Negative Feedback a deal killer?

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.

Michael_moskowich,

Rowland uses SMPS in all class D models (including integrated). In higher models like 312 or integrated Continuum he uses additional PFC unit. For the rest like 102,201,501 you can buy external PFC unit. Such unit supplies about 450VDC and you don't need any DC/DC converter (term tossed often to impress people) because B&O module can be supplied directly with 450VDC.

There is more than 100 companies manufacturing class D amps any many of the use SMPS. Example of company that uses only SMPS is Bel Canto, NuForce, Red Dragon.

New Rowland high end class AB amps costing $48k also use SMPS. Read this thread:

http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1263307524&read&keyw&zzcriterion

For class D amplifier SMPS is obvious. If you think that class D amp is good enough then SMPS, that is the same thing (class D), should be as well.

I know, you know all that and am just restating but as for the rest of the world using only linear power supply - I don't know. I wouldn't risk such statements without checking. Others with more experience can perhaps help but I remember that Linn amplifiers have SMPS and are not a class D amps. Even some preamps like Rowland Capri use SMPS. I can tell you that linear power supply is easy to design in comparison to SMPS. In addition there is natural resistance as it was at the beginning to class D amps. It is very difficult to change opinion of people (like you) so designers design for current demand (I don't blame them).

One more thing - PFC is not conversion but correction. It is beneficial for power company but not so much for the end user (lower overall efficiency since PFC unit has its own efficiency <1). What counts is just whole bunch of electrolytic caps at high voltage fortifying SMPS but the same thing (extra capacitors) could be included in SMPS to start with. Again "PFC correction" is more impressive than just "extra caps". Bel Canto has similar thing inside of cabinet but they call it "increased energy storage". Their amp Ref1000M made Stereophile class A rating. There is not so much sound difference from the original Ref1000 but it allows some critics who made previously stupid reviews to save face and reevaluate (Martin Colloms gave this amp score of less than one of 10).