Do No Negative Feedback Amplifiers Sound Better? - Page 3 - AVS | Home Theater Discussions And Reviews
Baselworld is only a few weeks away. Getting the latest news is easy, Click Here for info on how to join the Watchuseek.com newsletter list. Follow our team for updates featuring event coverage, new product unveilings, watch industry news & more!


Forum Jump: 
Reply
 
Thread Tools
post #61 of 70 Old 03-18-2014, 09:02 AM
RUR
Innocent Bystander
 
RUR's Avatar
 
Join Date: Feb 2007
Location: California Republic
Posts: 2,475
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 204 Post(s)
Liked: 107
RUR is offline  
Sponsored Links
Advertisement
 
post #62 of 70 Old 03-18-2014, 02:48 PM
 
SBruzonsky's Avatar
 
Join Date: Feb 2014
Location: Gilbert, Az
Posts: 239
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 16
Quote:
Originally Posted by RUR View Post

And PS Audio abandons Class D, altogether: http://www.psaudio.com/forum/#/discussion/6617/paul-makes-a-big-decision-on-the-amp

 

Yea, that's interesting.

 

I like and respect Paul McGowan of PS Audio. Heck, two of my review comments were used back in 2000 and 2007 for some magazine ads for the Power Plants!

 

Paul will be our speaker/exhibitor this Wed evening at our monthly Arizona AV Club meeting. I expect he will be demoing his new DSD upsampling DAC!

Mebbe he'll talk about the perils of his amplifier project?

 

Meanwhile, I am very, very happy that I have moved into the Theta Prometheus Class D w Analog Power Supply with BIG toroid. I have moved from  no "negative feedback" to having some, and I'm ok with that in view of what I am hearing!

SBruzonsky is offline  
post #63 of 70 Old 03-18-2014, 03:14 PM
AVS Special Member
 
edorr's Avatar
 
Join Date: Feb 2009
Posts: 2,469
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 41 Post(s)
Liked: 26
Quote:
Originally Posted by SBruzonsky View Post

Paul will be our speaker/exhibitor this Wed evening at our monthly Arizona AV Club meeting. I expect he will be demoing his new DSD upsampling DAC!

I ordered one of those (DirectStream DACs) for a shootout against my MSB. If it is as good +/- 5%, I'll sell my MSB and 2 x NAD M51, get three of them, and run MCH straight into this stack...
edorr is offline  
post #64 of 70 Old 08-02-2014, 08:38 PM
AVS Addicted Member
 
MichaelJHuman's Avatar
 
Join Date: Nov 2006
Location: Colorado Springs, CO
Posts: 19,016
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 262 Post(s)
Liked: 129
Wow, great thread. Does the Ultra hi end sub-forum attract people who can debate with civility? If this same thing had been posted to some other forums I know there would have been a flame-fest. Admittedly, it's more technical than most threads, but that doesn't stop people who lack knowledge from chiming in ( in my experience

"But this one goes up to 11"
MichaelJHuman is offline  
post #65 of 70 Old 03-08-2015, 09:18 AM - Thread Starter
AVS Addicted Member
 
Steve Bruzonsky's Avatar
 
Join Date: Jan 1999
Location: Gilbert, Arizona
Posts: 17,838
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 92 Post(s)
Liked: 30
Keep in mind this thread started back in 2007, prior to NCore 1200 modules being designed and available recently.

A recent interview with Bruno Putzsys, inventor of the NCore 1200 module used in the Theta Digital Prometheus monoblock. Very interesting.

http://ultraaudio.com/index.php/feat...audio-part-one

http://ultraaudio.com/index.php/feat...audio-part-two

Bruno explains his theory, proven objectively and subjectively, that traditional AB amplifiers generally have less negative feedback the higher the audio frequency, and engineers/designers must do workarounds/tuning to get the amplifers to measure and sound "good" to their taste; Bruno's theory for some years has been that if you add sufficient negative feedback to better equalize the negative feedback per the frequencies of the audio spectrum that this will sound "better" or like it should; that his latest NCore 1200 Class D modules add quite a bit more negative feedback than the earlier UCD Class D modules,
and with this higher negative feedback the audio sounds and measures objectively superbly; however, the NCore 1200 Class D modules are extremely susceptible to noise/electromagnetic interference, thus the power supply for the amplifier can be crucial in the resulting sonics of the NCore 1200 Class D modules.

The "fact" that myself and other Theta Digital Citadel 1.5 owners, a phenomenal traditional Class A monoblock, have switched over to the new Theta Prometheus NCore 1200 based monoblock shows that, as Bruno says, adding "massive" amounts of negative feedback can make the amplifier measure and sound better objectively and subjectively shows that "no negative feedback" (actually, this means much reduced negative feedback, which can't be completely eliminated) is a thing of the past at least for some amplifier manufacturers/designers, like David Reich/Theta Digital. However, apparently there is a cost in getting the power supply, whether analog linear or digital switched mode, right as NCore 1200 is at least in the high end audio field often very susceptible to electromagnetic noise and if only FCC standards are met there is still way too much noise which negatively affects the sonics.

Sure, there will still be new traditional Class AB amplifiers. And there will still be tube amplifiers. Audio is a very subjective creature. But there will be more
Class D NCore 1200 amplifiers for sure!

Please excuse me if my above discussion has errors as I am simply trying to give my own rudimentary understanding of what Bruno has discussed in great detail in his above interview.

You mean you don't remember me? Back 1999 - 2003, I started and moderated the AVS Tweaks forum and also the AVS Special Guests forum.

My home theater at:
http://www.avsforum.com/avs-vb/showthread.php?t=1158431
Steve Bruzonsky is offline  
post #66 of 70 Old 03-09-2015, 08:47 AM
AVS Special Member
 
Stereojeff's Avatar
 
Join Date: Oct 2000
Location: Whittier, CA USA
Posts: 1,547
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 35 Post(s)
Liked: 22
Required reading: Putzey's "The F Word"

http://linearaudio.nl/linearaudio.nl...olume_1_BP.pdf
Stereojeff is online now  
post #67 of 70 Old 03-09-2015, 10:20 AM
AVS Special Member
 
Glimmie's Avatar
 
Join Date: Sep 2000
Location: Los Angeles, CA
Posts: 8,206
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 300 Post(s)
Liked: 309
You need to keep in mind that a class D amplifier uses negative feedback in a very different manner to a class A/B amp. The issues of excessive feedback in a class A/B amp do not exist so much in class D. Bruno is trying to keep the technology dissertation simple here as the intricacies of negative feedback are not well understood in audiophile press.

One area that is very similar with feedback between class D and class A/B is output impedance. Though Bruno doesn't say, I suspect the high negative feedback he uses greatly helps to keep the output impedance low which in turn makes the output filter less frequency sensitive to the speaker load.

Yes, this is a good thing!

Glimmie's HT Page
Being redone - comming soon!


Last edited by Glimmie; 03-09-2015 at 10:28 AM.
Glimmie is online now  
post #68 of 70 Old 03-09-2015, 10:22 AM
AVS Special Member
 
Glimmie's Avatar
 
Join Date: Sep 2000
Location: Los Angeles, CA
Posts: 8,206
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 300 Post(s)
Liked: 309
Quote:
Originally Posted by Stereojeff View Post
Required reading: Putzey's "The F Word"

http://linearaudio.nl/linearaudio.nl...olume_1_BP.pdf
LOL, the engineering community has been saying this for years about audio amps but have always been shunned by the audiophile press.

Perhaps now they will listen to Bruno as he has a product they can't argue with!

BTW, I studied servo system design and I can tell you those equations Bruno shows really have nothing to do with audio per se. That math can be unilaterally applied to an audio amp or an auto pilot system on a plane. Same thing mathematically.

Glimmie's HT Page
Being redone - comming soon!


Last edited by Glimmie; 03-09-2015 at 10:31 AM.
Glimmie is online now  
post #69 of 70 Old 03-09-2015, 10:49 AM
AVS Addicted Member
 
amirm's Avatar
 
Join Date: Jan 2002
Location: Washington State
Posts: 18,818
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 1328 Post(s)
Liked: 731
As Glimmie says, class D amplifiers are entirely different beasts than traditional linear amplifiers. They can have hideous distortion products. Bruno's schtick has always been, "let that be distorted; I can fix it with feedback."

Let me give an example. Take power supply for the output stage of the amplifier. In linear designs, the power supply is almost always unregulated because it is far cheaper and more efficient to build it that way. The classic class AB amplifier has pretty high immunity to such high voltage fluctuations. Not so with class D. In a class D amplifier, the output is a series of pulses that clip at the supply voltage. What determines the analog output is the density of the pulses. That assumes that the pulse amplitudes are perfectly the same in each pulse. Change that, i.e. the power supply voltage, and now you have changed the analog output of the amplifier and with it, create a ton of distortion.

Another common problem is the handoff from one transistor to another. In class B amplifiers we bias the output creating a class AB where the two transistors both fight against each other but we eliminate crossover distortion. You can't do that in class D. Because each transistor is shooting up the supply voltage, if you let both conduct for any amount of time, they will create a dead short between the supply rails causing catastrophic failure. The solution is to have a timing gap. But now it means you have on purpose created crossover distortion.

You can either try to solve these problems fundamentally, e.g. having a highly regulated power supply, or let it be "bad" and then use negative feedback to fix the problem. If I were trying to build cost effective products, such as when Bruno worked for Philips I can understand such a bias. But when you build high-end products, I cringe at the thought of building a sloppy topology and then try to compensate with negative feedback. Negative feedback should be used for what you can't fix reasonably. Not as a fundamental operational tool.

Bruno in that interview says he has designed class D amps without negative feedback but then he built one with copious amount of negative feedback and it sounded better. Well, why not apply some amount of negative feedback to the former amp? Why all or nothing?

Let me finish by saying that Bruno has really made it his profession to understand and innovate in the area of class D amplification. His papers show very deep knowledge of the topic. So maybe he is just smarter than me and this is the best path forward .

Amir
Retired Technology Insider
Founder, Madrona Digital
"Insist on Quality Engineering"
amirm is offline  
post #70 of 70 Old 03-09-2015, 01:35 PM - Thread Starter
AVS Addicted Member
 
Steve Bruzonsky's Avatar
 
Join Date: Jan 1999
Location: Gilbert, Arizona
Posts: 17,838
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 92 Post(s)
Liked: 30
Quote:
Originally Posted by amirm View Post

Let me finish by saying that Bruno has really made it his profession to understand and innovate in the area of class D amplification. His papers show very deep knowledge of the topic. So maybe he is just smarter than me and this is the best path forward .
You are pretty darn smart. But as far as I am concerned, the Theta Digital Prometheus monoblock easily sounds better all around than Theta Digital's now discontinued Citadel 1.5 monoblock, as I sold my Citadels after demoing the Prometheus and got five of them!! If you demo these amps I think you will be quite surprised by how outstanding they sound! Subjectively I think Bruno really is onto something although I don't pretend to understand the engineering of it.

You mean you don't remember me? Back 1999 - 2003, I started and moderated the AVS Tweaks forum and also the AVS Special Guests forum.

My home theater at:
http://www.avsforum.com/avs-vb/showthread.php?t=1158431
Steve Bruzonsky is offline  
Sponsored Links
Advertisement
 
Reply Ultra Hi-End HT Gear ($20,000+)

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off