Purifi Class D

4 hours ago, GUTB said:

 

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.

What I do if I want good understanding of how much mains or other interference may be a factor is to completely shut down the house electrically - also, no smartphones or other wireless devices operating. A further step is to pull the fuses, or circuit breakers in the switchboard, meaning only the circuit feeding the audio is functional - and every device and cord is pulled out of that circuit, apart from the audio components. The point is to completely silence the house electrically, and minimise any cable acting as an antenna. ... Does this make a significant difference? If the SQ does improve, then restore the electricals a step at a time - to get understanding of where the interference degrading the sound is coming from.

5 hours ago, barrows said:

Well, we are of a different opinion here.  As one who has actually worked in the industry for over 20 years now, visited countless dealers all over the country, listened to their showroom systems, listened to the in house demo systems of manufacturers such as Ayre Acoustics, PS audio, and Avalon Acoustics, as well as attended many CES shows, and RMAF shows, I am pretty sure I have a very good idea of "High End Sound", of many different stripes even.

I am OK with you suggesting that you do not like the sound of this specific amplifier, you are entitled to your opinion.  But when you suggest that my experience is lacking, you are just plain wrong.

 

In my system, the first class D amplifier I heard which could play on a  level playing field with very good class A and A/B amplifiers was the Ncore, in fact, after comparing Ncore with my Pass Labs X.5 series amplifier the Ncore amp had the better sound overall, the Ncore amp also bested the highly regarded PS Audio BHK here.

More recently, even better class D became available from Purifi.  My Purifi amplifier beat out my Ncore amplifier quite easily, as it features slightly more refined high frequency reproduction, while retaining all the other qualities I liked so much with Ncore.  The only class A/B amplifier I have heard here which I consider a tiny bit better than the Purifi is the Bricasti M25, which retails for $18,000.  If I had the opportunity to own the M25 I would accept it. 

Everyone is entitled to their opinion but the question is if it’s a fair comparison vtv gain stage vs eval1 gain stage ( also modified).

The reason I am interested in these Purifi amps is I am looking for a power amp to drive my Raal headphones. For financial reasons I can not just buy  some high end integrated tube amp so have to do things in stages. I have two possibilities one is that my pre-amp has two pairs of rca outputs. One for the speaker amp and one for the Raal amp (stage 1). Stage two could be buy a second xlr  (tube) pre-amp. XLR so I can connect it to the xlr output of my DAC. 
The second thing I am thinking about is if I am going to build a Purifi amp to build it with a transformer power supply instead of the smps. Could that be beneficial? I like the idea.

Any ideas on this?

51 minutes ago, RickyV said:

The second thing I am thinking about is if I am going to build a Purifi amp to build it with a transformer power supply instead of the smps. Could that be beneficial? I like the idea.

Any ideas on this?

There is no reason that a linear power supply would perform better powering the Purifi amp modules.  So far, the class D amps which have used linear power supplies for the output stages have proven to offer no better performance because of such, and in fact, the measured performance, especially noise, usually suffers due to magnetic coupling of the large power transformer required with the amplifiers output (see Stereophile measurements of the LKV Veros).  Note that Chord makes their top level class A/B amplifiers using SMPS for just this reason, they actually produce a lower noise floor because they eliminate this problem.  Good, well designed SMPS (not cheapo Chinese wall warts) are not nearly as "evil" as most audiophile mythology makes them out to be.  It makes me wonder if the audiophile desire for extremely large, heavy, wasteful, and antiquated designs is actually some sort of personal compensation for inadequacies in other areas.

I do run a custom linear power supply to power the input stage of my Purifi build though.  I did this because it was relatively easy to do (I design high performance low level linear supplies in my work), and there was no disadvantage in doing so, as the small transformer and currents required would not create a noise problem like powering the output stage does, and because a totally separate power supply for the input stage might make an audible improvement vs. using the aux supplies of the main SMPS for this.  My custom supply is a fully linear, +/- 18 VDC supply using ultra low noise discrete regulators.  But I have not made any comparisons, the amp sounds fantastic though, using the Purifi Eval module for the input.

17 hours ago, fas42 said:

 

What I do if I want good understanding of how much mains or other interference may be a factor is to completely shut down the house electrically - also, no smartphones or other wireless devices operating. A further step is to pull the fuses, or circuit breakers in the switchboard, meaning only the circuit feeding the audio is functional - and every device and cord is pulled out of that circuit, apart from the audio components. The point is to completely silence the house electrically, and minimise any cable acting as an antenna. ... Does this make a significant difference? If the SQ does improve, then restore the electricals a step at a time - to get understanding of where the interference degrading the sound is coming from.

Okay so I plugged my reference mains into the input of the 500VA balanced isolation transformer and the VTV into one of the outlets using an Audio Envy power cable.  This is the transformer I have: https://aliexpi.com/ugvH

Also, by happenstance, I got in a new preamp, a Mbl 6010 clone: https://aliexpi.com/pxKz

The new preamp has balanced input and output and low noise / distortion specs. I thought I'd throw this into the chain as well. The Freya is high-bandwidth and has a JFET buffer stage option, but I never trusted I was getting good results from this unit. It's been burning in for a day now.

So, there MAY be something to this power quality argument. I listened to some tracks, some Bluegrass that makes me especially happy to see if engagement has improved. And....I think there may be an improvement. I felt I was able to get into it at least somewhat, something that the amp has failed to do up until now. Maybe the preamp has something to do with it. So I'll hold off on returning it just yet. Dynamics are even worse but that has to be the preamp burning in (I hope and I don't need a larger transformer and those get pricey to ship from China).

On 1/13/2021 at 4:13 PM, GUTB said:

So, there MAY be something to this power quality argument. I listened to some tracks, some Bluegrass that makes me especially happy to see if engagement has improved. And....I think there may be an improvement. I felt I was able to get into it at least somewhat, something that the amp has failed to do up until now. Maybe the preamp has something to do with it. So I'll hold off on returning it just yet. Dynamics are even worse but that has to be the preamp burning in (I hope and I don't need a larger transformer and those get pricey to ship from China).

 

Sounds promising ... one always has to be very careful with changing more than one thing at a time, of course - the reasons why the SQ has changed may not be properly understood; so, undo, or redo only a single change of part of the chain at any one time, to try and confirm what the pattern is.

On 1/12/2021 at 11:42 PM, barrows said:

My custom supply is a fully linear, +/- 18 VDC supply using ultra low noise discrete regulators.  But I have not made any comparisons, the amp sounds fantastic though, using the Purifi Eval module for the input.

Hi Barrows, that's interesting. I don't know how to build my own power supply. So I'm using the +/-18V the SMPS1200 provides. 

I do have an unused dual rail LT3042 regulator lying around: https://www.mpaudio.net/product-page/sd-hpuln-ps. 

Your post made me thinking I could put this in between smps and Eval1 input. Only its slightly under spec. Smps Vaux is 2x22V, Eval1 input is +/- 18V where the sd-hpuln-ps does max 20Vdc in and 15Vdc out (at 2x 1,5A). So I'm afraid it was an interesting thought, but not feasible. 

FWIW, I'm using the Eval2 buffers, and at first I was using the unregulated output from the Micro Audio SMPS (their 1k PFC version).  Eval2 contains LT3045/94s.  Their PSU alone was a good improvement over the Hypex equivalents using the 25v unregulated output (regulators didnt even get warm). 

Finally got around to using the regulated 18v outputs on the same PSU, significant step up.  So yes worth feeding that modulator side clean regulated voltages, even if you have good regulators.

2 hours ago, guiltyboxswapper said:

Micro Audio

I have never heard about these smps, what’s the difference with hypex?

 Edit:  Do you by any chance know if Purifi is designing their own smps? I thought I read that somewhere.

6 minutes ago, RickyV said:

I have never heard about these smps, what’s the difference with hypex?

https://micro-audio.com/store/product/smps1k-pfcr2/ 

Firstly you get a couple of capbank PCBs which you can locate right next to the Purifi modules- mine came with Elna audio grade (gold), but in time I'll switch in my Mundorf AGs of the same size.

Physically much bigger too, and as you can see from the pictures uses good quality components across the board.

SQ subjectively its a considerable improvement, especially once you plug in the 18v regulated into the AUX of your buffers.

Some of us are using Micro Audio PSUs on DIYAudio too.

5 minutes ago, guiltyboxswapper said:

especially once you plug in the 18v regulated into the AUX of your buffers.

wouldn’t it be better if the aux was done with HQ linear regulators like @barrowshas done.

14 minutes ago, RickyV said:

wouldn’t it be better if the aux was done with HQ linear regulators like @barrowshas done.

Kind of, but the Eval2 already has LT3045/94 regulators on the card which are local to the amp's modulator (better impedance / response potentially through shorter native PCB path), and even fed 25v they don't get warm at all.  They did appreciate the 18v regulated supply though for sure.

edit: the point about them not getting warm even at 25v means the onboard LT regulators are very much in their sweet spot (well under 100ma load), and highlights how little current is being consumed by the modulator/aux side.

I am just waiting for Bruno to finish his new more powerful Purifi modules.

What about power supply is Purifi designing a smps? Preferably a high frequency switching one.

9 hours ago, Mike48 said:

I've been listening to a pair of Apollon monoblocks made with the 1ET400A modules for a month now. To my ears, they are the most transparent and neutral amps I've heard, with the smoothest and flattest treble. Their output is load invariant, which works exceptionally well driving my electrostatic speakers. Oh, and the bass is remarkably strong and detailed, also.

 

I can see that those who have been listening to something less neutral might miss the colorations. It's the same way that one can get accustomed to the sweetening of MQA, the crosstalk in LPs, or the rising high treble of some MC cartridges. Pleasant distortions are easy to get used to and hard to leave behind.

 

And other amps may have other styles of sound that also are excellent but are different.

 

In my opinion, the PuriFi amp module is a noteworthy achievement and can be used to make an amp with outstanding sound.

What do they sound like with your turntable? 

I'm interested to hear what you think about the Weiss op amps. I recently completed a DIY build of a pair of monoblocks using the Purifi modues with Neurochrome buffers. I decided to go with a large linear power supply because I was disappointed with the performance of my last class D amps (Nord NC500 with Hypex SMPS), and also since I could build it myself. So far, I'm liking the Purifi amps much more than the Nords. Much better dynamics and sound staging, and a smoother, airier midrange and high-end (although my old ears don't hear high frequencies like they used to). The amps currently have a few hundred hours on them, so they may still have a bit more break-in to go.

Each monoblock has a 1500VA custom Toroidy transformer with approximately 200,000uF of filter caps (CRCRC for high voltage rails, CRC followed by low noise regulator for buffer stages). 

The Neurochrome buffers are very neutral sounding with very low noise and distortion, but I'm wondering whether an input buffer that adds a little more character would be preferable (I like to experiment). So I'm considering building (or buying) an input buffer with the Weiss op amps, or maybe VTV's tube buffer. 

43 minutes ago, jaytor said:

I'm interested to hear what you think about the Weiss op amps. I recently completed a DIY build of a pair of monoblocks using the Purifi modues with Neurochrome buffers. I decided to go with a large linear power supply because I was disappointed with the performance of my last class D amps (Nord NC500 with Hypex SMPS), and also since I could build it myself. So far, I'm liking the Purifi amps much more than the Nords. Much better dynamics and sound staging, and a smoother, airier midrange and high-end (although my old ears don't hear high frequencies like they used to). The amps currently have a few hundred hours on them, so they may still have a bit more break-in to go.

 

Each monoblock has a 1500VA custom Toroidy transformer with approximately 200,000uF of filter caps (CRCRC for high voltage rails, CRC followed by low noise regulator for buffer stages). 

 

The Neurochrome buffers are very neutral sounding with very low noise and distortion, but I'm wondering whether an input buffer that adds a little more character would be preferable (I like to experiment). So I'm considering building (or buying) an input buffer with the Weiss op amps, or maybe VTV's tube buffer. 

First welcome to Audiophile Style. Second what a very nice build you made.

Why did you choose a 1500VA transformer wasn’t 600VA enough? I am asking because I may want to build something similar. Have you tried Micro Audio smps, they suppose to be better then hypex? 
what input buffers are you using now?

3 hours ago, jaytor said:

Thank you. I have read from other designers, and found from my own experience, that using a power supply that is oversized for the amplifier (or preamp) provides an improvement in sound quality, particularly in dynamics and less congestion when the music has a lot of mid bass. It's probably not a significant difference, but since the Purifi module can deliver 25 amps before the current limiter kicks in, I don't think that it is terribly overdesigned. I had originally planned on using a 1200VA transformer, but the 1500VA Audio Supreme transformer from Toroidy is the same size, so I decided to go with the larger capacity.

Good move. Much audio gear suffers, in subjective SQ terms, from inadequate power supply capability - the main reason for buying the most powerful power amp in the range of some manufacturer, is to try and overcome this inadequacy; it's a workaround for the fact that the design of the power supply is never as good as it should be. Unfortunately, too many designers use simplistic thinking, and measuring, to determine the quality needed in this area - and the consumer then loses.

14 hours ago, jaytor said:

The Neurochrome buffers are very neutral sounding with very low noise and distortion, but I'm wondering whether an input buffer that adds a little more character

What kind of pre-amp are you using? Maybe a tube pre-amp could provide some character. 
Where did you get does CRC modules?

@fas42 - yes, I agree. But commercial designers have to optimize performance for the cost and, while I believe that a high capacity power supply has definite SQ advantages, it’s not as clear that the improvements would justify the cost increase if building a commercial product - at least as far as I have taken it.
 

But since I only have to please myself, my general philosophy is to cram as much power supply into the box as I can make fit. 
 

@RickyV - I’m using a preamp I built myself. It uses a Khozmo stepped attenuator with an opamp output stage. I’m very pleased with the clarity and detail (it was a substantial improvement over my Parasound JC-2), but it is also fairly neutral sounding. I’m in the process of building another preamp which will use a fully discrete output stage with a high bias single ended class A output. 
 

I’ve had tube preamps in the past and the slow deterioration in SQ drove me nuts. I think I’ll be able to dial in the sound of the Purifi amps to my liking with a few more tweaks (or perhaps with just a bit more burnin). 
 

The power supplies for the high voltage rails are built using two Daisy chained universal power supply boards from the diyaudiostore. The low voltage supplies are built with two boards I bought from Jims Audio, again Daisy chained, but with resistors between the two boards since these boards aren’t designed with a CRC topology.  

5 hours ago, jaytor said:

@fas42 - yes, I agree. But commercial designers have to optimize performance for the cost and, while I believe that a high capacity power supply has definite SQ advantages, it’s not as clear that the improvements would justify the cost increase if building a commercial product - at least as far as I have taken it.
 

Unfortunately, the result is that most, especially older design amplifiers fail to deliver competent sound, when asked to deliver live sound levels. And audio consumers have learnt this, as being a trait of hifi systems - they're conditioned to expect the performance to degrade, as the volume increases - the "Get Out of Jail" card then used is to blame the speakers; when in fact they usually have nothing to do with it ...