Purifi Class D: Junk?
My preamp has an output impedance of 230 Ohms. A preamp with 230ohm output impedance will drive anything, even a low gain one, if you get high enough volume. And even drive a buffer with 2.2kohm input impedance "if correct", I can’t believe it is though. 47kohms has been the industry standard since time began, and tube amps were 100kohm Cheers George |
Well if that’s the spec that would certainly help explain the result. Does not mean it’s junk just that there is a system mismatch. Inexpensive Class D amps usually just provide a stock circuit in a box I have an $80 Fosi Class D integrated amp (with Bluetooth) in a small setup driving a pair of refurbed Boston A40s. It uses a stock TI Class D chip. The sound is very good there in a suitable application. |
The 2.2kohm is single ended input to ground, what the amp sees. That’s simply the amp module without an input board connected. The evaluation board that manufacturers use on the amps has a 10.2kohm differential input impedance. In other words you need to know what board VTV used to know what impedance the preamp sees. |
Does not mean it’s junk just that there is a system mismatch.230ohm into 2.2kohm is fine, 1:10 ratio, and if he has enough gain there is no problem. "unless" there is a coupling capacitor on the preamp's output that's too small, and rolling off the bass, because the output impedance goes even higher than 2.3kohm at low frequency. This will cause the thin sound. Cheers George |
I bought it without the custom input board. It uses the standard Purifi board's input and buffer, which apparently isn't bad. I didn't bother spending a bunch on custom input boards and buffers because I figured this will at least give me a fundamental grasp of the sound. Custom buffers shouldn't make or break the sound, should they? |
My Audio Research sp-16 has 240 ohm output impedance into Bel Canto ref1000m amps. These have 100kohm input impedance with the BC input stage versus 10k ohm for the stock Icepower module used solo on the ref1000 model. That is to provide good performance with most any preamp including higher output impedance tube preamps. So yes special input stages are done for a reason and do provide significant better performance in many cases. |
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. |
This thread reads so much like Ghost Hunters it’s making me nostalgic. https://www.imdb.com/title/tt0426697/ |
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. This is sounding like snake oil to me. |
No doubt, to those that do not listen. Those that listen with an open mind....they actually experience something......so they really KNOW. Most high end audio is the blind (or deaf....he he) leading the blind. What I mean by this is practically no one actually does listening tests at the micro level. Most just A/B components and make generalizations and guesses. In drag racing there is only 5 things that matter.....horsepower, weight, drag, traction and gearing. And these things can be all measured. In high end audio there are an infinite number of things that change the sound that cannot be measured. Unless you actually A/B wire.......you cannot know about wire.....unless you actually A/B removing a non needed AC filter and replacing it with a great sounding AC inlet then you do not know what it does......on and on....into infinity. The switching power supply that in the VTV and a lot of other Ncore and Purifi based amp has two poles of AC filtering built in......why would you want to add smaller inductors before this and encase them in a STEEL case? You already have some good filtering. More is not better unless it is done at a super level. Have you ever removed a power switch from a power amp and listened? In the VTV the switch is a two pole.....so there is a switch on the hot and neutral......Have you ever tried a super fuse? If you have not you know nothing about the sound of fuses.....on and on. This game is not simple. Every single thing you do makes a sonic difference. I have been tweaking since 1976......I first removed fuses from the original Theta DAC back in the late 80s and heard how bad the fuses were. This is not new information. Most reading this have no idea what I am talking about because they have never done these kinds of tests. Only about 5% of audiophiles are DIY people and out of those maybe 5% of those really do serious listening tests.....So, we are talking about a very, very small percentage of people that do serious micro stuff listening tests. Back in the 50s and 60s the audio game was way more DIY oriented. You could go into any "hifi shop" and buy individual speaker drivers, xover parts, tuner parts, kits of preamps and amps from various manufacturers, etc. Today......very few have any idea how anything works.....just plug and play. This is why the game is so complicated because there are no rules.....it is just every man for himself and there is no consensus on practically anything. If you look at dragsters....they all look like the same person made them all.....because the dragster people all KNOW what works....and they mostly agree. High end audio is just the opposite. However, if you are smart and read a lot you can find gear for very little that will blow your mind and make you cry and feel the love and joy of life tingling in every cell of your body. |
Yes, I believe in fuses........as in BE and LIVE together. A belief without an experience is like reading a novel and thinking you know about love. Words are not an experience. To KNOW anything in audio.....you have to listen....and with an open mind.... When I post about something it is because I have experienced it. If you post about something you have not tested....then you are just guessing or wanting to be right or heard......belief systems are bogus.....we need to BE LIVE our truth. |
Seems these guys are “fusers”. Some of the rationale makes sense IMO. https://www.stereophile.com/content/hifi-tuning-fuses |
Once again on fuses for the gullible here that are thinking of throwing their money away paying $150+ for a 50cent fuse that’s just been dressed up to look glitzier. You’ll never see the manufacturers of these (snake oil) fuses defending themselves or their products with the claims made on forums like these. Just change the fuse if old fuse for a quality brand EE industry standard 50c fuse, as all fuses (even the snake oil ones) do age and still work but develop corrosion, sag and distort etc after too many turn on cycle surges. Cheers George |
You are making people wrong by telling the world that they are gullible. Why would you put someone down for their EXPERIENCE? I may not agree with what everyone says but I practically never doubt what they say about what they hear. They could of had expectation bias or maybe had a cold that day but 95% of the time they actually heard what they say. I have done tons of A/Bs with multiple people in the room and NEVER did anyone hear something different. Back in the late 70s three humans, including me, A/Bed 10 brand new Supex cartridges......We all heard the differences and one of them was the best......The frequency response graphs that came with each cartridge showed no correlation to the sonics. I trust what George (and everyone) says about what he/they actually hears.....I do not trust what he/they says about things that he/they has not heard......why would anyone? Trust your experience.....trust others experience...do not trust opinions based on non experience. Please, love yourself and everyone. Allow everyone to have their own experience without putting them down. |
It is a fact that the middle of the herd is not the top of the mountain or the peak of endeavor. No matter how much the middle of the herd may look around and try to convince itself of that by looking at those (others) which may be similar and comfortable. Hearing is one of those things that is not perfected in measurement or meaning, not by a long shot. Therefore we have no perfect correlation in measurement that can fit what we hear. Hearing is a thign that is a massive variable in quality and capacity tied to the brain, in discernment, a variance a great as the variances in human intelligence. And human intelligence can span a difference as large as a million to one, in cognitive speed differences. Seriously. that huge a range. (add 5 IQ points, halve the cognition rate or speed). Hearing is tied to this, and is similar. not the same, bit similar. connected to it. Thus hearing has a IQ connection or quotient of a sort. Not all ear/brains are the same. There is a range, of capacity, for discernment. differences between individuals. To add, part of our hearing is self trained, self created. So.....the map is not the territory. This point is ultra critical to understand. But we can still have peaks and we can still have average. And it is noted that the average of what Class D is, has not yet taken over the peak of quality in the world of high performance audio. Specifically, it is not at the peak..for the ears that want that mountain peak of quality. It may do so in the future and it may not. Who knows. The peak may move further away from where class D is headed. It’s a moving, living, breathing, growing, changing target. I’ve torn down Class D amps and spent about 2 years of my life, off and on, trying to make it sound better. Via analyzing the electronic parts, their function and what they are doing wrong, and what changes are needed and then doing what I can. To improve the correlation between what they do and the psycho-acoustic model of the ear, what that ear requires. And I made some great Class D amplifiers. So good that many folks thought the modded out versions that made it to an audio show, were among the best they’d ever heard. If not the best. But they still did not compete with the best of the standard model of audio amplification, be it class A or class a/b, or tube based versions. They just don’t have it. I could get into the psycho-acoustic modelling and how that compares to what Class D is doing wrong, and how to deal with it re changes to the design of class D, and that would help people a lot. It would help designers and end users. But that information is valuable, hard fought for... and it is my life blood in the world of putting food on my table ----and this is business. Some day, Class-D, some day. Never Know. But.. not yet..not yet. |
That is your opinion based on your experience......this is great.....I respect that. However, read the reviews of the Technics, AGD, Merrill and LKV class D amps.....those reviewers are NOT saying what you are. They think these very latest (and expensive.....starting at $7500) do compete directly or are even better than their money equivalent class A, class A/B or tube amps. Please read the reviews. The goal now, is to make a lower priced amp that is as good. I hope mine is. We will find out soon. I am not saying the best of the latest Class D is as good as the very latest most expensive class A or A/B amps. The most expensive cllasss D I mentioned are the Merrill 118s at $36K. There are lots of exotic amps above that price point....like the big Dagostino, Constellation, Gryphon, Audionet, Boulder, Dartzeel, VAC, etc. etc. Yes, some of these exotica are no doubt better in some ways than the above mentioned Class D amps. However, most reading this will never buy......nor can afford any of these amps. But if there can be a class D amp under $3K that competes with $20K amps....then a lot of people will get really good sound (and less heat) for something most of us reading this can afford. |
So, the question is, does this VTV really represent a baseline of what the latest class D can do? The LKV seems interesting but for that money you could get a used Mark Levinson 585, will this really compete? Also in that price range is the big Cherry amp with a beefy linear power supply. Frankly this price point seems way too high. If they can compete with good A or A/B designs at the same price point that would be one thing. But the Stratos is by no means a pinnacle amp, not even close. If the VTV can at least compete with the Stratos which I bought used for $800 shipped than I may switch over to VTV or something similar, perhaps get @ricevs to mod it, and then see where the upgrade road takes me from there. The other factor is there can't be listening fatigue. That's something I can only judge with long-term listening. I don't care how impressive the sound is technically, if its fatiguing than it's TRASH even if it costs $1.50. |
I trust what George (and everyone) says about what he/they actually hears.....I do not trust what he/they says about things that he/they has not heardOne needs both listening/measuring, you need to back up what your hearing with measurement’s otherwise your just saying "trust me" I heard it which is subjective only. To all buying/modding anything, there’s not one piece of half decent audio equipment that’s any good, that has not been designed using all the EE laws and test/measurement procedures, if it hasn’t I would give them a wide berth. Especially modders that don’t give any EE measurement/bench test proof on what they’ve done to back up their subjective mods, these guys are just "snake oilers" and usually fusers saying trust me. Cheers George |
To all buying/modding anything, there’s not one piece of half decent audio equipment that’s any good, that has not been designed using all the EE laws and test/measurement proceduresReally? Not one? Huh. Guess they all must be perfectly designed then — and certainly no room for further improvement. There are these pesky things called cost constraints though. these guys are just "snake oilers" and usually fusers saying trust me.Well that’s just an over-generalized and ignorant statement. Not everything that provides an improvement is necessarily measurable. You don’t like guys who mod equipment. Fine. That doesn’t mean all or most of them are bad. If they’re not good they fail, and if they’re good they do well like any other business. The market is the final arbiter of whether a mod is “snake oil” or not. Not you. |
Really? Not one?So you would purchase an audio product that was not designed using the Electronic Engineering laws and bench testing?? Good luck with that sunshine. Or maybe you need to comprehend a little bit better there’s not one piece of half decent audio equipment that’s any good, that has not been designed using all the EE laws and test/measurement procedures. |
So you would purchase an audio product that was not designed using the Electronic Engineering laws and bench testing?? Good luck with that sunshine.Maybe you need to comprehend better, sunshine. Just because something was designed using the laws of whatever doesn’t mean it was designed optimally or with the best parts. Hence, they can still be improved upon through modding, which was the whole point. It’s not all “snake oilers” as you assert. |
Alright, it is "sunshine from down under" on yet another Class D thread.Problem with george is, he feels we should trust his hearing and not our own. Ask him for concrete evidence on Class D stuff, and he will cry uncle and start posting Nelson Pass's quotes. He does not have the full knowledge of class D. If you don't believe me, just wait for this thread to move on a bit OR go to other class D threads. And on top of that he calls on others as "policing" when he does the most himself. Looking at his past posts, I think he has some issues. Like digging up 13 year old posts and start calling out names. I suggest, ignore his posts and move on. |
Ask him for concrete evidence on Class D stuff, and he will cry uncle and start posting Nelson Pass’s quotes.Shows what you know, think before you show your lack of................ That’s for an entirely different audio product not class-D. Stuff I post on Class-D’s Achilles-heel has to do with switching frequency and it’s filter and noise But seeing you bought up Nelson Pass’s quotes, here are his on Class-D, that I’ve never put up. Nelson Pass (Threshold, Passlabs)And just for good measure Conrad Johnson Lew Johnson (Conrad Johnson) Cyrill Hammer (Soulution) "if you want to have your product performing at the cutting edge it is not possible with today’s known switching technologies. In order to come close to the performance of the best linear design we would need high-current semiconductors that provide switching frequencies of several MHz or even GHz." And there are quite a few more, if you want me to keep going? Cheers George |
because of the false initial proposition on which it was based.Sez you, he has a valid but crude way of putting it. Technics so far with the SE-R1, are the only ones that have addressed the Achilles-Heel of Class-D. Output Filter, Noise, Phase Shift. All related to the Switching Frequency. By utilizing GaN Technology to it’s fullest, and having (3x higher) Switching Frequency, and eliminating the 3 Achilles Heels above from effecting/influencing down into the audio band frequencies. Cyril Hamer of Soulution- Audio at the bottom of my last post says it also. Cheers George |
So, burn-in continues. There's a troublesome mid-range artifact, a harshness / blurriness that shows up in voices with "hot" recordings. Also the image seems to project especially high, but I'm not sure if that's the amp or something with the speakers because I did move them yesterday. If this midrange issue doesn't fix itself with continued burn-in then it'll have to go back as I know this will kill it for me, it's very uneuphonic. Maybe a custom input buffer option fixes it if this continues to be a problem, we'll see. |
He’s tried a few, and been on a disillusionment path with them, it’s expected to not feel confident with this one. I’m surprised he’s given them as much chance as this. I know what Class-D would probably make you happy madavid0 OP, and that’s the Technics SE-R1 if you want to give that a go, hard to get one but possible. Cheers George |
There’s also a new approx $10K integrated Class-D from Technics called the SU-R1000 Integrated Amplifier around 22 kg . Said to have many of the GaN Class-D features of the far bigger SE-R1, but nowhere yet can find if it uses the 1.5mhZ switching frequency that "makes" the SE-R1. Also it uses smp power supplies, even though it’s 22kg, Unlike the SE-R1 at some 60Kg because of it linear supplies. No reviews or measurement tests as yet for this one from Technics Cheers George |
I'll look around the local dealers to see if they have a SE-R1 for audition. I really am giving class D a lot of chances. Maybe I really want to believe in the promise of high-quality audio in a small and cheap package. But I didn't go into this with my mind made up, I was successfully talked into trying it by you guys (and others). I really have to question though what are some of you guys' standards in audio. It's still burning in so we'll see. I hope this mid range mess sorts itself out. |
You buy the bottom of the line VTV amp and you think you will know anything about class D or Purifi? This amp is $979 delivered including shipping. It uses a one dollar op amp for the input buffer (LM4562) and two one dollar 3 pin regulators.....here is the part listed on Hypex site: https://www.hypex.nl/product/nc500-evaluation-board/51 This is NOT going to give very good sound. The input board from Purifi is better....at least it uses 1612 op amps and a discrete regulator. However, the input board that VTV makes that uses discrete op amps and discrete regulators is much better sounding than the Purifi board. In fact, I will not mod any VTV amp that uses the stock Hypex input board. This is not serious....this is for people who want to spend as little as possible. The discrete input board will take the amp up another level....but my mods take the amp to many more levels up. You are just playing around with that VTV. I will have an eval amp out for tour....so you guys can really hear what class D and Purifi can do. A fully modded stereo VTV Purifi amp using modded Sparko labs op amps is around $2600.........not cheap....but a lot less than a $10K LKV. |
Maybe send it to @ricevs to do some magic mods to itDon’t know about mods without any tests/measurements/to back up any subjective listening claims. But "voodoo" and "snake oil" maybe. As for the LM4562 it one of the better opamps around, it’s even used in some discrete MSB dacs and many others. And as for your OPA1612 is no better and cost around the same. Just more "snake oil" talk from Tweakaudio, EVS or whatever you call your self these days |
It is best just to ignore George. He goes on and on saying the same nonsense about stuff he has never listened to. Let him have the last word or it will go on forever......go on George, you know you have to. Maybe we should use a new word for people like this. How about Anti Snake Oiler or ASO. Much better than "fuser" (word made up by George to vilify fuse lovers). If you look closely you will see the humor.....he he. I love you George. You are so entertaining. |
More like calling you out, on your snake oil mods, that you don’t backup with any measurements, just a fusers "trust me it works"So if there aren’t measurements it can’t work, eh? Guess you can’t just trust your own ears without some kinda measurement for justification — is that it Georgie? Are you really that insecure about your own hearing and/or listening ability? I bought Ric’s original Millennium DAC decades ago and it still works and sounds great, even without measurements. Hundreds of audiophiles have bought his products and his mods, and he’s earned lots of praise and a solid reputation doing it. Measure that Georgie. And by the way, what the hell have you ever produced other than half-assed, armchair quarterback criticism of other people’s work? Keep on measuring Georgie while the rest of us enjoy listening. |
So if there aren’t measurements it can’t work, eh?No, it means they don’t know what their doing if non are done and presented, so give this kind of modder a very wide berth, "could" even be dangerous to the owner let alone the equipment. Measure that Georgie.Measurements/testing is half the story, listening to what was done is the other, and if you don’t like it, mod again using measurements and test once again, till your happy with both. That’s how any decent piece of equipment is developed. not with snake oil and voodoo and "trust me’s" Keep on measuring Georgie while the rest of us enjoy listening.Keep on doing both listening/bench testing and measuring as they very much do! back each other up. |
