Purifi Class D

I for one would be very interested in how you rate its SQ ...

Well....first impressions are not good. Restricted dynamics and sound stage. None of the high end resolution and bass control I've experienced with class D in the past. What this tells me is that it simply needs to be burned in. I plugged in my CD player and set it to repeat all. I'll let it go for a day and see how it improves. I hope this amp doesn't need an enormous burin-in period. 

Glad to hear you found a use for your CD Player..

Hi GUTB,

I've noticed your recenht change of approach from condescending & neglecting to personal experience in regard of Class D.
Clap, Clap - RESPECT!!! Thanks for sharing your adventure in the Class D wilderness!

However I am a bit unsure if selecting the cheapest available appearance aside from the evaluation kit does properly suits your usually high quality criteria that you have shown in the past to devaluate Class D ???

I'd be happy if you could elaborate a bit more in detail your approach and explain i.e. whether you selected the unit for its price or its qualities in engineering before, after and around the PuRiFi module???
Which configuration of the module (Mono, Stereo,3x) did you order, and which buffer did you chose with VTV ET-400A ???

Did you prepare your ears and your bias for an uncolored sound experience and what would be your source/signal chain set up for that adventure ? What will be your test tracks ? What will be the reference (system) you compare it to ?

For the record:
In terms of self-oscillating knowledge / research, the AS-forum search would have lead you here .
Scan down to Bruno's response to Sagittarius, where he explains that term.
The Feedback issue is included in that Q&A as well ...

All the best & curious - stay safe & sound
Tom

Okay so....imput impedance. It struck me that perhaps there's an impedance mismatch between my preamp and the VTV. Currently I'm using a Yaqin B-2T, an inexpensive all-tube preamp design. I'm resistant to spending a lot on a pre because I hope one day to get a high-end integrated. This pre has an advertised output impedance of 230 Ohms. So what about the VTV? Their website doesn't say. Searching around google, the figure of 47k Ohms comes up with a few different manufacturers. The Purifi spec sheet states 4.4k Ohms for differential and 2.2k Omhs for SE. Uh....that's insanely low for an amp, is that the right spec? The 47k figures are more in-line with expectations, but is that because of the custom input buffers they use? This thing couldn't possibly be running at 2.2k Ohms, right? I have a Freya which I believe is defective due to what seems like a lot of noise, but it has 75 Ohms on the SE output. 

I sent VTV an email about this. I just considered 230 Ohms good enough for most any amp, but maybe not. That might explain why I was getting such weak performance.

Characteristics are all about the input buffer stage. Which is custom, and can be altered. Have you read this,

https://vtvamplifier.com/frequently-asked-questions/

On 12/12/2020 at 7:53 AM, DuckToller said:

Hi GUTB,

 

I've noticed your recenht change of approach from condescending & neglecting to personal experience in regard of Class D.
Clap, Clap - RESPECT!!! Thanks for sharing your adventure in the Class D wilderness!

However I am a bit unsure if selecting the cheapest available appearance aside from the evaluation kit does properly suits your usually high quality criteria that you have shown in the past to devaluate Class D ???

I'd be happy if you could elaborate a bit more in detail your approach and explain i.e. whether you selected the unit for its price or its qualities in engineering before, after and around the PuRiFi module???
Which configuration of the module (Mono, Stereo,3x) did you order, and which buffer did you chose with VTV ET-400A ???

Did you prepare your ears and your bias for an uncolored sound experience and what would be your source/signal chain set up for that adventure ? What will be your test tracks ? What will be the reference (system) you compare it to ?

For the record:
In terms of self-oscillating knowledge / research, the AS-forum search would have lead you here .
Scan down to Bruno's response to Sagittarius, where he explains that term.
The Feedback issue is included in that Q&A as well ...

All the best & curious - stay safe & sound
Tom

So, my system.

Digital source: custom audio server with i7-7700k all passive cooling no fans anywhere. Paul Pang USB controller + external battery power. SSD power line isolated to another battery. Running Windows 10, Roon, Fidelizer Pro and HQPlayer. AliExpress linear ATX PSU (with separate power rails, not a micro-PSU).

Analog source: Triangle Art Concerto + upgraded platter, TA speed controller, TA Zeus MC, Reed 2A tonearm. Hashimoto SUT (DIY built from eBay). Chinese all-tube clone of some old model of phono stage, I forget which (Marantz?).

DAC: Schiit Yggdrasil Analog 2 (currently).

Preamp: Yaqin B-T2 + NOS tubes and Herbie Rx tube dampers. Schiit Freya as a backup.

Amp: VTV Stereo Purifi with stock input/buffer. Odyssey Stratos (upgraded, currently broken), ODL (early Stratos from a different company that split off from Odyssey years ago). Chinese Naim NAP200 clone. Old Chinese 845 triode amp collecting dust.

Speakers: ProAc D30Rs.

Power: Furutech Rhodium wall outlet feeding amp and isolation transformer. LessLoss level 1 power cable + LessLoss 64X firewall into the amp. AliExpress balanced isolation transformer feeding preamp, DAC, phono stage with Audio Sensability Testament feeding these components from the transformer.

Interconnects: Audio Sensibility Statements and a few other types.

Speaker cables: Audio Sensibility Testaments and matching jumpers. 

21 hours ago, GUTB said:

 

So, my system.

Digital source: custom audio server with i7-7700k all passive cooling no fans anywhere. Paul Pang USB controller + external battery power. SSD power line isolated to another battery. Running Windows 10, Roon, Fidelizer Pro and HQPlayer. AliExpress linear ATX PSU (with separate power rails, not a micro-PSU).

Analog source: Triangle Art Concerto + upgraded platter, TA speed controller, TA Zeus MC, Reed 2A tonearm. Hashimoto SUT (DIY built from eBay). Chinese all-tube clone of some old model of phono stage, I forget which (Marantz?).

DAC: Schiit Yggdrasil Analog 2 (currently).

Preamp: Yaqin B-T2 + NOS tubes and Herbie Rx tube dampers. Schiit Freya as a backup.

Amp: VTV Stereo Purifi with stock input/buffer. Odyssey Stratos (upgraded, currently broken), ODL (early Stratos from a different company that split off from Odyssey years ago). Chinese Naim NAP200 clone. Old Chinese 845 triode amp collecting dust.

Speakers: ProAc D30Rs.

Power: Furutech Rhodium wall outlet feeding amp and isolation transformer. LessLoss level 1 power cable + LessLoss 64X firewall into the amp. AliExpress balanced isolation transformer feeding preamp, DAC, phono stage with Audio Sensability Testament feeding these components from the transformer.

Interconnects: Audio Sensibility Statements and a few other types.

Speaker cables: Audio Sensibility Testaments and matching jumpers. 

Good luck with the VTV. What was your opinion of the "injury roster" Stratos?

Okay so, update on the VTV.

The horrible midrange seems to have mostly solved itself. That's good. There is still a smearing / lack of resolution when things get busy. Midrange sounds -- instruments, voices -- still don't sound really convincing. Another troublesome aspect is that I don't seem particularly interested in long listening sessions. Lack of engagement. This could be a sign of a general lack of euphony which is the kiss of death of anything in my system.

Imaging and soundstage has improved since the early days, but it's still not really convincing. 

Bass however has improved to the point that I'd usually associate with class D. Dynamics have also improved to a level I'd call satisfactory.

Next step I think I'll contact VTV and ask about what changes the input board and buffer options may have. Perhaps a double power supply model will help. If some combination can help midrange I may try that.

These might also be interesting links for ncore and purifi (diy)amps.

https://atm-audio.com/shop/   Scrol down for diy.

https://www.audiophonics.fr/en/power-amplifier-c-6306.html

If we have a run on the now available PuRiFi 1ET-400A designs, I'd vote for either of these solutions:
https://www.apollonaudio.com/apollon-1et400a-mini-stereo-amplifier/

or the monoblocks:

with 2 years guarantee from Apollon Audio in Slowenia. (In my eyes has far better looks than Melania ...)

However, I have decided to wait for the "rumored" PuRiFi designed power supply to arrive before I sign for it.
Cheers, Tom

Quote

there's this one: https://www.marchaudio.net.au/product-page/p451-mono-block-power-amplifier

The March Audio (there's also a stereo version) looks very well made, and appears to have a nicer (more substantial) case.

A different Class D, but this new amp from Boenicke looks promising (Sven would never sell it otherwise):

 https://boenicke-audio.ch/products/electronics/p1/

https://6moons.com/audioreview_articles/boenicke9/

1 hour ago, Blake said:

A different Class D, but this new amp from Boenicke looks promising (Sven would never sell it otherwise):

 

 https://boenicke-audio.ch/products/electronics/p1/

 

https://6moons.com/audioreview_articles/boenicke9/

 

That does seem like a very unique amp. Several high-end tweaks built-in like direct-soldered AC cable, Baybee filters, LessLoss firewalls, etc.

Another interesting finding. I decided to swap out my reference power delivery to the amp: LessLoss level 1 power filtering cable + Firewall 64x from a Furutech GTX-D(r) NCF outlet to a standard black 14-guage power chord from a standard outlet. The difference on one test track was...almost nothing. Maybe the it was a touch muted / muffled on the standard cable, but nothing you couldn't chalk up to audio memory effects. This hasn't been my experience with my linear amps. I wonder if the switching power supply is just agnostic to mains quality -- or it's already so messed up the mains quality won't make a difference?

15 minutes ago, GUTB said:

Another interesting finding. I decided to swap out my reference power delivery to the amp: LessLoss level 1 power filtering cable + Firewall 64x from a Furutech GTX-D(r) NCF outlet to a standard black 14-guage power chord from a standard outlet. The difference on one test track was...almost nothing. Maybe the it was a touch muted / muffled on the standard cable, but nothing you couldn't chalk up to audio memory effects. This hasn't been my experience with my linear amps. I wonder if the switching power supply is just agnostic to mains quality -- or it's already so messed up the mains quality won't make a difference?

It's been my experience that the quality of the mains supply becomes more and more important, the closer one is to optimal sound. And that there is no such thing as a "reference power delivery" - the interplay between what the mains is delivering and how the audio component reacts to that is too complex for there to be a simple answer that "solves everything" - in the decades that I've been doing this, I have not yet found a plug 'n' play solution.

Which a long-winded way of saying, in your situation I would experiment, experiment, experiment - in all sorts of ways, to try and get a handle on what matters ...

3 hours ago, fas42 said:

 

It's been my experience that the quality of the mains supply becomes more and more important, the closer one is to optimal sound. And that there is no such thing as a "reference power delivery" - the interplay between what the mains is delivering and how the audio component reacts to that is too complex for there to be a simple answer that "solves everything" - in the decades that I've been doing this, I have not yet found a plug 'n' play solution.

 

Which a long-winded way of saying, in your situation I would experiment, experiment, experiment - in all sorts of ways, to try and get a handle on what matters ...

Interesting information, thank you. I'm bringing in yet another Odyssey amp. this one a used Kismet (top of the line). It'll be interesting to see how that responds and compares with the VTV Purifi.

I wouldn’t be surprised if this one sound better or equal. 
AT522NC Stereo Amplifier (200W RMS per channel) $2,195.00

https://www.ati-amp.com/AT54XNC.php

Just giving you guys an update. I haven't run the VTV for several days now since I got in my "new" Odyssey Kistmet bought used for $1500, it's just 3 years old. No need for burn-in which is a bonus. Frankly...the VTV doesn't stand a chance. I'll do a final, formal comparison before officially declaring it a loser but there a few things I'd like to try first, namely my newly functional CD transport which has shown a huge improvement over my normal digital system. Want to make sure I'm giving things a fair shake. It's just that when music enjoyment comes back immediately after bring in a linear amp it tells me that the fundamental flaw of class D remains unsolved. But we'll see. There is a lack of mid-range quality, an unconvincing nature to it -- missing necessary harmonics or some kind of ugly distortion artifact I can't really say. It struck me especially when listening to the Kurt Elling album Upward Spiral, in parts where the sax player tries to match Elling's baritone and the result is ugly and jarring.

Is it this midrange issue what's causing a lack of engagement and enjoyment? I can't really say. Again there's a few things I need to try before making a final judgment.

23 minutes ago, GUTB said:

Just giving you guys an update. I haven't run the VTV for several days now since I got in my "new" Odyssey Kistmet bought used for $1500, it's just 3 years old. No need for burn-in which is a bonus. Frankly...the VTV doesn't stand a chance. I'll do a final, formal comparison before officially declaring it a loser but there a few things I'd like to try first, namely my newly functional CD transport which has shown a huge improvement over my normal digital system. Want to make sure I'm giving things a fair shake. It's just that when music enjoyment comes back immediately after bring in a linear amp it tells me that the fundamental flaw of class D remains unsolved. But we'll see. There is a lack of mid-range quality, an unconvincing nature to it -- missing necessary harmonics or some kind of ugly distortion artifact I can't really say. It struck me especially when listening to the Kurt Elling album Upward Spiral, in parts where the sax player tries to match Elling's baritone and the result is ugly and jarring.

 

Is it this midrange issue what's causing a lack of engagement and enjoyment? I can't really say. Again there's a few things I need to try before making a final judgment.

What kind of input opamp are you using? Experiment, they even have a tube buffer.

Have read that the stock input buffer is a weak link, on the VTV and other builders like Nord or Apollon, which offer several upgrade options.  Additionally, the VTV is value oriented versus some of the other builders that have spent more efforts on layout, wiring choices, parts upgrades, and power supply enhancements.  

This one even uses what appears to be LPS (3 toroids) to drive input and output of amp, if I understand this correctly ($10K, hardly a bargain):  

https://www.stereophile.com/content/lkv-veros-pwr-power-amplifier

Run Aerial 10Ts, which are power/current hungry beast, and sent a note to Purifi to see if they intended to produce a double power amp, like 400 watts into 8 ohms, which had been rumored.  Response was no, just a rumor.  Bridged monos, they said wouldn't help with these speakers, as power goes up but current capabilities wouldn't increase in that configuration.  Sticking with the McCormack DNA-500, even checked on SMc upgrades described here in CA, though $5K cost, which is more than I paid for the amp.

I wondering about transformer based class-d amps. So not only for the input stages but also for power. Is somebody doing that? 600va transformer, rectifier and big capacitance. 

And the question would be if that would be better then the smps?

1 hour ago, RickyV said:

I wondering about transformer based class-d amps. So not only for the input stages but also for power. Is somebody doing that? 600va transformer, rectifier and big capacitance. 

And the question would be if that would be better then the smps?

 

That's what the LKV one I linked above utilizes, the reviewer was smitten.  Can't be a big magazine advertiser based upon the size of the company.  Here is what the pointed out on its site:

Transformers: Three separate toroidal power transformers are employed in the PWR+: (a) One large 1KV transformer weighing over 12 pounds supplies high current for the Class D output stage. (b) A second serves as a floating, +15 volt supply for the driver circuitry in the Purifi module. (c) A third feeds the power supply for the LKV Class A input/gain/driver stages.

High Current Supply: This power supply employs almost 40KuF of capacitance and is specifically designed to meet the demands imposed by Class D amplification circuits. Most importantly, it copes quite effectively with “power pumping,” a problem unique to Class D amps.

Line Level Supply: To assure the very accurate, low noise/distortion performance for which the LKV Class A circuits are known, each power rail in this supply has two stages of power regulation, a capacitance multiplier, and 40KuF of capacitance.

3 hours ago, RickyV said:

I wondering about transformer based class-d amps. So not only for the input stages but also for power. Is somebody doing that? 600va transformer, rectifier and big capacitance. 

And the question would be if that would be better then the smps?

 

Which immediately reminded of muralman1, on whatsbestforum. He used personally tweaked versions of these, https://6moons.com/audioreviews/h2o/m250.html, to drive Apogee Scintillas. Which are known for having "impossible", amp killing impedances. But it was worth it for him, because the setup delivered, convincing sound.

Unfortunately, he is no longer with us - but I enjoyed engaging with him; he was one of the very, very few people who understood what audio reproduction is capable of.