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

[crenca]

Perhaps we can tack back to the point of this thread, and away from a high level debate about the relative design merits of class design, which are of course related but after 3 pages what is the question for Bruno?

 

I have a question but I think it is too broad so perhaps you folks can help me out.  It is an expeansion of what @firedog and @Em2016were asking on the first page.

 

Now that THD measurements have been driven so low, what else is Bruno hoping to achieve in this and future designs that relate to the unmeasured quality of the sound of Hi Fi amplification gear?  Not looking for a high level debate about measurements, but I am assuming that not everything related to SQ has been measured and/or is not seen in the standard measurements.  Instead, I am looking for a specific inteligible question for Bruno around this:  How do these new amps sound?  What is your goal around sound?  and the like...

 

 

[crenca]

16 minutes ago, psjug said:

It's bridged though.  Maybe it is simpler to look at the 286 which is not bridged.  But at lower power the issue is less severe I think.

 

2 minutes ago, Shadders said:

Hi,

OK - it is a chip amplifier - but the LM3886 specification states that the clipping voltage is about 4.5volts below 36volts. The specification from the integrators page states onset of clipping at 225watts into 8ohms, but the THD is 0.01% for 240watts into 8ohms. I think the integrators definition of clipping is different to the Texas Instruments definition.

 

Regards,

Shadders.

 

Gentleman,

 

What is the question for Bruno around all of this?!??

[crenca]

39 minutes ago, DuckToller said:

That's correct and he is an active part in this Q & A with Purifi.
Thank you for your question about smartfi. 

Lars Risbo - although he is more commonly known for the development of the TACT - Millennium Digital Amplifier & his work for TI - has been in the seat for the newly developed driver PTT6.5W04-01A , that offers a "breakthrough" in the optimization of "the various distortion mechanisms" which "translates into low intermodulation (IMD): clean, undistorted midrange even in the presence of a heavy bass."

I can just invite you to use this opportunity to find out more on the subject of long-stroke-drivers and "negligible" distortion. 

Best, Tom

 

Nice, some actual "marketing" that actually addresses real fundamental constraints/hurdles of transducer design on a technical level!

 

I particularly like that graph which shows the relative level of (in this case 2nd and 3rd order) distortion to the fundamental.  Makes one wonder about all the fretting we do around distortion in electronics (i.e. amps, dacs, etc.)...

 

 

 

[crenca]

4 hours ago, DuckToller said:

Thank you, Crenca,

would you like to extract your wondering into a phrase/questions for the Q &A?
Could be quite interesting to hear the opinion from industry experts on that subject!
Curious, Tom

 

I agree but I am the guy to form an intelligent question around this however.  I have read about the additive effects of the various distortions along the playback chain.  Perhaps a question would look something like:

 

"Have the various distortions (harmonic and non-harmonic) of modern amplifiers (when not being overdriven - at their "normal" playback levels) of all almost all designs become so low in level as to no longer being all that significant - in other words it's transducers, rooms, and recordings that are "responsible" for the "sound"?"

 

If the answer is "yes/possibly", coming back to my original question, what is responsible for the "sound" of a really (really really) clean amplifier like the 1ET400A as compared to a well regarded Class A/B, or even a well regarded Class A SS amp?  Using are ears, we all can tell the characteristic "sound" of these amps, so what accounts for this beyond harmonic/non-harmonic distortion measurements?

[crenca]

3 hours ago, Sagittarius said:

 

- Class D has achieved very low levels of distortion, but is it possible for class D amplifiers to continue their evolution into something close to a straight wire with gain, i.e. minimal phase shift in the audio band?

 

 

@Sagittarius, is this why some say that all class D amplifiers sound like music played through a DAC with a min phase filter selected?

[crenca]

40 minutes ago, barrows said:

 

Apparently the Mola Mola Kaluga monoblocks use a different type capacitor in the output filter which Bruno only describes as "monolithic"...

 

Ceramic capacitors maybe?

[crenca]

16 minutes ago, psjug said:

 

I wonder if his thinking has changed on this at all.  Here is what he said a couple years ago: https://www.soundandvision.com/content/bruno-putzeys-head-class-d

 

I was just as confused and as a result concocted a power DAC that directly converted DSD to analog in the power domain. The thought process that made me embark on this folly is a prime example of how not to start an engineering task but the result is still the most efficient (97 percent) and lowest distortion (0.007 percent) zero-feedback power amp ever made. Sonically, it was immediately killed by the first UcD prototype, which got me thinking. I decided that an aesthetic precept like “digital all the way” or “no feedback” can’t hold a candle to the simple question, “What problem are we trying to solve here?”

 

 

What exactly is the "power domain"?  A DAC's output is in the "power domain", in that it is a signal of such and such volts and current (though relatively low in output).  What is it about having the signal go through another amplification design and step that would lead (on almost wants to say necessarily) to a better subjective sonic output?  I assume the answer is that by breaking the problem into discrete steps the actual engineering works out better (better judged by subjective sonic output as well as cost, feasibility, etc.), but I wonder if Bruno could not expand on why this is.

[crenca]

4 hours ago, jabbr said:

 

I would thus add the question: "Since you've said that you like the SQ of your Class D as opposed to your own direct digital/power DAC ... why? What is the electrical correlate?"

 

This.

 

On the other hand, as near as I can tell (could be wrong) Bruno does not pretend to be a strict objectivist.  Comes back to a corollary to my question - what is it about the subjective SQ is Bruno after with these new designs as opposed to his previous efforts?  Certainly the answer is not "yet lower THD" or some such...that would be a side step of an answer 😉

[crenca]

3 hours ago, Shadders said:

Hi,

The specifications state that the voltage gain is 12.8dB (most power amplifiers have 26dB to 30dB). This is very low - to obtain the full output power, they indicate a 9.6volts (RMS) input signal (differential). It does not state whether this is a differential input, or single ended input to the power amplifier module.

 

For the non EE, what your talking about is an opamp between the input and the gain stage of the amplifer correct?  So input (typical 2v RMS single ended for example), then opamp with gain to 9.6v RMS, then the Purifi Class D gain stage, then speaker terminal outs...?