Negative Feedback a deal killer?

Magfan, to answer your question, in a power amplifier of conventional design (not class D IOW) the problem you face if you use local feedback as opposed to global is the issue of gain. IOW if the stage that the feedback is around does not have a lot of gain, it may not help you all that much. Where this really plays a role is in the output section, wherein if the amplifier is to conform to the ideals of the Voltage Paradigm (IOW, be a voltage source), there is rarely enough gain in the output section for said local feedback to do the job.

I did say rarely: the Ayre amplifier is able to be a voltage source without any feedback.

Anyway, you encounter many of the same problems with local feedback as you do with global, but overall I would say they are less pronounced, as (in theory) a single stage is going have a shorter propagation delay than an entire amplifier. This will tend to push the time domain issues to manifest at a higher frequency. That does have its good and bad side, so again a lot depends on the actual design!

How I see all this is very simple: as long as the amplifier fails to add **any** distortion to the 5th, 7th and 9th harmonics, then it all should be good. It will be even better if the lower ordered harmonic distortions fail to appear as well, although this is far less important.

Dob,

Mentioned Rowland 102, 201, 501 have standard SMPS without anything coming from Rowland. You can buy amplifiers with built in PFC like model 312 or buy additional power supply but most of Rowland Icepower amps have only standard B&O modules with integrated SMPS.

Please check power amp listed in my system before you make another silly personal remark involving elephants.

Magfan - local feedbacks are always better than global one but their application is limited.

Class AB amp design has to start with excellent linearity and wide bandwidth since one of conditions to eliminate TIM is to limit bandwidth at the input to one amp had before feedback was applied. Feedback can fix inherent class AB problems like "gm doubling" (different gains for small and large signals) but cannot fix poor design. AFAIK there is always some form of feedback (local one) even in zero feedback amp.

Atmo / Kij,
Processing your replys now........and they agree generally with what I had heard, which is why I brought it up.
Talking about feedback without qualification doesn't help a lot.

I also have felt that the B&O 'd' offerings have more in common than differences, no matter WHO packages the modules and what mods are performed.

One question though, about 'd'. For at least the ASP modules from B&O, they come WITH integrated SMPS. How do you get around that? Go to another module...the ASC(?) series which has no PS included?

Magfan - ASC series has also SMPS. I think that it was AP series but now Icepower makes different modules.

B&O SMPS are pretty good - very quiet (zero voltage / zero current switching) and very strong (1000ASP can deliver 40A output for 0.5s). What people often don't realize is that SMPS supplies are line and load regulated while linear supplies aren't. Linear supplies require a lot of capacitors to keep voltage steady and filter out 120Hz. They are also noisy since switching is done in audible frequency at max voltage. Linear supplies are also huge with big transformers. Small 1"-2" dia. toroidal transformer at 100kHz can deliver same power as huge toroidal transformer at 60Hz.

Best Icepower amps use 1000ASP with addition of extra supply that feeds over 400VDC. From what I read it has positive effect on the sound but module still uses its own supply. It is perhaps bunch of extra capacitors at high voltage (low losses).

Smaller Icepowers like 200ASC used in my Rowland 102 have higher carrier frequency and therefore wider bandwidth.

If you plan to use one, you might want to investigate input circuit that increases input impedance from 10k to 40k based on THAT1200 instrumentation amp (tiny board). That's the only Rowland contribution (other than beautiful case) to my amp.
I have to admit that he deserves credit for recognizing genius of Karsten Nielsen and B&O company. B&O was so fascinated with the project that they sponsored Nielsen's doctorate and gave him shares of company - first time in 70 years of B&O (being private company).