Purifi Class D

[GUTB]

I thought the LKV was a custom GaNFET design. Is it a Purifi? I put the VTV back in, currently playing CDs.

 

Dynamics are acceptable, although weak compared to either of my Odyssey amps, and definitely the D-Sonics (Pascal) I tried in the past. It's probably very much a current delivery limitation. Possibly the dual power supply configuration would help with that. However that's something that you should be able to solve. What I'm looking for is if the sound of class D is now good enough to be an alternative to linear circuits. The answer I've always arrived to up to now is "No", and people who say otherwise I suspect simply don't know what good sound is or they're being wow'd by some technical aspect but failing to identify why their system is so boring and uninvolving.

[RickyV]

27 minutes ago, GUTB said:

I thought the LKV was a custom GaNFET design. Is it a Purifi? I put the VTV back in, currently playing CDs.

 

Dynamics are acceptable, although weak compared to either of my Odyssey amps, and definitely the D-Sonics (Pascal) I tried in the past. It's probably very much a current delivery limitation. Possibly the dual power supply configuration would help with that. However that's something that you should be able to solve. What I'm looking for is if the sound of class D is now good enough to be an alternative to linear circuits. The answer I've always arrived to up to now is "No", and people who say otherwise I suspect simply don't know what good sound is or they're being wow'd by some technical aspect but failing to identify why their system is so boring and uninvolving.

I know https://orchardaudio.com/shop uses GaN fets.
And https://agdproduction.com for non diy audio. Not sure if GaN fets would help in the un involving department.

[fas42]

41 minutes ago, GUTB said:

 

Dynamics are acceptable, although weak compared to either of my Odyssey amps, and definitely the D-Sonics (Pascal) I tried in the past. It's probably very much a current delivery limitation. Possibly the dual power supply configuration would help with that. However that's something that you should be able to solve. What I'm looking for is if the sound of class D is now good enough to be an alternative to linear circuits. The answer I've always arrived to up to now is "No", and people who say otherwise I suspect simply don't know what good sound is or they're being wow'd by some technical aspect but failing to identify why their system is so boring and uninvolving.

 

"Boring and uninvolving" can be as simple as a static buildup issue - interesting timing here, because I had this turn up yesterday, as a problem. Went through everything, couldn't find a cause - and as always should be done, looked very carefully at the last bit of tweaking ... this was a very long bit of cabling added, which was only casually organised to prevent wrong contact between materials - and lo and behold, the assembly had been bumped and disturbed enough for the cabling to slip out of position, and touch what it was not meant to.

[RickyV]

58 minutes ago, GUTB said:

I thought the LKV was a custom GaNFET design. Is it a Purifi? I put the VTV back in, currently playing CDs.

 

Dynamics are acceptable, although weak compared to either of my Odyssey amps, and definitely the D-Sonics (Pascal) I tried in the past. It's probably very much a current delivery limitation. Possibly the dual power supply configuration would help with that. However that's something that you should be able to solve. What I'm looking for is if the sound of class D is now good enough to be an alternative to linear circuits. The answer I've always arrived to up to now is "No", and people who say otherwise I suspect simply don't know what good sound is or they're being wow'd by some technical aspect but failing to identify why their system is so boring and uninvolving.

 

would this help with liveliness and un-boringness??

 

 

[GUTB]

1 hour ago, fas42 said:

 

"Boring and uninvolving" can be as simple as a static buildup issue - interesting timing here, because I had this turn up yesterday, as a problem. Went through everything, couldn't find a cause - and as always should be done, looked very carefully at the last bit of tweaking ... this was a very long bit of cabling added, which was only casually organised to prevent wrong contact between materials - and lo and behold, the assembly had been bumped and disturbed enough for the cabling to slip out of position, and touch what it was not meant to.

 

Interesting. I do need to get back there to make sure cables aren't touching things they shouldn't...I set that up, but changing things  around frequently and it inevitably gets messed up. I also moved my audio PC up to front rack so that I can use a shorter USB cable. Also I now have a CD player sandwiched between 2 amps, I'm sure that's not optimal. Got to sort all that out. I'm really trying to give things a fair shake.

[sandyk]

3 hours ago, GUTB said:

The answer I've always arrived to up to now is "No", and people who say otherwise I suspect simply don't know what good sound is or they're being wow'd by some technical aspect but failing to identify why their system is so boring and uninvolving.

Do you have any performance graphs and measurements for this amplifier ?  

[GUTB]

2 hours ago, RickyV said:

 

would this help with liveliness and un-boringness??

 

 

 

Possibly. I emailed the VTV guy about my findings and various options which might help. He did mention the tube board greatly increases the sense of holographics. The various opamps are supposedly more about tonal quality which MAY in fact help the problematic midrange. He mentioned that someone is doing an extensive comparison of opamps in this amp in a positive feedback article soon, I should go check that. Also it's a little concerning that Purifi can't come with a decent input circuit -- if all this is to be believed. Someone on audiogon told me the standard amp is just a toy and it really needs at least upgraded boards and opamps.

[barrows]

Actually, Purifi’s own standard input boards (Eval 1 & Eval 2) sound great with the Purifi modules, but these are much different than the Hypex input board.  In my DIY Purifi amp I am running the Eval 1, powered by a custom linear power supply of my own design, and the sound quality is fantastic.

The standard Hypex demo input board is just not really suitable for final products (and was never meant for such).

[barrows]

To add to my above comment:  The VTV standard Purifi amplifier build uses the Hypex demo input board.  This input stage is flawed in at least two ways:

 

1.  It has no input filtering for RFI.  All amplifiers should have RFI filtering on their inputs, and this is especially important for class D amplifiers, where RF getting into the inputs can cause serious, audible, consequences.

2.  It uses ancient, 78xx and 79xx voltage regulators with very poor noise performance and high frequency noise rejection ratios.  The opamp used in the input stage is a high speed precision audio opamp, which requires a very good low noise power supply to perform its best.

 

In comparison, the Purifi Eval 1 and 2 input boards have the appropriate RFI filter circuits at their inputs, and they have onboard very sophisticated discrete voltage regulators designed specifically to provide ultra clean low noise power to the input stage opamps.  These discrete regulators also feature very high power supply rejection at high frequencies, which is critical for a class D amplifier running on SMPS to keep high frequency noise out of the opamps.

 

It is an entirely unfair to evaluate the performance of the Purifi modules based on using them with the Hypex demo input board, and this is why VTV, and other amp builders, offer more sophisticated input board options, with proper input filtering and discrete voltage regulation.

[57gold]

 

17 hours ago, GUTB said:

I thought the LKV was a custom GaNFET design. Is it a Purifi? I put the VTV back in, currently playing CDs.

 

 

 

"LKV Research founder Bill Hutchins uses Purifi Audio's 1ET400A class-D power amplifier modules" clipped from review.

[GUTB]

12 hours ago, barrows said:

To add to my above comment:  The VTV standard Purifi amplifier build uses the Hypex demo input board.  This input stage is flawed in at least two ways:

 

1.  It has no input filtering for RFI.  All amplifiers should have RFI filtering on their inputs, and this is especially important for class D amplifiers, where RF getting into the inputs can cause serious, audible, consequences.

2.  It uses ancient, 78xx and 79xx voltage regulators with very poor noise performance and high frequency noise rejection ratios.  The opamp used in the input stage is a high speed precision audio opamp, which requires a very good low noise power supply to perform its best.

 

In comparison, the Purifi Eval 1 and 2 input boards have the appropriate RFI filter circuits at their inputs, and they have onboard very sophisticated discrete voltage regulators designed specifically to provide ultra clean low noise power to the input stage opamps.  These discrete regulators also feature very high power supply rejection at high frequencies, which is critical for a class D amplifier running on SMPS to keep high frequency noise out of the opamps.

 

It is an entirely unfair to evaluate the performance of the Purifi modules based on using them with the Hypex demo input board, and this is why VTV, and other amp builders, offer more sophisticated input board options, with proper input filtering and discrete voltage regulation.

Wait, why would Purifi release a compromised product to the public to represent their brand? Are they deaf? No one can listen to this thing and think it's fine, unless you've never listened to a high end amp before.

[barrows]

3 minutes ago, GUTB said:

Wait, why would Purifi release a compromised product to the public to represent their brand? Are they deaf? No one can listen to this thing and think it's fine, unless you've never listened to a high end amp before.

Purifi has not released any compromised product, please read closely!  The input buffer board used in the basic model of the VTV amplifier you have is made by Hypex, not Purifi.  Additionally, that board was never meant to be used in finished products sold to the public, VTV only does so in order to produce a very affordable amplifier model.

There is a reason VTV offers other input buffers for their amplifiers, it is because those other buffers offer better sound quality.

The standard input buffer boards offered by Purifi: the Eval 1, and the Eval 2 are both excellent, but your amplifier is not equipped with those.

[GUTB]

BTW I went ahead and ordered a set of input boards with Sparkos opamps. I don't want to drill the case, I'll have to figure out an adhesive solution for the standoffs...

[barrows]

38 minutes ago, GUTB said:

BTW I went ahead and ordered a set of input boards with Sparkos opamps. I don't want to drill the case, I'll have to figure out an adhesive solution for the standoffs...

Good move, give at least 100 hours playing time before auditioning, and then give it a listen.  BTW is your source component balanced output?

[GUTB]

16 minutes ago, barrows said:

Good move, give at least 100 hours playing time before auditioning, and then give it a listen.  BTW is your source component balanced output?

Currently a tube pre single-ended only. I do have an active SE-balanced transformer unit which is currently in use with the DAC (Yggdrasil). I also have a Freya which is fully balanced but not in system. Does the Purifi really like to have balanced in?

[barrows]

16 minutes ago, GUTB said:

Currently a tube pre single-ended only. I do have an active SE-balanced transformer unit which is currently in use with the DAC (Yggdrasil). I also have a Freya which is fully balanced but not in system. Does the Purifi really like to have balanced in?

It will perform a bit better with a balanced input if you can provide one.  In the DIY world, there is the option to use the input buffers made by Neurochrome, which are sophisticated enough to convert single ended inputs to balanced before they go to the Purifi module itself, but the buffers provided by VTV, etc, do not do single ended to balanced conversion. How have you connected the single ended source to the balanced input?  Best option is to use a single ended to balanced cable (no adapter) with proper differential wiring: The cable should be a balanced type cable, with a twisted pair inside a shield.  On the RCA end, the center pin should be connected to the hot wire of the pair, the shield should be connected to the shell of the RCA, and the cold wire should be connected also to the shell of the RCA.  On the XLR end, the hot wire should connect to pin 2, the cold wire should connect to pin 3, and the shield should connect to pin 1. By proper wiring like this, the amp will perform pretty well, but will be even better with a balanced source.

[GUTB]

The upgrade input boards and Sparkos opamps came in today. I installed them and the amp is now burning them in. I’ll refrain from posting early observations because those are always defunct within the first day of burning in so I’ll hold off this time. I’ll check in on it regularly to see where it’s at but I plan on giving it at least 100 hours.

[RickyV]

3 hours ago, GUTB said:

The upgrade input boards and Sparkos opamps came in today. I installed them and the amp is now burning them in. I’ll refrain from posting early observations because those are always defunct within the first day of burning in so I’ll hold off this time. I’ll check in on it regularly to see where it’s at but I plan on giving it at least 100 hours.

Curious to know what you think about the opamps. What kind of regulator are feeding them?

[mfsoa]

On 12/26/2020 at 1:20 PM, 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?

 

Check out the Digital Amplifier Company for massive linear Class D. Proprietary modules (not off the shelf consumer stuff). If you want Class D monoblocks each with an 1800 watt linear transformer here you go. Sound quality is superb.

[GUTB]

So, the Purifi is going back.

 

After giving the new input boards and Sparkos opamps several days of burn-in after which it doesn't appear to improve any further I gave it a listen. I tried it with both the Yaqin B-2T all-tube SE preamp and my Freya using all-balanced connections. Digital is from my reference digital source (custom audio PC) to a Yggdrasil Analog 2. Also tried by vinyl system with it.

• Ugly midrange problem: appears to have been solved by the new input boards and opamps. Midrange quality significantly improved and is now almost as good as the reference (Odyssey Kismet / Stratos). Still a little less resolving / muddled compared to the reference.
• Dynamics seems to have improved, but not by a huge amount. It might also be in my head but my perception is that dynamics have improved somewhat.
• No other changes particular stood out to me.

The VTV Purifi with the upgrades appears to be just one step below my Odessey Kismet and Stratos ($1500 used, later $800 used). With upgrades the Purifi is $1400. Essentially this is a budget-performance amp at a budget price. Mind you the Odysseys which are not high-end are still a great value in American hi-fi and if you get them used you can get a decent amp at a budget price. I would say the VTV is reasonably priced for the amount of performance it provides which amounts to "okay". This technical performance. There is one other issue that is absolutely killer:

 

The total lack of engagement. I tried listening to it, but from start to end, I felt like I was forcing myself. I was never involved or engaged in the music. At first I was willing to consider that it was the ugly midrange problem which was doing it. But after that was solved there appeared to be no other excuse. Dynamics, microdetails, etc, is just one step down from the reference. They're fairly close. I fixed the cables and tested various configurations, nothing helped. I just didn't enjoy the sound, and that reason had no particular reason related to sound technicalities. In the end -- it's the usual, traditional death blow to class D, fatigue. There's something it does which is murder on the ear-brain system. I used to associate that with the lack of bandwidth and destructive output filter. I was told that self-oscillating amps don't have this issue by doing the filtering by using feedback; I have no idea how that works but if it's true then there's something else doing it. But it's still there. Basically it's still unlistenable.

 

Those of you who think you like your class D, I recommend being honest with yourself. Do you REALLY enjoy listening to you music? When was the last time you turned on your class D and got sucked in? Has it ever happened? Is your system spending more and more time left alone and you tell yourself it needs this or that upgrade? Once again I'm forced to accept that class D has serious killer problems and I doubt it's a phenomena I'm alone in experiencing. I don't think it's matter of discernment or having experience with high-end audio.

[barrows]

1 hour ago, GUTB said:

So, the Purifi is going back.

 

After giving the new input boards and Sparkos opamps several days of burn-in after which it doesn't appear to improve any further I gave it a listen. I tried it with both the Yaqin B-2T all-tube SE preamp and my Freya using all-balanced connections. Digital is from my reference digital source (custom audio PC) to a Yggdrasil Analog 2. Also tried by vinyl system with it.

• Ugly midrange problem: appears to have been solved by the new input boards and opamps. Midrange quality significantly improved and is now almost as good as the reference (Odyssey Kismet / Stratos). Still a little less resolving / muddled compared to the reference.
• Dynamics seems to have improved, but not by a huge amount. It might also be in my head but my perception is that dynamics have improved somewhat.
• No other changes particular stood out to me.

The VTV Purifi with the upgrades appears to be just one step below my Odessey Kismet and Stratos ($1500 used, later $800 used). With upgrades the Purifi is $1400. Essentially this is a budget-performance amp at a budget price. Mind you the Odysseys which are not high-end are still a great value in American hi-fi and if you get them used you can get a decent amp at a budget price. I would say the VTV is reasonably priced for the amount of performance it provides which amounts to "okay". This technical performance. There is one other issue that is absolutely killer:

 

The total lack of engagement. I tried listening to it, but from start to end, I felt like I was forcing myself. I was never involved or engaged in the music. At first I was willing to consider that it was the ugly midrange problem which was doing it. But after that was solved there appeared to be no other excuse. Dynamics, microdetails, etc, is just one step down from the reference. They're fairly close. I fixed the cables and tested various configurations, nothing helped. I just didn't enjoy the sound, and that reason had no particular reason related to sound technicalities. In the end -- it's the usual, traditional death blow to class D, fatigue. There's something it does which is murder on the ear-brain system. I used to associate that with the lack of bandwidth and destructive output filter. I was told that self-oscillating amps don't have this issue by doing the filtering by using feedback; I have no idea how that works but if it's true then there's something else doing it. But it's still there. Basically it's still unlistenable.

 

Those of you who think you like your class D, I recommend being honest with yourself. Do you REALLY enjoy listening to you music? When was the last time you turned on your class D and got sucked in? Has it ever happened? Is your system spending more and more time left alone and you tell yourself it needs this or that upgrade? Once again I'm forced to accept that class D has serious killer problems and I doubt it's a phenomena I'm alone in experiencing. I don't think it's matter of discernment or having experience with high-end audio.

Sounds like you prefer highly distorted and colored sound, there is nothing wrong with that, as long as you are willing to admit it.

[R1200CL]

1 hour ago, GUTB said:

Those of you who think you like your class D, I recommend being honest with yourself. Do you REALLY enjoy listening to you music? When was the last time you turned on your class D and got sucked in? Has it ever happened? Is your system spending more and more time left alone and you tell yourself it needs this or that upgrade? Once again I'm forced to accept that class D has serious killer problems and I doubt it's a phenomena I'm alone in experiencing. I don't think it's matter of discernment or having experience with high-end audio.

You should try my Theta Prometheus mono blocks 🤪

[fas42]

1 hour ago, GUTB said:

Those of you who think you like your class D, I recommend being honest with yourself. Do you REALLY enjoy listening to you music? When was the last time you turned on your class D and got sucked in? Has it ever happened? Is your system spending more and more time left alone and you tell yourself it needs this or that upgrade? Once again I'm forced to accept that class D has serious killer problems and I doubt it's a phenomena I'm alone in experiencing. I don't think it's matter of discernment or having experience with high-end audio.

 

Class D can deliver satisfying sound ... my current, very cheap Edifier active digital speakers, using very ordinary class D chip amps of some variety, are doing quite nicely - they largely get out of the way of the sound of the recording; I'm close to hearing only the signatures of the recordings spaces and environments. BUT, like all setups, they need some level of tweaking - if this is not done, then only luck, or extreme care in selecting good combinations of components will likely lead to a thumbs up.

 

My experiences to date tell me that anything that relies on high frequencies in its operation, which means DACs and class D amplifiers, are very sensitive to noise on the mains, and other cables - pristine waveforms are essential; anything less is highly likely to be the kiss of death - and lead to the "lack of engagement" issue.

 

The "killer problem" is the poor understanding by most with technical knowledge of how important it is to get these things right - you can't get away with the shortcuts and lack of attention to detail that circuits operating essentially always at audio frequencies will allow - vinyl and class A, no global FB amps may have easily measurable distortions; but the ear/brain can easily account for, and discard these.

[GUTB]

46 minutes ago, barrows said:

Sounds like you prefer highly distorted and colored sound, there is nothing wrong with that, as long as you are willing to admit it.

In reality, the sound from the Purifi is less resolving and more muddled than from the Odysseys, with or without tubed preamps and with digital or vinyl. It's not awful (after upgrading the input boards) but if you think this is high-end sound you honestly don't know what high-end sound is. Odyssey amps are good, but I've heard better. I also wouldn't describe the sound of the Purifi as being dry, cold or lifeless unlike most other class Ds have struck me as. I believe Purifi had solved that particular problem. But the death-blow to class D remains, the utter boredom and lack of engagement. I can't narrow it down to a particular technical aspect as technically speaking it's okay across the board. The only thing I can come up with is that something about class D is ugly to the ear-brain system which causes listener fatigue.

 

I gave this more than a fair shake. It was found wanting in the end. From a technical perspective the sound was what most would consider "good". It's true that I have higher expectations than many on the forum, but even I can't point to any technical aspect of the sound and call it "bad". Dynamics, microdetail / resolution was a step down from my reference, but just a step. The horrible midrange was solved by the input board and opamps. I guess it images unusually high, but I don't think that's a deal-breaker and besides that it imaged just as well as my reference. Perhaps even the dynamics could be helped by an upgraded power supply. Maybe higher-end opamps could even bring the resolution up to reference. But the killer fatigue IS a deal-breaker, and opamps won't fix that. Tubes didn't fix it as my all-tube preamp using all NOS tubes didn't change that. You can blame it on my personal preference but I think perhaps you should open your mind the possibility that class D still garbage due to intrinsic flaws in the technology which haven't been solved yet. I may still try the the other GaNFETs, those might legitimately be game changers. The Cherry amps might be the lone exception as well as they use some kind of parallel switching tech that allows them to get much higher bandwidth than traditional possible. I have a little Cherry stereo amp but it's too weak for my speakers so I can't really use that as a reference to make a judgment call on it, but I will say that it also has a full tonal quality similar to the Purifi and unlike other class Ds.

[GUTB]

30 minutes ago, fas42 said:

 

Class D can deliver satisfying sound ... my current, very cheap Edifier active digital speakers, using very ordinary class D chip amps of some variety, are doing quite nicely - they largely get out of the way of the sound of the recording; I'm close to hearing only the signatures of the recordings spaces and environments. BUT, like all setups, they need some level of tweaking - if this is not done, then only luck, or extreme care in selecting good combinations of components will likely lead to a thumbs up.

 

My experiences to date tell me that anything that relies on high frequencies in its operation, which means DACs and class D amplifiers, are very sensitive to noise on the mains, and other cables - pristine waveforms are essential; anything less is highly likely to be the kiss of death - and lead to the "lack of engagement" issue.

 

The "killer problem" is the poor understanding by most with technical knowledge of how important it is to get these things right - you can't get away with the shortcuts and lack of attention to detail that circuits operating essentially always at audio frequencies will allow - vinyl and class A, no global FB amps may have easily measurable distortions; but the ear/brain can easily account for, and discard these.

 

I was using my reference mains which is a Lessloss level 1 filtering cable + Lessloss Firewall 64X plugged into a Furutech outlet. My listening room has only audio gear plugged in and no lights / fans turns on. I suppose I COULD try it through my 500VA balanced isolation transformer before I pack it up...but I had tested it against a stock black cable plugged into another common outlet in the room and I don't think there was any difference. On my reference there were large upgrades to sound with this setup.