Negative Feedback a deal killer?

I don't know, my memory seems to be departing and I can't get it back for love nor money. A good article on Chaos is in the book on modern physics edited by Paul Davies, "What Is Chaos That We Should Be Mindful Of It?". Maybe on the web for all I know.

Hello Unsound,

I think that H2Oaudio has the full right to participate as a "private user". The reason is that he is not a designer but a person who buys mass production B&W Icepower module and installs them in his chassis (I bet makes some modifications too) and place the label "H2O" on it. Incidently ihe same is with Bel Canto, Wyred4Sound, D-Sonic and bazzilion of others buyers of ICEpower modules.

The single exception, IMO, is Jeff Rowland who while uses B&W modules yet developed his own highly sophisticated power supply and with PFC at it. My hat off to him!

Athmosphere designed his equipment form A to Z and his post is 100% accurate. He is particualrly right in: " It has also been shown that feedback, due to the time delay, actually **increases** certain distortions, namely the 5th 7th and 9th harmonics."

In his 2nd post he acknowldge that "The faster the amplifier, the less this is a problem!" He correctly noted that "... faster is not the same as 'real time' " and he is right here as well - otherwise Spectron for example would list its distortion level as zero which they are not (but very small and even order of magnitude smaller in their monoblocks but its different mechanism in force).

Also, you are mistaken, not all class D amplifiers use the same fast negative feedback as you believe. Spectron explains its method on its web-site but, for example, Bruno Putzeys (formerly of Philips) uses exactly the opposite approach and his powerful class D amplifiers (under "Kharma" name) while expensive at $25k - $30k, are said to be excellent.

Regarding what H2Oaudio wrote in relation to the capabilities of Spectron amplifiers - I copied his post and e-mailed it to them. If they want they will answer.

I believe that B&O recommends to the users of their Icepower modules not to apply them to the loads below 2 Ohms - at least until very recently so I can understand this concern... Surely, Athmosphere amplifiers, particularly since he explained the "badness" of negative feedback, cam drive such loads with ease....otherwise I will start to believe that even Athpmosphere designs are not "perfect" and he is only human ... :--) :--):--)

Cheers, life is gorgeous!

I think our ears are the best test instrument.

Unsound - As I understand it class D doesn't need a lot of negative feedback since duty cycle is much more linear than transistor voltage in class AB output stage*. In addition it has inherent low output impedance since speaker is always connected to zero source impedance (GND, VCC) with very low resistance Mosfets. I would just guess that it is less than class A amps (gain before feedback is few hundred) and much less than most class AB amps (gain in order of few thousands). It is also worth mentioning that conversion of voltage to duty cycle is done in one stage oscillator to drive output Mosfets while traditional amplifier requires multiple output stages (hence delays) to get signal from input to output. Negative feedback causes, as Atmasphere mentioned, late summing with input signal and overshoots (time domain) or enhanced odd harmonics (frequency domain). It is called Transient Intermodulation TIM and was unknown until 70's. Some class AB amps even have saturation of output transistors that causes momentary gaps (charge trapped at the junction)with fast changing input signals (our brain compensates but makes us feel tired) - not even possible with class D since output transistors are in saturation anyway (time is analog quantity and not the voltage). For the same reason class d amp cannot become unstable.

Icepower has multiple feedbacks. One feedback, I believe, is for output voltage while another might be controlling time.

* Class AB has additional problem of different (changing) trans-conductance (gain) crossing from one transistor conducting to both transistors conducting (around zero). It is voltage dependent gain that needs negative feedback.

Dob, as long someone is receiving financial gain beyond the customary hobbyist buying and selling, I think it appropriate that the potential for a conflict of interest exists. I welcome and applaud those in the business that provide a disclaimer for contributing here, and perhaps even take their opinion more seriously despite any possible perceived prejudice that might exist. On the other hand, I am very skeptical of those in the business that do not provide a disclaimer. It's very apparent that Henry is fairly new here, and deserves a pass.
I never said all Class D amplifiers use the same negative feedback, I don't believe that, and I'm not mistaken.
We used to have a regular contributor here (I'm sorry I don't remember his user name) that has been designing amplifiers (and provided a disclaimer) for many years. His latest company ((?)located in Texas) now specializes in Class D amps. It was he that suggested that when designing typical ss amps that he avoided negative feedback when and where ever possible, but that many if not most Class D amps have plenty of negative feedback, and it didn't seem to matter as much, perhaps due to the faster speed. Please accept my apologies for not being able to provide any verification.
Kijanki, has regularly provided excellent insight into amplification technologies and I don't doubt what he's suggesting for a moment.