Are Class D Amplifiers really "digital"?

[sandyk]

From Silicon Chip magazine's Class D Amplifier.

[kumakuma]

10 hours ago, sandyk said:

From Silicon Chip magazine's Class D Amplifier.

 

Yes, the PWM waveform appears digital but the width of Vo will vary in an "analog" way. The non-digital nature of the waveform will be even more apparent when Vs is more complex than a sine wave.

[Miska]

I would say class-D amplifier can be more "analog" or "digital", depending on how the modulator works. If the modulator is analog, it is closer to analog one, although still switching PWM device. While one using digital modulator is essentially a "power DAC" and thus much closer to "digital".

 

[Miska]

On 9/13/2020 at 6:30 PM, kumakuma said:

Yes, the PWM waveform appears digital but the width of Vo will vary in an "analog" way. The non-digital nature of the waveform will be even more apparent when Vs is more complex than a sine wave.

 

Or you could say Vo works in a DSD'ish way...

[57gold]

Interesting (for pikers like me) interview with Michal of Mytek on development of his Class D amps after discussion of development of the company into Hi Fi from Pro Audio and their DACs in this article:

 

 

[davide256]

The topic is specious to me since a class D amp performs an analog task in the audio chain... the only thing that matters is whether it does it well.

Since the Bel Canto 600M's have received high praise for a number of years I'd have to assume the approach has merit when competently engineered.

And unlike class A or tubes wont roast you out of a smaller listening room 🙂

[Rexp]

'The only difference between analog and digital is the size of the sample rate. In the case of analog it is infinite, and for digital it is finite.'  Andreas Koch

[barrows]

5 hours ago, Rexp said:

'The only difference between analog and digital is the size of the sample rate. In the case of analog it is infinite, and for digital it is finite.'  Andreas Koch

Although I agree with Andreas' sentiment, in physical reality, even analog tape is granular at some level.  Everything in the cosmos is granular at some level: molecular, atomic, or quantum.  In that sense, there is actually nothing which is truly analog.

[firedog]

On 9/13/2020 at 7:11 AM, Rexp said:

Yes but the signal is off or on which is a definition of a digital signal. Analog signals are continuous. 

This is really another pointless audiophile debate that gets us nowhere.

But I agree with Paul M.: a PWM signal can be played back directly by analog equipment and produce sound. Poor quality sound, but sound. Therefore it is analog.

[Miska]

4 hours ago, firedog said:

This is really another pointless audiophile debate that gets us nowhere.

But I agree with Paul M.: a PWM signal can be played back directly by analog equipment and produce sound. Poor quality sound, but sound. Therefore it is analog.

 

Since DSD is essentially PWM, we can also conclude that DSD is analog.

 

[SoundAndMotion]

5 hours ago, Miska said:

 

Since DSD is essentially PWM, 

 

That's not true, as the video @kumakumalinked below and many web pages explain. DSD is PDM, pulse density modulation, and the way it's encoded and decoded is different from PWM, pulse width modulation. In some ways they look similar, especially with full scale simple sine waves, but they're not the same.

This OT post of mine doesn't answer the "analog-ness" though.

On 9/12/2020 at 4:59 PM, kumakuma said:

 

 

https://www.psaudio.com/pauls-posts/dsd-and-class-d/

 

 

 

[Miska]

13 minutes ago, SoundAndMotion said:

That's not true, as the video @kumakumalinked below and many web pages explain. DSD is PDM, pulse density modulation, and the way it's encoded and decoded is different from PWM, pulse width modulation. In some ways they look similar, especially with full scale simple sine waves, but they're not the same.

This OT post of mine doesn't answer the "analog-ness" though.

 

No, PWM is just a special cased version of PDM as Wikipedia also says. In practice all DSD is treated as PWM, because none of the converters transition state between subsequent samples of same value.

 

Essentially a DSD converter / PWM amplifier has no idea where the pulse train originates from, whether it originates from analog or digital modulator.

 

We've already demoed a "power DAC" amplifiers in Munich couple of times, based on my software modulators.

 

[SoundAndMotion]

Well, you sound like an engineer and I'm not, but I learned the distinction from engineering web sites, not Wikipedia. The difference between "similar" and "same" is semantic. Even the Wikipedia article you cite says:"For a 50% voltage with a resolution of 8-bits, a PWM waveform will turn on for 128 clock cycles and then off for the remaining 128 cycles. With PDM and the same clock rate the signal would alternate between on and off every other cycle. The average is 50% for both waveforms, but the PDM signal switches more often."

So the methods and ideas are related, but the implementation is different, i.e. the signals will be different, except at the peaks where they're the same. And several engineering/programming sites describe them as related, but different.

 

But you win.... to battle this out would be pedantic.

[Summit]

On 9/12/2020 at 1:04 AM, kumakuma said:

Recently one of our respected members expressed the opinion that Class D amplifiers couldn't be mentioned in this sub-forum because they are "digital".

 

Wikipedia seems to say that this isn't always true:

 

 

What are your thoughts on this?

 

The answer depends on what you mean by “really" digital.

[Miska]

1 hour ago, SoundAndMotion said:

So the methods and ideas are related, but the implementation is different, i.e. the signals will be different, except at the peaks where they're the same. And several engineering/programming sites describe them as related, but different.

 

Every modulator producing DSD output gives you different bit stream. Some are better, some are worse. Actually same for analog modulators too. So there's no one way to do things, modulators vary a lot.

 

So where I draw the distinction is whether the same pulse train / D/A conversion stage works or not.

 

[fas42]

4 hours ago, Summit said:

 

The answer depends on what you mean by “really" digital.

 

One could argue that a classic class AB topology is digital, if  it happened to use some processor chip within to dynamically vary the bias of the output stage so that it could work in something close to class A all the time - to nominally improve the subjective SQ. Digital processing is used to improve the numbers, or improve behaviour in a fault situation, etc; more and more these days - arguing over such semantics is pointless, these days.

[opus101]

9 hours ago, SoundAndMotion said:

 

But you win.... to battle this out would be pedantic.

 

'It is difficult to teach a man something when his salary depends on his not understanding it' - Upton Sinclair

[Miska]

On 9/15/2020 at 9:01 PM, SoundAndMotion said:

Even the Wikipedia article you cite says:"For a 50% voltage with a resolution of 8-bits, a PWM waveform will turn on for 128 clock cycles and then off for the remaining 128 cycles. With PDM and the same clock rate the signal would alternate between on and off every other cycle. The average is 50% for both waveforms, but the PDM signal switches more often."

 

Actually none of real modulators produce such output, or then the modulator is bad. Yes you can use 01010101 as a DSD silence pattern. As much as you can also use 01101001 or many other variations. But if you look for example output of my modulators, they don't produce either one for that case, but instead a random pattern.

 

[57gold]

Michal of Mytek waxes enthusiastically about GaN transistors and their capability to operate at much higher speed.  Since read that these are used in Merrill Audio's and Technics' new SOTA amp offerings.  Are amps incorporating these units the missing link in achieving "analog like" digital amps?  

 

Have not heard any of these and understand that Mytek will introduce high priced mono blocks with this technology.  Have seen some evidence of boutique builders with plans to introduce amps with mid fi pricing with GaN transistors.

[sandyk]

2 hours ago, 57gold said:

Michal of Mytek waxes enthusiastically about GaN transistors and their capability to operate at much higher speed.  Since read that these are used in Merrill Audio's and Technics' new SOTA amp offerings.  Are amps incorporating these units the missing link in achieving "analog like" digital amps?  

 

Have not heard any of these and understand that Mytek will introduce high priced mono blocks with this technology.  Have seen some evidence of boutique builders with plans to introduce amps with mid fi pricing with GaN transistors.

 

"The Merrill Element 118 monoblock amplifiers and the Merrill Audio Christine preamplifier are priced at $36,000 and $12,400 respectively. "

 They would want to be bloody good for those prices, wouldn't they ?  

[firedog]

3 hours ago, 57gold said:

Michal of Mytek waxes enthusiastically about GaN transistors and their capability to operate at much higher speed.  Since read that these are used in Merrill Audio's and Technics' new SOTA amp offerings.  Are amps incorporating these units the missing link in achieving "analog like" digital amps?  

 

Have not heard any of these and understand that Mytek will introduce high priced mono blocks with this technology.  Have seen some evidence of boutique builders with plans to introduce amps with mid fi pricing with GaN transistors.

I suggest you go back and find the article/interview about the new Purifi amps with Bruno Putzeys and partners. They explain why they don't think GAN is an advantage.

 

[57gold]

Thanks Firedog -  Read the article, comprehension was low on my part.  Understood that the positive aspects of GaN is offset by some negatives...so they didn't want to use them in their Purifi product.  

 

Wish they would develop a higher powered Purifi module, like 400 watts into 8 ohms.

 

Yes, sandyk, would hope the Merrill Audio stuff sound great for the freight.  A lot of "audiophile jewelry" in these new designs, casework, fancy footers, contrasting metal panels, high polish...in the pricing.  Give me a plain black box, and I'm good to go.  Though I would like it to be significantly smaller than the DNA-500 in my music room.

 

[firedog]

1 hour ago, 57gold said:

Thanks Firedog -  Read the article, comprehension was low on my part.  Understood that the positive aspects of GaN is offset by some negatives...so they didn't want to use them in their Purifi product.  

Their basic position seems to be that GAN also has disadvantages and they feel they can get superior results at a lower price point without it. At the very least, they are claiming it isn't the panacea that audiophiles assume it to be b/c of the high switching rate - that there are other factors involved in the end result.

Personally, seems to me like around $2-$3K can get you a very well made dual mono/stereo Purifi amp with a nice case. Not audiophile bling, but certainly quite respectable. If you are OK with Class D, that's probably all you need for today's state of the art.

 

I assume at some point they will make more models of the amp module if it is successful. Those wanting really high power can get an NCore 1200 based amp.

[barrows]

1 hour ago, 57gold said:

Thanks Firedog -  Read the article, comprehension was low on my part.  Understood that the positive aspects of GaN is offset by some negatives...so they didn't want to use them in their Purifi product.  

 

Wish they would develop a higher powered Purifi module, like 400 watts into 8 ohms.

 

Yes, sandyk, would hope the Merrill Audio stuff sound great for the freight.  A lot of "audiophile jewelry" in these new designs, casework, fancy footers, contrasting metal panels, high polish...in the pricing.  Give me a plain black box, and I'm good to go.  Though I would like it to be significantly smaller than the DNA-500 in my music room.

 

I do not mean to criticize the newer amplifiers from Merrill, and I have not heard them, so i do not know how they sound.  But their published specifications are quite a bit worse than those of well implemented amplifiers using Ncore or Purifi modules, so there is that curiousity: if GaN was so much better, would we not expect GaN based amps to have at least equal distortion and noise specifications as Ncore and Purifi?

Mr. Putzeys has stated that it is the plan to produce more powerful Purifi modules, I am sure they are just waiting a bit for sales to offset some of their development costs before they can introduce more products.

[57gold]

2 hours ago, barrows said:

Mr. Putzeys has stated that it is the plan to produce more powerful Purifi modules, I am sure they are just waiting a bit for sales to offset some of their development costs before they can introduce more products.

 

Thanks, thought I read that somewhere. 

 

Some one like Nord or Apollon or... will make a nice sounding, reasonably priced higher powered Purifi based amp when the new units are available.