Are Class D Amplifiers really "digital"?

[firedog]

53 minutes ago, 57gold said:

 

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. 

At some of the other sites, it seems the Apollon and the March Audio are considered the better built/layout of the "reasonably priced" models.

[DuckToller]

4 hours ago, 57gold said:

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.

afaik,

they are alrady available in different configurations (single power, dual mono, mono blocks, buffers/OP amps) with Nord, Apollon and Audiophonics in Europe as example. 
I've read VTV in the US do have the most price sensitive offer for stereo, while the Nord mono blocks are quite interesting given the low  £ - Sterling exchange rate at the moment. 
For the GaN, Orchard offers a competitive priced product which had quite a good review from Audio Xpress lately (compared it to PuRiFi).
Cheers, Tom

[57gold]

Another GAN amp in the works for $3K:

 

https://www.underwoodhifi.com/products/lsa-electronics

 

[RickyV]

https://agdproduction.com

[semente]

On 9/15/2020 at 1:49 AM, 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

 

I suggest this two-part piece by Jim Lesurf:

 

Good Resolutions

 

If you tend to read a variety of audio magazines then you sometimes encounter statements like

 

· “Analog systems like LP have infinite resolution and can reproduce infinitesimally tiny details of the audio.”

 

· “Digital systems like audio CD (CD-A) have a level of distortion that rises when the audio signal level falls below about -60dBFS.”

 

If true, these statements mean that LP has a greater ability to record and replay details than CD-A.

This would be quite significant.

So what do the above statements mean, and are they accurate?

 

http://www.audiomisc.co.uk/HFN/goodresolutions/page1.html

 

http://www.audiomisc.co.uk/HFN/goodresolutions/page2.html

 

 

[semente]

On 9/15/2020 at 8:07 PM, Miska said:

 

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.

 

 

What about FM broadcast? Is it digital or analogue (or both)?

[Miska]

4 hours ago, semente said:

What about FM broadcast? Is it digital or analogue (or both)?

 

I would guess most of the transmitters are digital these days, possibly using some sort of SDR (Software Defined Radio).

 

The more complex modulations like QAM256 used for DVB and mobile networks are always digital creation.

 

By the way Technics also just recently announced a digital class-D amp using GaN FETs:

https://www.technics.com/uk/news/414/index.html

 

[asdf1000]

1 hour ago, Miska said:

By the way Technics also just recently announced a digital class-D amp using GaN FETs:

https://www.technics.com/uk/news/414/index.html

 

We need to see the switching freq at DSD256 rates (12MHz) !

One day 🙂

 

 

[barrows]

2 hours ago, asdf1000 said:

We need to see the switching freq at DSD256 rates (12MHz) !

One day 🙂

So far, I do not agree with this sentiment.  I have been working with the Purifi class D modules here, trying to get the best out of them.  So far they are on par, or sounding better than, any amplifiers I have heard here.  The only amp which has come close (and could be considered preferable, maybe, in some areas), has been the Bricasti M-25, which is a $20K component.  And I am still making improvements to my Purifi amp build.  As far as I can tell, the Purifi modules themselves are as near "perfect" output stage as exists.  Getting the best out of them requires designing and implementing the best input stage, power supplies, layout and wiring, as their performance appears to be limited only by the implementation.

So far, the GaN amplifiers which are available, have worse measured performance than the Purifi demo set up: so I do not see a real world advantage for higher switching frequencies, at least yet, no one has produced a GaN amp which actually shows an improvement in performance.

To those who seem to think higher switching rates are going to result in better class D amp performance, where are the numbers to back up this assertion, I have not seen any.

[57gold]

barrows, have you seen this fellows assault on implementing the Purifi modules with 3 transformers for LPSs for driver, input and output stages, Class A discrete input stage?

 

 https://lkvresearch.com/lkv-veros-power-plus.html

 

Be interested to hear of the choices you make as you work on yours.

[Miska]

8 hours ago, barrows said:

So far, I do not agree with this sentiment.  I have been working with the Purifi class D modules here, trying to get the best out of them.  So far they are on par, or sounding better than, any amplifiers I have heard here.  The only amp which has come close (and could be considered preferable, maybe, in some areas), has been the Bricasti M-25, which is a $20K component.  And I am still making improvements to my Purifi amp build.  As far as I can tell, the Purifi modules themselves are as near "perfect" output stage as exists.  Getting the best out of them requires designing and implementing the best input stage, power supplies, layout and wiring, as their performance appears to be limited only by the implementation.

So far, the GaN amplifiers which are available, have worse measured performance than the Purifi demo set up: so I do not see a real world advantage for higher switching frequencies, at least yet, no one has produced a GaN amp which actually shows an improvement in performance.

To those who seem to think higher switching rates are going to result in better class D amp performance, where are the numbers to back up this assertion, I have not seen any.

 

For example most low-rate switching amps I've seen so far have issue that the bandwidth (flat frequency response) doesn't cover entire spectrum of hires material - that is 100 kHz. In addition they have aliasing problems in presence of high frequency content.

 

Another challenge is still how much ultrasonic noise they put out because the distance between the noise and the audio signals is so small that it is hard to make a simple efficient low impedance output filter.

 

I guess Purifi doesn't go flat to 100+ kHz bandwidth either?

 

[sandyk]

3 hours ago, Miska said:

I guess Purifi doesn't go flat to 100+ kHz bandwidth either?

This isn't restricted to Digital amplifiers either, with many Analogue amplifiers having an Input filter well below the actual capabilities of many of them.

[57gold]

Miska - Lots of specs on this site, graphs and charts that seem to address Purifi capabilities. Don't really understand the practical implications of them, but I'm pretty sure you do.  

 

https://purifi-audio.com/eigentakt/

 

Looks like frequency response rolls off above about 60kHz.  Been led to believe that most speakers are built to reproduce up to 20 -25kHz? And that most folks can't hear airborne sound above that level.

[sandyk]

2 hours ago, 57gold said:

Looks like frequency response rolls off above about 60kHz.  Been led to believe that most speakers are built to reproduce up to 20 -25kHz? And that most folks can't hear airborne sound above that level.

According to that reasoning, then anything greater than 24 bit 48kHZ, including 24/96, 24/192, SACD and DSD is a waste of time ,yet many prefer SACD with it's 50kHz capabilities over RBCD 's 16/44.1kHz, with many also appearing to prefer higher resolution DSD over SACD.

[57gold]

Personally, I do not understand how format relates to frequency response, nor most of the discussions here on digital technology and audio circuits.  Last science I took was Chemistry in high school, not AP like my 3 kids (their mother's family has multiple PhDs in sciences).  Never took Physics, took 2 history classes as a senior, flexible curriculum.  

 

So I was careful to say "was led to believe" in making my comment...which involved no reasoning.  An example of why I may have been led to believe this would be by looking at the specs on speakers.  Well regarded by some Wilson Audio speakers, their $38K Sasha has these specs for frequency response, "20Hz–30kHz ±3dB". To a piker like me, sounds like that's the range, plus a little, that folks care about hearing?

[sandyk]

8 hours ago, 57gold said:

Personally, I do not understand how format relates to frequency response, nor most of the discussions here on digital technology and audio circuits.  Last science I took was Chemistry in high school, not AP like my 3 kids (their mother's family has multiple PhDs in sciences).  Never took Physics, took 2 history classes as a senior, flexible curriculum.  

 

So I was careful to say "was led to believe" in making my comment...which involved no reasoning.  An example of why I may have been led to believe this would be by looking at the specs on speakers.  Well regarded by some Wilson Audio speakers, their $38K Sasha has these specs for frequency response, "20Hz–30kHz ±3dB". To a piker like me, sounds like that's the range, plus a little, that folks care about hearing?

 Perhaps it's also about the rise and fall times of the envelope in the audible frequency range ?

I also get an improved performance from headphones such as the ATH M70x which have an extended  response of sorts from 5 to 40,000Hz. 

[Miska]

On 9/27/2020 at 5:46 AM, sandyk said:

This isn't restricted to Digital amplifiers either, with many Analogue amplifiers having an Input filter well below the actual capabilities of many of them.

 

Mostly Naim comes to mind, but same applies to their digital gear. Hires frequency range is just cut off.

 

Many amps have input filter with something like 1st order RC filter with -3 dB point at 100 kHz.

 

[Qhwoeprktiyns]

On 9/26/2020 at 5:16 PM, barrows said:

So far, I do not agree with this sentiment.  I have been working with the Purifi class D modules here, trying to get the best out of them.  So far they are on par, or sounding better than, any amplifiers I have heard here.  The only amp which has come close (and could be considered preferable, maybe, in some areas), has been the Bricasti M-25, which is a $20K component.  And I am still making improvements to my Purifi amp build.  As far as I can tell, the Purifi modules themselves are as near "perfect" output stage as exists.  Getting the best out of them requires designing and implementing the best input stage, power supplies, layout and wiring, as their performance appears to be limited only by the implementation.

So far, the GaN amplifiers which are available, have worse measured performance than the Purifi demo set up: so I do not see a real world advantage for higher switching frequencies, at least yet, no one has produced a GaN amp which actually shows an improvement in performance.

To those who seem to think higher switching rates are going to result in better class D amp performance, where are the numbers to back up this assertion, I have not seen any.

 

Do you have any recommendations for well implemented  purifi amps (not DIY) amps? I am curious to test Purifi but there are so many offered now I have no idea which stand out. Thanks. 

[DuckToller]

1 hour ago, hopkins said:

 

Do you have any recommendations for well implemented  purifi amps (not DIY) amps? I am curious to test Purifi but there are so many offered now I have no idea which stand out. Thanks. 

Audiophonics, Nord Acoustics UK, Appollon Audio come to mind . .

Cheers Tom

[w1000i]

On 9/26/2020 at 6:16 PM, barrows said:

So far, I do not agree with this sentiment.  I have been working with the Purifi class D modules here, trying to get the best out of them.  So far they are on par, or sounding better than, any amplifiers I have heard here.  The only amp which has come close (and could be considered preferable, maybe, in some areas), has been the Bricasti M-25, which is a $20K component.  And I am still making improvements to my Purifi amp build.  As far as I can tell, the Purifi modules themselves are as near "perfect" output stage as exists.  Getting the best out of them requires designing and implementing the best input stage, power supplies, layout and wiring, as their performance appears to be limited only by the implementation.

So far, the GaN amplifiers which are available, have worse measured performance than the Purifi demo set up: so I do not see a real world advantage for higher switching frequencies, at least yet, no one has produced a GaN amp which actually shows an improvement in performance.

To those who seem to think higher switching rates are going to result in better class D amp performance, where are the numbers to back up this assertion, I have not seen any.

Have you heard any technics amplifers, Panasonic is serious about developing there amps with GaN.

https://www.technics.com/us/news/20200901-su-r1000/index.html

[barrows]

As I build my own amps, I have not really spent a lot of time paying attention to the amps that are available with Purifi modules.  A lot of the offerings, from say, Nord et al, appear to have less than ideal internal layouts for some weird reason.  I do like the options which allow for the pro audio style discrete opamps, the pro audio discrete opamps from Weiss, for example, are very, very good.  How much does all this matter, I do not know, but I prefer an amp with a logical and well sorted internal layout.

[w1000i]

6 minutes ago, barrows said:

As I build my own amps, I have not really spent a lot of time paying attention to the amps that are available with Purifi modules.  A lot of the offerings, from say, Nord et al, appear to have less than ideal internal layouts for some weird reason.  I do like the options which allow for the pro audio style discrete opamps, the pro audio discrete opamps from Weiss, for example, are very, very good.  How much does all this matter, I do not know, but I prefer an amp with a logical and well sorted internal layout.

If possible can you share your layout and what are you trying to optimize ?  Can someone upgrade the board with copper lines or modified the parts on the bords.

[barrows]

Just common sense stuff, keep the AC input wires away from the rest of the circuitry, keep the input (XLR) and output (speaker) wire short and tight.  Keep the high voltage part of the power supplies away from the output modules.  My build features a separate custom linear power supply for the input stage and modulator section of the amplifier.   As to mods there are million things one could try, but I would advise starting with a simple set up, to have a good baseline for performance, and then try things from there.  This is an early pic of my build.  I have since changed the speaker output wiring to two wires per binding post, allowing for tighter.shorter loop and better connections.  And the wiring to the left rear of the chassis (temporary) has been cleaned up, shortened, and the switch to the front panel is enabled to take the amp in and out of standby mode.

 

[57gold]

barrows - How are you liking the Purifi amp build?  

 

So, instead of a third party, discrete input, you are powering the "built in" driver with an LPS?

 

[barrows]

The Purifi amp is great.  I power the input board section with a custom linear power supply, this powers the input opamps, and the modulator circuitry of the Purifi modules.  I am liking this amp as is, with the Purifi Eval board as the input gain stage.  I will probably eventually try different input stages a well, as I suspect there could be improvements there, maybe...