to a high quality conventional op-amp implementation. 
@jaytor -- You have a wonderful touch with the DIY projects. If I had the skill and patience to make things so neat and beautifully laid out, I’d be a DIYer myself.

As someone interested in those PuriFi modules, I’ll be very interested in how you like the Weiss op amps. Please do post and let us know.

I believe the Weiss are not plug-compatible with the Sparkos and Sonic Imagery units. Is that right?
Thanks Mike. I believe the Weiss opamp is pin compatible with the Pro series opamps from Sparkos and Sonic Imagery, but not their dual discrete opamps. 
I want to give my amps a couple more weeks of burnin before I decide how to proceed with the Weiss opamps. 
What an entertaining thread. A bunch of people (mainly) with obviously from this thread and others weak engineering skills (at best) with odd exception pumping their chests and egos while arguing about things they poorly understand while making wild and patently false claims about all kinds of things.

w.r.t. the purifi and hypex modules they need an input buffer to operate to specification. They cannot just be driven with a "lowish" impedance source.  They are meant to be driven with a very low impedance source, i.e. like the buffer circuit on the eval boards.  It sounds like the ops supplier is not qualified at what they are supplying.
VTV supplies the amps with various input buffers.....all of which drive the Purifi module with super low impedance. However, they all sound different.  Yesterday, I A/Bed the Weiss op amps versus my custom modified Sparko Labs 2590 op amps......different but in the same league.  Stock, the Sparko is not in the same league at all as the Weiss.  Everything you do makes a difference.  A complex game this is.
My videos about VTV have been popular. Also check out my Roon - 10 things you don't know video.

VTV Purifi Amplifier - Input Buffer Upgrade Video
Have to formed an opinion about the sound of the vtv amp with the baby sparko op amp versus the Hypex board and have you listened to other discrete op amps and compared sonically with the baby sparko?  I think a lot of people would like to know what all these options do to the sonics.  Do we get more by paying more?
I assume these various opamps are being compared sighted, I doubt in a blind test anyone could tell one from another. 
djones51"I assume these various opamps are being compared sighted, I doubt in a blind test anyone could tell one from another."

Perhaps you should test you're theory by actually conducting proper, appropriate, repeatable blind tests but I suggest and recommend that you engage other listeners in the test because I do not think you will hear a difference because of your "expectation bias" that you won't but it would be an interesting exercise for you undertake to determine, establish, and substantiate you're claam.
My theory has already been tested, none could tell a difference. Better luck next time.

How did you guys do the blind test with the VTV amps? Did you have one Purifi amp with 4 or 5 opamps to switch out or did you have 4 or 5 Purifi amps with a different opamp?

My theory has already been tested, none could tell a difference. Better luck next time."

My English suffices for me to detect this an an insult, which is the type of response we could expect from someone who makes a broad, sweeping, over "arching" claim for which he has no proof, substantiation or references and which reflects an underlying inability to comprehend or understand the actual topic under discussion so as you say "Better luck next time" if you want to be accepted as an authority or expert.
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 - 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. 

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. 
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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