What is wrong with negative feedback?

Jamesgarvin I had a pair of Manley ref 440/200 monos that had adjustable slopes and feedback to custom taylor the sound;there were noticable differences but I did not consider it annoying just different.

Unsound - Feedback in Icepower amps is called Multivariable because it consists of two feedbacks controling voltage and time.

I suspect that feedback in class D is less evil for few reasons:

Amp cannot become unstable (oscillate) since it is already oscillating.

Response can be very fast limited only by Mosfet's max current and resistance (sort of Hysteretic converter)

Voltage feedback is shallow because duty cycle is more linear than transistor characteristic(less feedback required) and also because "time feedback" already corrected most of nonlinearities. I suspect that voltage feedback is helping to deal with load regulation. Early class D amps (Tact) had no voltage feedback at all and were sensitive to load conditions.

Momentary saturation of output stage (charge trapped at the junction) that happens in bad cases of class AB is irrelevant since time (duty cycle) and not the voltage is analog quantity.

When I first heard the IcePower amps in my setup, the difference in the nature of teh sound from anything I had heard prior was most startling. It was most apparent in that major volume adjustments seemed to have comparably little effect on volume, though the SPLs were clearly increasing as expected.

My observation of how the IcePower amp sounds as volume is increased seems consistent to me with what Ralph describes as the benefit of not using feedback and loudness cues. Most really good systems I have heard over the years tend to behave this way more or less I believe.

At the same time, Icepower applies negative fedback clearly. So I have to conclude that the IcePower amp has achieved a lot of teh benefits that Ralph attributes to no feedback in its specific implementation.

If so, another reason why Icepower/Class D can be considered a major innovation in home audio along with the other advantages.

Kijanki, I could be wrong about this, and perhaps it doesn't matter, but, I don't think Ar_t 's amps were ice amps.
Have the TacT amps changed since then?

Acoustat6, yes, sometimes I do. Most music does not demand it but some does: The Verdi Requiem, on the Soria box set (RCA) is a good example of vinyl being put the limits, and stereos too. If you play the quiet spots at the correct volume, the peaks will be at 115db.

So- to answer another question- 115 db peaks occur front row center, equivalent to where the microphones are usually placed. When you are in the orchestra, you don't get the same volume exposure that the audience does unless you are in the percussion section.

Some of the class D amps do not have feedback as well as some transistor amps as I have mentioned. Some of the class D processes allow for time manipulation, which is a fancy way of saying that they have a way around this issue. I don't doubt that this may be part of why class D amps are challenging the traditional transistor art.

However the artifacts I am talking about also occur at much lower levels. BTW, it is odd ordered harmonics that allow SETs to have the 'amazing dynamics' that are so often associated with them despite their low power levels. When an SET is at low power, it makes no odd orders at all, but when you push it over about 50% of full power or so, they begin to show up. Since it is the transients that take all the power, that is where the loudness cues are now occurring too. As a result, an SET with low power might seem to play so loud that 85 or 90db seems like a lot. This is the effect of artificial enhancement of the natural loudness cues.

As a result I am careful about using the word 'dynamics' because so often when I hear audiophiles use the term they are really talking about 'distortion'.

If you can't be in the room with musical peaks at 100 db (if its uncomfortable or sounds too loud), then its very likely that the odd orders are being enhanced.