Negative Feedback a deal killer?

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).

I've lost track of what B&O makes. Here is link to ASP module....I suspect as used in my PSAudio GCC series integrated::

The data sheet lists 50v and 80v outputs...with which to feed the extra, non power supply equipped modules. The 80v is listed as 7 amps, If I remember correctly. These numbers are with the 'home' amp having zero output....

http://www.icepower.bang-olufsen.com/files/solutions/icepower500aspdata.pdf

The GCC series is a so-called variable gain design. The input circuitry is handled thru something called a 'gain cell' which I HOPE takes care of any impedance mis-match with any source connected.
The balanced inputs from my CD player are wonderful....

Thanks for the responses. My speakers are Coincident peII's w/ a flat 8ohms load and 92 db. Aljordan's comment about znfb used with easy to drive speakers is true, I believe at least in my experience. The Unison would be used on the same speakers. I try to stay away from "hard to drive" speakers as it limits your amp choices too much. I prefer SET amps, or tubes in general. Atmasphere hopefully someday I can listen to one of your amps, no dealers in my area.
Thanks
Mike

"...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. "

Kijanki, I am not EE so I cannot argue professionally. However, everybody knows that with exception of Jeff Rowland only class D amplifiers use SMPS supplies and the rest of the world use "huge" linear PS. So, there is something "there" in SMPS not so positive... Again, I just am making an observation.

Dob, I disagree with you. Jeff Rowland uses his SMPS with PFC (for Kijanki - on his premiere amplifiers) but he is not the first. See below from Spectron web site:

" Spectron designs team won a contact with pro audio giant Inter-M (among others in competition were Bang & Olafson and Philips) to build a highly reliable continuous output 8000 watt power compact digital amplifier. We successfully demonstrated a prototype of the first stage of this unique amplifier at the NSCA (National Sound Contructor Association) meeting in Orlando Fl , in March of 2007. The highly innovative design includes very high level power factor corrected switching power supplies using the latest PFC conversion technology and resonant mode DC:DC converters"

I can't even imagine amplifier with continuous output (rms) of 8000 watts and who needs it (besides its use in Madonna concerts :-) but they also use SMPS supplies with PFC and DC:DC convertor at least since 2007

I spoke with Simon Thacher from Spectron about the fact that they use in their Musician III amplifier linear PS and not their SMPS, a while ago but I can't remember a word of his reply, today. So, I can make two points:

1 - If to use SMPS then only with PFC + DC:DC Convertor
2 - Even SMPS w/PFC are not automatically better then linear PS - as Spectron has both types and uses both on two different amplifiers.

Finally, I agree with Magfan and Dob that ".. 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 ". I think, one need to hear Kharma, Weiss, Spectron etc to see true potential of class D technology.