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
No, you are reading the spec of the amp without a buffer. The stock Hypex generic buffer board that is sold by VTV has 47K to ground on each phase. This is in the buffer added mode. If you configure the board so the buffer is not in the circuit.....then you would have 14db less gain and have the 2.2K input impedance. I am pretty dang sure VTV supplies the input board configured with the on board buffer.....so the input impedance is 47K. Please contact VTV for more info. Why would you ask anyone else? I never understand why people ask on Audiogon about things before contacting the manufacturer.

I mod the crap out of VTV Purifi based amps. Sounds nothing like stock. All stock modules by all manufacturers need heavy mods to sound great. The implementation of every single thing makes a sonic difference....fuses, jacks, wires, input stages, shortening the signal path, bypass caps, mods to input stages and regulators, changing output coils to air core, etc, etc. etc. There are so many levels of sound that can be achieved. BTW.....the stock Hypex buffer using 4562 op amps and ordinary regulators is nothing like having the custom input board using Sparko labs regulators and Sparko or better input op amp.....but that board needs a lot of mods as well. I modifiy the Sparko labs regulators, the Sparko labs op amps (seriously better with mods), change all the parts in the input circuit to better ones, use better bypass caps on the output of the regulators, hardwire much better input wire directly to the input stage bypassing the connector on the board, hardwire the output of the input buffer directly to the Purifi modules bypassing the edge connector, etc. etc. etc. The sum of all my mods is a completely different amp.....All implementations of Purifi modules will sound completely different. You really need to get that the input buffer and implementation is just one thing. There are tons of ways to make the sound better.....including modding the input buffer itself. The generic stock sound of the stock Purifi module is just that....a generic sound.......there is so much more to experience.

Shortly, I will have a fully modded amp that I will be sending out on tour.....then you can try without buying......then you will know what is possible with Purifi......stay tuned.

By the way, the standard input buffer sold by VTV for use in their amps is from Hypex....not Purifi. You have to buy the Purifi input board directly from Purifi.....and it is not a mono module. It is a stereo module and uses different op amps and different regulators than the stock generic Hypex boards sold by VTV.
Thank you for the information. I actually had a Freya lying around that has 75 Ohms on the SE output. I tried it out and I really didn’t notice a difference...noisy, more blurred, but that’s the Freya’s fault. In terms of dynamics I didn’t really notice any difference.

So how long does it take for burning in?

It’s plugged in to a Furutech outlet using a LessLoss level 1 cable (the older version, not the C-Marc) and LessLoss firewall. Pre and DAC are on the same outlet going through a balanced isolation transformer from AliExpress. There shouldn’t be any current-limiting effects going on. The Stratos doesn’t have this problem.

I actually have two Stratos amps. The first is an upgraded Stratos with the extra caps. The second is an early model back when they were ODL. Same circuit but the newer one has an encapsulated toroidal, custom Odyssey caps and different PCB and I think different wires. I broke it and have been trying to fix it, so far without much luck. While I was trying to fix it I got the used ODL as a filler. Frankly, the ODL sounds significantly worse -- not terrible, but definitely a step down from the newer / upgraded Stratos. After day 1 of the VTV, it actually sounds a lot like the ODL, except more congested. That is surprising to me. If nothing else I would have expected super high class D damping power to have an obvious effect. The higher current should have had a more obvious effect...unless real-world current delivery under load isn’t good. I do understand that it needs to burn in, but this result is different compared my expectations built from experiences with other class D. It certainly sounds like trash compared to a NC1200-based amp I heard at AXPONA(?) a few years back.
There is nothing as simple as you state.  I can make the amp you have jump at you like lightning.  Even the AC filter on the VTV is limiting the current and transparency.  It is only rated at 10amps.....the fuse in the power supply is 12 amps......limitations.  The power switch kills the sound.  I mount a cryoed demagnetized Furutech inlet and hardwire super wire directlly to the power supply pins.....with audiophile fuse in between and remove the stock fuse on the switching supply......Just with these mods you will hear more dynamics and slam and transparency throughout the spectrum.  Any single thing can limit the sound.

I can make the amp you have jump at you like lightning.
Even the AC filter on the VTV is limiting the current ??
The power switch kills the sound. ??
the fuse in the power supply is 12 amps??  
I mount a cryoed demagnetized Furutech inlet??  
with audiophile fuse in between ??


This is sounding like snake oil to me.