Purifi class-D amplifiers

[draki]

can't wait to see the midrange in it.

I don't know for sure, but over at gearslutz there was a tip that this is the midrange used: https://www.components-shop.com/prod...512R01-08.html

Nice driver, attached my measurement of it the other day (on a 23 x 37 cm baffled box - improvised with duct tape!), 50 cm on axis, scale 70 dB to show the 3rd HD.

I think there is a reason why its' grille is fixed!

[JonMarsh]

This part is available through Digikey, but not stocked; minimum order is 500 pieces, and it works out to about $18 each. Published data is very similar to what you've measured.

It's a stamped steel frame; designed for low cost in volume. Looks like a very good midrange for the money, the impedance plot hints at a motor with fairly decent distortion, and your measurements bear that out, though I'd hoped not to see the rise above 1 kHz due to inductivity modulation.

I'm not going to pose a group buy for $9K, though...

Unless there's 8 other guys that want $1K worth!!

:roflmao:

:laughat:

We don't have very big groups around here....


:coffee:

[JonMarsh]

I don't know for sure, but over at gearslutz there was a tip that this is the midrange used: https://www.components-shop.com/prod...512R01-08.html

Nice driver, attached my measurement of it the other day (on a 23 x 37 cm baffled box - improvised with duct tape!), 50 cm on axis, scale 70 dB to show the 3rd HD.

I think there is a reason why its' grille is fixed!

Where did you get a sample of this driver or buy it?

[draki]

Where did you get a sample of this driver or buy it?

Here:

https://www.toutlehautparleur.com/univers-des-marques/tymphany-peerless-vifa/grave-medium-pro.html

[draki]

though I'd hoped not to see the rise above 1 kHz due to inductivity modulation.

Well, considering its' cost, I think it is more than acceptable..... I do think this one has one of the highest price/quality ratios. Sitting hidden behind the Kii3 grille.

[Evil Twin]

The value proposition is quite clear...

[wkhanna]

I had dinner with Bill Hutchins, owner & designer of LKV Research while at Capital Audiofest back on Nov 1,2 &3.
his new class d amp was impressive, tho the choice of speakers he used this year held back the true capabilities.
he has high disdain for circuit topology utilizing feedback due to its intrinsic distortion in the upper frequencies.
especially since his forte is designing analog zero feedback phono pre-amps where just the slightest bit of noise or distortion is poison when stepping up from 0.5 millivolt to 2 volt.
he explained the class d allows him to use feedback since the current stays quite level in comparison over the audible upper frequency range.

quoted from Bill's website:
"Purifi Class D: The Purifi module embodies Bruno Putzeys latest (Patent Pending) advance in amplifier control circuitry. This innovation for the first time enables very high feedback to be maintained throughout the audio spectrum. As a result, the high frequency problems that have plagued all previous feedback amplifiers are banished. The complete audio spectrum can now be delivered to the speaker without degradation."

did he describe the technology to me as 'groundbreaking' when we were discussing it during dinner?
no.
more of a case of adding another capable tool in the box for designers to consider using.
to Bill's credit, he applies the feedback Very early in the signal path.

as the Maestro, Dr Marsh and our Dark Lord, Evil Twin are like to say:
"it is all in the application"

[Norm]

Interesting discussion, as is often the case in Mission Possible DIY. Regarding the Kii sub-discussion on the cost of drivers used keep in mind a couple of points. Each speaker has six drivers, six channels of DSP, D/A conversion and power amplification along with A/D conversion so both analog and digital inputs can be accommodated. The tooling and manufacturing setup costs for its enclosure look to me to be into 5 maybe 6 figures in dollars or euros. The software running on the DSPs is PHD level EE authorship. If this is to be a for profit enterprise all those BOM costs and overhead must be accommodated.

[ergo]

It is interesting that latest AudioXpress journal has a whole page add saying "Purifi first products available now"... wondering where ... or perhaps I should send an e-mail to sales.

[tktran]

Interesting discussion, as is often the case in Mission Possible DIY. Regarding the Kii sub-discussion on the cost of drivers used keep in mind a couple of points. Each speaker has six drivers, six channels of DSP, D/A conversion and power amplification along with A/D conversion so both analog and digital inputs can be accommodated. The tooling and manufacturing setup costs for its enclosure look to me to be into 5 maybe 6 figures in dollars or euros. The software running on the DSPs is PHD level EE authorship. If this is to be a for profit enterprise all those BOM costs and overhead must be accommodated.

I agree. We here audiophiles/tech nuts fawn over the latest and greatest driver technologies, but the commercial world has different ways to skin a cat.

For instance, in looking to see if my child's 2015 release digital piano could use dual voltage, I had to hunt down a service manual. Well looky here- its uses DSP for frequency AND phase response correction, as well 24bit AKM DACs and separate ADCs, and of course enough amplification for 2x3 way speakers.

For kicks I opened it up to take a look at the 6.5" driver in it- it looks like the ones we laugh about- stamped metal frame, small magnet, paper cone etc.

But I'd bet a lollipop the whole system measures flat as a pancak; but my point is it's not even mentioned anywhere in the advertising/marketing literature that it uses DSP/fully active/linear phase EQ.

This is from a reputable "real piano" manufacturer that's been making pianos for over 120 years, that's designed to be an instrument for learners for the FIVE years... but even professional/gigging musicians (our friends) or amateur musicians (my wife) are able to enjoy playing this as a real instrument...

[tktran]

It is interesting that latest AudioXpress journal has a whole page add saying "Purifi first products available now"... wondering where ... or perhaps I should send an e-mail to sales.

[ATTACH=CONFIG]29771[/ATTACH]

Please do and let us know

[Bear]

Looks like an embargo may have been lifted:

https://hificompass.com/en/reviews/purifi-audio-ptt65w04-01a-midwoofer

[ergo]

I got the answer to price inquiry very fast. It does state "still confidential until the web shop is up", so I'm not gonna copy them here. Anyone interested should be able to do their own inquiry.

I am very much considering going for the amplifier boards soon...

[Evil Twin]

I got the answer to price inquiry very fast. It does state "still confidential until the web shop is up", so I'm not gonna copy them here. Anyone interested should be able to do their own inquiry.

I am very much considering going for the amplifier boards soon...

This would be exactly what I need... one more fascinating project that I do not have time to work on...

As Jack Nicholson's character said in "As good as it gets",

"Go sell crazy somewhere else - We're all stocked up here!"

And this after recent news and new activities are cancelling my free time over the holidays...


What this means, is that I must resist... must not give in further to the Dark Side... no more parts for new projects I cannot work on!

[Bear]

What this means, is that I must resist... must not give in further to the Dark Side... no more parts for new projects I cannot work on!

What's one more TIE fighter in the hangar bay? They can't possibly be stolen by rebel infiltrators and used to blow-up a Star Destroyer or anything, right?

[Evil Twin]

What's one more TIE fighter in the hangar bay? They can't possibly be stolen by rebel infiltrators and used to blow-up a Star Destroyer or anything, right?

This one is strong in the Force, too... your logic is impeccable! It is merely the emotional pain of knowing there is so much unrealized potential awaiting future efforts...

That, plus some possible tool purchases lining up.

[ergo]

I have a bit more time, but less funds atm. So a problem is the other way around

We are pondering with my friend (who we built the OLA speaker project for) if we would buy Purifi modules for both of us or only for him for now.
The other point is a decision if to go for the EVM kit which includes "stereo front-end board (which has connectors and a configurable pre-gain stage)" or only the modules themselves. Latter is of course cheaper but would need some version of buffer still. I have balanced DAC-pre, but my friend has a single ended out on pre-amp. So balancing that signal would be needed. So thinking through the options there - even transformers as Jon considered in past, but the other way around - ie for balancing the SE signal coming in

[ILCCC]

Get one piece from a friend and will measure it by AP.

[ergo]

Similar progress... got the Eval kits and enclosure from Italy is waiting at office. Power supplies and connectors etc. should arrive next week as well.

ILCCC, what type of pre-stage/buffer you have for the module?

[Evil Twin]

Similar progress... got the Eval kits and enclosure from Italy is waiting at office. Power supplies and connectors etc. should arrive next week as well.

ILCCC, what type of pre-stage/buffer you have for the module?

[ATTACH=CONFIG]29781[/ATTACH]

Interesting... most interesting. I do not see that an online shop is open yet, so I would speculate that you arranged these through interaction with the sales email...

I have an urgent task still underway, but in a couple of weeks I may have some free time...

[ergo]

Yes - e-mailed the sales e-mail and got a price quote back in matter of hours. The modules shipped from Denmark.

PS. There is a good discount if buying 4 or 6 or ... If buying only 2 then getting the Eval kit makes sense at it is relative low addition to the full sum. I might attempt a custom buffer stage in future but the eval buffer will sure help get it up and running faster.

[ergo]

The rest of bits and pieces have arrived also. Will be seen if I can get them singing by Sunday evening. Some CNC work to be done to get all the holes done for the connectors and then the wiring etc.

[ergo]

Purifi amps initial phase complete and the modules are singing. Too early to commend on sound yet.

I created XLR socket holes for the potential upgrade with BPPBP - Bruno Putzey's Purist Balanced Preamp. That module has two XLR inputs and output.

I bought an extra 4mm front panel from HiFi 2000 and cut it down on band-saw to use as a separating wall between the power supply and amp.

The case is extra big to allow potential upgrade with "Integrated amp functionality and different buffer stage etc.

[ergo]

As I struggled with figuring out what exact wiring is needed to be done between Purifi EVK and the Hypex SMPS1200A400 I'll inlcude few photos that hopefully show enough.
(Note how 7 pin connector has last 3 connected on Purifi EVK end but a different pinout on SMPS end!

[dwk]

Looks like pricing is up on the site, finally. I'm pleasantly surprised - a bit of a premium over NC400, but in the same ballpark. I was honestly expecting something closer to 2x on initial rollout. I'm not sure I really have a use for one, but it's rather tempting.

[Evil Twin]

Interesting... most interesting... well worth additional investigation.

But given that time is the most precious resource, why can I never find a reliable Sith Apprentice when I need one?

[ergo]

I've been holding off posting the listening expressions as I wanted to be more sure if the first impressions stay and if it changes with some burn in.

As a comparison base I have a B&O ICEpower 200ASC based power amp and two NCore NC500MP based monoblocks
(NC500MP are the NCores with power supply and buffer integrated onto module - not the NC500OEM that would be a direct competitor)

Source has bee the Cambridge Audio Azur 851D and speakers the Wavecor Ardents EE edition

The first impression was that the Purifi sounded better in mids and highs. Even bit more clarity and precision in upper end. But at the same time the subjective feel was that the body of voices and music instruments seemed a bit thin. Like a speaker with baffle step compensation not quite there yet.

We listened with my friend and tried it also by bypassing the buffer and having 851D directly drive the Purifi. That had clear signs of trouble and the thinness remained while some more graininess emerged. Plus there is not enough gain in system anymore to play loud enough with some songs.

Anyhow - the solution I have for now is a Burson Soloist Headphone amp / preamp. As this one can drive the cans
Output power: 4W at 16 Ohms
Output impedance (Headphone Amp): 3 Ohm
Output impedance (Line Level): 30 Ohm
it was a good candidate to be a 'better pre stage' and the hope was that if it is the pre stage that matters for NC500OEM so much it can probably help here too.

And what it does is precisely what is needed in my system. The feel of 'missing body' and low end punch is now there and I would say now beats both the ICEpower and Ncore listed above. The mids and highs are also very much to my liking and there is more feel of 'darkness in between instruments' in lack of a better description.

My friend tried the Burson at his place with the OLA speakers we recently finished (he got the other Purifi EVK and built a replica just in a different enclosure). He had the same outcome for body and bass - meaning that the buffer in EVK kit lacks in these while running Burson with Purifi buffer bypassed. In his setup though he felt that Burson took away some of the top frequency sparkle. A bit too much for his liking... So the plan is to trial some pre/head amp DIY solutions. Nelson Pass's ACP+ preamp and WHAMMY headamp are two that we are thinking of trying.

I did not necessarily believe all the vendors selling NC500OEM amps that the buffer stage tweaking can have a huge effect. But I must say I do believe that now. I do find it interesting though as by datasheet the input impedance of the Purifi power modules is about 2.2kOhm. Which does not seem super challenging as even the opamps in the EVK should drive down to 600ohm ok probably.

****
Anyhow - what I have in plans and I've ordered part for is adding a 6800u Nichicon Audio series electrolytics close to the Purifi power module pins and also extra caps for the buffer stage pre and post the regulators. My thinking is that perhaps the power supply being still some 20+cm away (via wires) it might help create a better 'local energy reserve'. It's easy enough to try out and would be interesting.

I've been also thinking about Dynafrips Hestia or the Auralic Taurus Pre that is available as used.... but it seems too much cheating to take the easy way. More fun would be to experiment and do the buffers as DIY.
The Burson Soloist I have is not self build but is also modified - I replaced the power section with Jan Didden's SilentSwitcher, so it is half cheating

[MikePM]

Have you considered obtaining the Nord buffer boards that include two of either the Sparkos or Sonic Imagery Op Amps? I know Nord sells the boards as an upgrade for its NC500 based amp, and appears to be using them without modification on their purifi amp. The Nord One REV D Input Buffer Board is listed for 274.50 pounds sterling, so two of them would not be cheap, assuming they are compatible.

Also, has anyone used any of the Chinese amp chassis from Aliexpress. I would love to buy local, but there is limited selection, at least until someone builds a kit for these boards.

[Evil Twin]

Thank you Ergo for sharing your experience and comments with the board.

I have done brassboard experiments with different buffer circuits for the NC400 and NC500 several years ago, but due to various exigencies have not been able to follow up with fabrication.

The front end buffer seems to have impacts that are not easily revealed on the test bench- do not underestimate the difficulty of many preamps driving a 2k ohm load- while 600 ohm capability is often claimed, the listening experience that way can be most unsatisfactory. My own experience is that if one designs to drive a 75 ohm load robustly, then 600 ohm will sound quite "adequate". If one "designs" for 600 ohms, the results may not please...

Steve Manning is looking at a similar situation as he hopes to get an NCORE solution running in the not distant future. He has some options, with his Auralic Taurus Pre.

Just to whet your Dark Side Appetite, here is an interior picture of that preamp...




As the Dark Side encourages self torment as much as for others, I have ordered an Evaluation kit and cable sets, and compatible SMPS1200A400 power supply, along with some chassis components. Given the low likelihood of spare time for this in the next 3-6 months, this is more a down payment on the future and to have hardware on the shelf locally reproaching me for not being able to invest time.

But I did order some low dollar stand ins for my Halcro's, after finding some favorable pricing on a pair of Cambridge Edge W's.

[ergo]

A review of the Purifi amp + the kit speakers

https://audiophilestyle.com/ca/reviews/purifi-ptt65-woofer-and-1et400a-amplifier-technology-review-r866/

There is also a link in the article to the speaker kit box and Xover details

https://purifi-audio.com/wp-content/uploads/2019/12/SPK5-App-Note.pdf

Lots of interesting reading and details. No details on what is inside the amp box though - meaning no info what power supply and buffer was used. The reviewer seems perfectly happy with the sound balance and does not mention thin or missing body. So either it's down to taste or the box hides something different inside.... or then the speaker kit has been tuned with relative high baffle step compensation that will probably fix it too.

[wkhanna]

ergo,
the work you have done is very impressive.
alas, i do not deal in the world of milivolts or circuit design, i do know some folks who do.
Bill Hutchins is the designer for LKV Research.
i am certain he would be not only interested but actually excited to hear what you are doing, and lend some guidance based on what he has learned working with these types of amps.

if you decide to talk with Bill, let him know it was Billy Hanna, of Finley Audio, who referred you.
he will take great care with you if you let him know i sent you.

you can use the email or phone from the LKV site, or pm me for his private email.

[Evil Twin]

Have I qualified for the Purifi Club?

Documentary evidence-









and what I find to be incomplete documentation-

The EVAL1 manual provides the necessary information for connecting and controlling it.

But...


I have been expecting to see documentation about the 1ET400 pin interface and the application schematic- the component connectivity and a schematic for the Eval 1 would all be necessary to proceed with a proprietary development.

Is there something I have overlooked on the Purifi web site? Perhaps some one can point me in the right direction...

But so far I have seen no module data sheet and no schematics of the module board interface, not as provided commonly for Hypex Consumer or OEM module products- for which I have all information.

If some one could enlighten me, it would be most welcome... Google has not helped.

[ergo]

For EVK what is on the web seems all we get for now. I would also like to see the circuit diagram to perhaps try to mod it or at least be able to use the AUX stabilized supplies. I guess I can get them from opamp pins but would be better to find taps close to regulators instead.

For the 1ET400 I got an extended datasheet via e-mail after confirmed purchase. Not sure about the policy of publishing it, so I've sent a directed info beam towards "Location Coruscant" with it attached

[Evil Twin]

Received, decrypted and decoded.

Your assistance is fully appreciated. It seems that they are not going out of their way to make this easy for interested parties- reading between the lines, they seem to be interested in getting a lot of EVAL1 kits out for listening evaluations and online reviews producing favorable publicity, but are slow to release technical information that was readily forthcoming from Hypex.

Given the history involved, I would expect them to realize comparisons like this would be inevitable.

Regardless, my chassis parts have been shipped also, and should arrive before the end of the year.

Now, if only there were 8 days a week, like the old popular song by the Fab Four.

[Bear]

The web shop seems to be coming online, with the volume-sensitive pricing for the woofer shown. In quantities of 8+, that's ~$250/driver, which is pretty reasonable (4+ week lead time, though). So, when's the group buy?

[dwk]

The web shop seems to be coming online, with the volume-sensitive pricing for the woofer shown. In quantities of 8+, that's ~$250/driver, which is pretty reasonable (4+ week lead time, though). So, when's the group buy?

Does Purifi have anything on the site limiting resale (no warranty support etc)? If not, I have to imagine that there is going to be a very active group-buy/resale market for these - more than enough margin in the volume discount to cover costs and provide a substantial discount. I agree that at $250/driver they are significantly more attractive than at $400 - very attractive, actually.

[Bear]

Does Purifi have anything on the site limiting resale (no warranty support etc)? If not, I have to imagine that there is going to be a very active group-buy/resale market for these - more than enough margin in the volume discount to cover costs and provide a substantial discount. I agree that at $250/driver they are significantly more attractive than at $400 - very attractive, actually.

I can tell a story, and one that I'd need to confirm with their sales team, that they are handling things direct, but just don't want to sell pairs (order handling can be a non-trivial amount of work for a small company). I could be in for 3 - 5 of them, but I'd want some assurance that I'm not taking all of the risk for a manufacturing process that may need a few more kinks worked out.

[ergo]

While others are making sawdust I've switched to different mode

Plan is to see if providing a lot of drive current to Purifi modules will make them better and Passlabs design are on table as they have always known the benefits of lots of current... luckily here we only talk about pre amp class-A that will not fully kill the nice efficiency of the class-D power modules.

First one is an old design from Nelson Pass from 1997 - Balanzed line stage or Bride of the Son of Zen. I've always wanted to try a transistor pre with crazy high rail voltages and this one will be happy with the same +/-64V as the Purifi main supply. This should be closest sound wise to tube stage without actually using tubes


WHAMMY is from Wayne Colburn from Pass and is directed more as headphone amp, but it will sure have enough current. This one will allow playing with various dual op-amps available...


Last one is again from Nelson Pass but from 2019. Basically a JFET/MOSFET discrete gains stage with mostly 2nd harmonic distortion.


I also got 4x 6800uF caps to try out on main supply rails... not sure if the switching power supply will be happy to start with that 'powerbank' as a load. But I will try and see... perhaps it takes few attempts before it fully powers up but then it should run.


As my friend has the other Purifi kit we will have one that can run in stock Hypex PS + Purifi EVK buffers while we tweak the other one. That should keep us honest if we truly get benefit or just fool ourselves into thinking that every self made mod is a good one

[Evil Twin]

Interesting experiments, but I do see some likelihood of over current protection at startup unless the existing SMPS you’re using has a well managed soft start. There is only one reliable way to find out- on the bench

Your thinking about HV preamp drive is appropriate- I have pondered the idea of direct preamp output from my Benchmark HPA4 or even using the headphone drive...

But for now, my focus is elsewhere...

[ergo]

Fully understandable and a very good focus point that is too
In my neighborhood the temps start to drop below freezing and we had a few days of snow after Christmas and more to come for sure. So a cold garage is not the most inviting for woodworking at moment to a hot soldering iron with some class-A circuits and indoor activity is more inviting
Hopefully we'll make some progress that leads to someplace in end.

[Norm]

Ergo,

Is that the Hypex SMPS1200 Power Supply seen in your test rig above?

If the answer is 'yes' is it the model SMPS1200A100 or one of the higher voltage 'A180, 'A400 or 'A700? A few lunch hour minutes comparing Purifi vs. Hypex documentation it appears Purifi may have had this in mind as EVAL1 and Hypex SMPS1200, the connectors 'J1' on each look compatible. And for the lower voltage rails EVAL1's J3 pins 5 (+Vunreg), 6 (GND), and 7 (-Vunreg) getting power and ground from SMPS1200's J5 pins 3 (+Vaux), 5 (GND), and 7 (-Vaux).

One has to wonder at the human/business story of Hypex and Purifi. Launching a new company with evaluation boards that use a previous employer's and intended competitor's power supply module has to indicate the most amicable split imaginable OR a metric ton of nerve.

[ergo]

Yes it's the SMPS1200A

It took a bit of reading and pondering of both datasheets as for example Purifi one has -VP power while Hypex module output VDR-. Also the 7pin strip connector has a different sequence of powers/signal. This is why I added many photos of different angles... I was assuming that they will revise the EVK datasheet to make it easier for self builders as matching these two should be how most would use it. But this far that has not happened it seems.

***
As an update on my tweaking -

I have replaced the small caps on EVK module. Interestingly the originals were 22uF/63V type... but they are all in aux supply lines that come in at about 20V and then get stabilized to +/-12V. So I replaced all with Panasonic Fine Gold 220uF/25V

I also added the big 8200uF/80V ones for the main +/-60V supply. The SMPS has absoluttely no trouble starting up and there are no ill effects. Starts just as well as before.

I'm bringing the amp to my friends place tomorrow for A/B listening. He's Purifi + EVK is fully in stock form still. So I'll post listening impressions after that.

[Norm]

Ergo, thanks for the quick answer and information confirming the applicability of SMPS1200A.

FYI it appears NAD's first use of the Purifi amplifier tech was just announced at CES. The Master series M33 looks to be quite the 21st product.

https://darko.audio/2020/01/future-fi-at-ces-2020-the-nad-masters-m33/

[Evil Twin]

Ergo,



One has to wonder at the human/business story of Hypex and Purifi. Launching a new company with evaluation boards that use a previous employer's and intended competitor's power supply module has to indicate the most amicable split imaginable OR a metric ton of nerve.

Yes, Bruno may be strong in the Dark Side, too...

[Bear]

I got an email back from Claus regarding group buys. The most relevant part:

Warranty-wise you will be covered, however communication and shipping should got through the person on the original invoice.