Questions For Interview With Bruno Putzeys & Lars Risbo About Purifi Audio

[The Computer Audiophile]

Hi Guys - The team at Purifi has agreed to do a Q&A with the Audiophile Style community. This technology looks really good and I'm very excited to host such a Q&A.

 

Please ask questions below in this thread for us to compile and deliver to Bruno Putzeys and Lars Risbo. 

 

If Purifi is new to you, please read Tom's recent article about the company and technology here:

 

 

[firedog]

Do you  believe this technology to sound superior to NCore boards such as the NC400, 500, and 1200? 
If so, why?

[Matias]

Will the Purify modules be pin compatible with their competitors for easy swap of modules?

 

What other power ratings are they planning to release?

 

Also planning all in one modules (power supply + buffer + power stage)?

 

Are Purify only developing parts or they plan to release entire products like active speakers?

 

DACs coming too?

[Ralf11]

ask about Gallium

 

--->  see if there is a heavy silence...

[Matias]

5 hours ago, firedog said:

Do you  believe this technology to sound superior to NCore boards such as the NC400, 500, and 1200? 
If so, why?

He already answered this on the 6moons interview. Sonically and measurements are quite a step up from ncore.

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

[Nordkapp]

Besides NAD, what manufacturers have commited to and/or expressed serious interest? 

[Matias]

Any improvements on the switching power supplies as well?

 

Other drivers (tweeters, woofers) also planned?

[Rt66indierock]

Will there be a reference amplifier design for the DIY market?

[fas42]

What sort of testing was done to ensure that the units are intrinsically resistant to interference, noise factors? That is, how much work needs to be done by implementers to fully shield the modules from anomalies in their electrical environment?

[mocenigo]

3 hours ago, Ralf11 said:

ask about Gallium

 

--->  see if there is a heavy silence...

 

GaN? I think Bruno Putzeys already said the Eigentakt modules are not GaN.

[Matias]

1 hour ago, mocenigo said:

 

GaN? I think Bruno Putzeys already said the Eigentakt modules are not GaN.

Still the question is good.

What does he think of GaN? Will there be future Purifier modules using it? Why did he not use it yet?

[asdf1000]

Hi @The Computer Audiophile

 

I've seen comments across the internets (these are not my thoughts) that the switching frequency is the only 'issue' with Class D - one argument is it's not currently high enough with Hypex and ICE designs and this then needs aggressive filtering that can affect the treble performance making everything sounds smooth and warm.

 

Are there merits to pushing this switching noise higher and higher, to make filtering easier? Some say it needs to go to 5 MHz and beyond to make filtering easy without affecting the top end, again making everything sound warm and smooth... again these are not my thoughts, just what I've read over the years.

 

And what's the switching frequency with this Purifi amp project

 

Would love Bruno's thoughts on these (I've seen all the discussion on both sides so let's not get into it here).

[asdf1000]

The following question might initially come across as rude but believe me it's not intended to be rude.

 

If Bruno solved Class D distortion issues within 2 hours, with "no distortion at all, for every reasonable definition of “none at all.”, then what's the point of this Purifi project.

 

How can you have less distortion than "no distortion at all" ? So , what is this Purifi project trying to do better?

 

It might be a great opportunity for him to settle (clarify) all the technical arguments people throw out against Class D. Maybe

 

 

 

https://www.soundandvision.com/content/bruno-putzeys-head-class-d

 

 

[Ralf11]

1 hour ago, Matias said:

Still the question is good.

What does he think of GaN? Will there be future Purifier modules using it? Why did he not use it yet?

 

 

Exactly.  I bet he is thinking forward by many years or more...

[phosphorein]

25 minutes ago, Ralf11 said:

 

 

Exactly.  I bet he is thinking forward by many years or more...

 

Possibly he has some concern about noise as GaN is somewhat noisier than GaAs.

 

[fas42]

Which brings up another question: how effective is the output filtering at completely removing all non-audio frequencies; compared to earlier versions of that technology?

[maty]

A year ago I opened a thread in the diyaudio forums asking about the phase shift in class D technology and its influence on the sound and I still do not know the answer.

 

In class A and AB technology, this shift is less than 6 degrees at 20 kHz, which almost nobody specifies. But in class D it is much higher!  There is a new module, IcePower 1200AS2 that reaches up to 70 degrees!!!

Phase shift in class D amplifiers. How it affects the sound?

 

Specially with acoustic instruments and "natural" voices (without autotune, vade retro satana).

I take the opportunity to raise the issue directly, thank you very much from Spain.

[maty]

Second question.

 

Yesterday I read a very interesting article wrote by Bob Katz a year ago.

 

https://www.innerfidelity.com/content/katzs-corner-episode-25-adventures-distortion

 

Quote

In today's investigation I aim to get a handle on how to use distortion to improve the sound quality of our playback gear. Yes, I said "improve", because we're going to redistribute the harmonic emphasis of our signal chain. Not all amplifiers with ultra-low distortion sound harsh or small: Notable among good sounding (or at least sonically neutral) low-distortion amplifiers is the Hypex Class D amplifier, invented by Bruno Putseyz. His recent model, the Hypex NCore, has near zero harmonic distortion and is audibly close to the proverbial straight wire with gain.

 

No distortion sounds better than a little bit of bad distortion, but moderate, well-distributed distortion sounds better, too!. I believe there's a middle amount where distortion can sound deadly. Why? Because in that middle area, where the overall distortion measures somewhat low, but not close enough to zero, the presence of some higher harmonics can psychoacoustically predominate over the important lower ones. In other words, the distribution of the distortion is the key to sonic differences.

 

What do you think about predominant H2 and other decreasing monotonous harmonics? To enjoy the music at home.

 

[IMG, link] http://maty.galeon.com/WP-imagenes/hum/xrk971-Alpha-20-2.87vrms-8ohms-FFT.png

 

[Shadders]

1 hour ago, maty said:

A year ago I opened a thread in the diyaudio forums asking about the phase shift in class D technology and its influence on the sound and I still do not know the answer.

 

In class A and AB technology, this shift is less than 6 degrees at 20 kHz, which almost nobody specifies. But in class D it is much higher!  There is a new module, IcePower 1200AS2 that reaches up to 70 degrees!!!

Phase shift in class D amplifiers. How it affects the sound?

 

Specially with acoustic instruments and "natural" voices (without autotune, vade retro satana).

I take the opportunity to raise the issue directly, thank you very much from Spain.

Hi,

This is important. It seems that class D amplifiers despite amplifying, are acting like non-linear filters too.

 

Sounds like a job for MQA Ltd........

 

Sadly, they would require a separate MQA file that is optimised for every class D design.

 

Regards,

Shadders.

[Shadders]

9 hours ago, mocenigo said:

 

GaN? I think Bruno Putzeys already said the Eigentakt modules are not GaN.

Hi,

As per article below :

https://semiengineering.com/electric-cars-gain-traction-but-challenges-remain/

 

The use of GaN and Silicon Carbide MOSFET's increases efficiency due to their faster switching speeds. Higher switching speeds can reduce the dead time, so maybe this is a future enhancement ?

 

Regards,

Shadders.

[mocenigo]

Very interesting article, but I do not see the connection between GaN and electric cars 🙂

 

34 minutes ago, Shadders said:

Hi,

As per article below :

https://semiengineering.com/electric-cars-gain-traction-but-challenges-remain/

 

The use of GaN and Silicon Carbide MOSFET's increases efficiency due to their faster switching speeds. Higher switching speeds can reduce the dead time, so maybe this is a future enhancement ?

 

Regards,

Shadders.

 

[Shadders]

Just now, mocenigo said:

Very interesting article, but I do not see the connection between GaN and electric cars 🙂

 

 

Hi,

Electric cars are investing in GaN and SiC mosfets which offer higher switching speeds - more efficient. The class D modules can do this too - use higher switching speed devices.

 

Regards,

Shadders.

[mocenigo]

Yes and no. Class D amps have a phase rotation that is a linear function of the frequency. This is just a delay. So in fact this is often much better than irregular phase rotations as in A and AB amps. Luckily, the rotation of the latter are much more contained.

 

NCore also has much smaller rotations than ICEpower and, it seems, ICEEdge - I expect the same for Eigentakt

 

Still, it would be VERY INTERESTING to hear Putzeys take on the matter.

 

 Roberto 

 

59 minutes ago, Shadders said:

Hi,

This is important. It seems that class D amplifiers despite amplifying, are acting like non-linear filters too.

 

Sounds like a job for MQA Ltd........

 

Sadly, they would require a separate MQA file that is optimised for every class D design.

 

Regards,

Shadders.

 

[mocenigo]

2 minutes ago, Shadders said:

Hi,

Electric cars are investing in GaN and SiC mosfets which offer higher switching speeds - more efficient. The class D modules can do this too - use higher switching speed devices.

 

Regards,

Shadders.

 

Yes, I meant between this and audio, sorry.

 

The higher switching speeds and the corresponding shorter dead times would be a big plus for audio. But for the moment they are noisier, IIRC. Now, at a switching speed of 500khz you get about 5 bits of depth at 20Khz and 6 at 10Khz which is beyond what one can hear (even a very very young person) so the signal as perceived by the brain is already perfect. What higher switching speeds could improve is timing, and it is already quite precise.

 

 Roberto 

 

[Shadders]

6 minutes ago, mocenigo said:

Yes and no. Class D amps have a phase rotation that is a linear function of the frequency. This is just a delay. So in fact this is often much better than irregular phase rotations as in A and AB amps. Luckily, the rotation of the latter are much more contained.

 

NCore also has much smaller rotations than ICEpower and, it seems, ICEEdge - I expect the same for Eigentakt

 

Hi,

Please see the screenshot of a simple class AB amplifier group delay.

Despite the minimal group delay below 50Hz, the graph shows that the group delay is constant. The group delay is the dotted line at the bottom of the graph.

 

Can you provide your examples of class A or class A/B amplifiers with irregular phase rotations ? Thanks.

 

Regards,

Shadders.