Class "D" amp? I do not have a clue. Do you?

"With medium efficiency speakers the MEASURED peak voltage is above 100v."

- I don't understand it. What speaker efficiency has to do with the voltage. Icepower 1000ASP voltage is regulated always 80V and since it is bidirectional it becomes +/-80V.

Switching power supplies generate high frequency noise that is easy to filter out and non audible. For this reason Rowland uses switching supply in Capri preamp and he is very noise conscious guy (he used batteries in preamps).
Linear power supply is also switching - current comes in narrow spikes of very high amplitude producing high frequency noise in addition to 120Hz noise (difficult to filter out).

Now - In order to become 1/4 wave antenna for 100kHz SMPS frequency wire/cable has to be 2460ft. Below 1/10 of the wave (984ft) antenna practically doesn't work. Small amount of the amp's carrier frequency (1%) appears on the speaker wires but at 500kHz it needs 197ft of wire to become 1/10 wave antenna.

Kij has it correct. The RDon is very low for MOSFETs. Resistance Device on.
This is a big selling point for discrete power devices. less resistance is less power lost, or rather delivered to the load.....whichever you prefer.

Now, on to the full /half bridge argument.
http://www.irf.com/product-info/audio/classdtutorial.pdf

Above is the Internation Rectifier article on 'd' amps. Very good read. But, this is only part 1 of 2.
The full/half bridge configurations are well covered as are some of the rf issues.

QUESTION: how do the 2 different kilowatt Bel Canto amps differ? Don't they both use the B+O ASP module? Is there only a difference in input circuitry or the Zobel?

Here is a link to the B+O ASP site.
http://www.icepower.bang-olufsen.com/files/solutions/icepower500asp.pdf

Looking at the technical specs you will see the power output is specified for 60 seconds.....not FTC continuous. The ASP1000 module has only a 30 second time limit.

I like my 'd' amp. No question about it getting the job done.

Kij, How DID you know my speaker wires were 197 feet long? Just kidding!

As for the PS switching noise at the output, that is removed with the low pass Zobel. However, there are special filters used by the measurement crowd which test equipment. Some problems occur when measuring 'd' amps.

"Switching power supplies generate high frequency noise that is easy to filter out and non audible. For this reason Rowland uses switching supply in Capri preamp and he is very noise conscious guy (he used batteries in preamps). "

Hello Kijanki. By chance I owned Capri before I got my "heavenly" full tube Joule-Electra LA-300ME preamp. As strange as it may sound, this tube amp is more silent then Capri.

Next, I spoke with Simon from Spectron yesterday regarding asserion that high-frequency noise (or signal) is inaudible.
He says that then you emit hi-freq test signal it is indeed inaudible. However, then this hi-freq signal is a part of the mixture with other signals i.e. real music then due to the non-linearity it effects human perception of the music and effect listener fatigue.

He agreed with you, however, that future audio equipment will have only (perfected) switching power supplies even in class A ss amps - which will not have a weight of huge transformers and somewhat less of the heatsinks; the same with high power tube amplifiers.

fascinating topic !

Mike

"QUESTION: how do the 2 different kilowatt Bel Canto amps differ? Don't they both use the B+O ASP module? Is there only a difference in input circuitry or the Zobel?"

ref1000 is stock Icepower module in a nice box.

ref1000m has additional input buffer and power supply circuits. If you open up the box, the 3 separate circuit boards/modules are clearly visible. It is dead quiet and most nonfatiguing.

I have read that ref1000m effectively addresses RF noise concerns in comparison to ref1000.

I have never owned or heard any other Bel Canto amp so I cannot offer an assessment of sound differences. From what I read however, others sem to concur that there are differences.