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

Pugstub - It might be related to fact that Icepower's full bridge places half of supply voltage (30-40V) on both speaker terminals. Non-powered speaker sees only voltage between terminals (difference) but ground referenced powered speaker might not tolerate such common mode voltage. They also mentioned in Stereophile that some electrostats don't work with Icepower for the same reason. Half bridge schemes like Hypex don't have this problem and can be even bridged while Icepower cannot be (already is).

Spectron: DC offset can harm your tweeter, depending on the tweeter design and degree of DC Offset

Simon, can you clarify why that would be? I would expect any reasonable amount of dc offset to be blocked from reaching the tweeter by the capacitor(s) in the speaker's crossover network. Aside perhaps from transients during turn-on and turn-off, or during times when the amount of dc offset might be changing, and in each of those cases I would expect the resulting transients to be minor and brief.

Thanks!
-- Al

Another possible contender, that is not like the

"typical" Class D Design; But is able to sit in, with

the Best of the Class A, AB, Designs ANY day. IMHO.

I have the PS Audio "Gain Cell" amplifiers, they are a
"Hybrid" Class D Design.

The GCA-500 is the 500wpc@8ohm and 1000wpc@4ohms

The GCA-250 is 250 wpc.@8ohms and 500wpc.@4ohms

Bass is "Natural", in other words, it is exactly

as the Recording captured it.

Not too deep, or "over-damped", but just right.

The mids. are as smooth as I have heard, with the highs,

not EVER "searing" I own Horn speakers, that are very

sensitive, so low level listening, is mostly how I listen.

These amplifiers, have the uncanny ability to deliver

that very 1st watt, with Authority!

We All, have our favorites, and what is "great" for one,

might be down right, "nasty" to another.

All I can say is that I enjoy Music at a Level I NEVER

thought possible.

Given a set-up that is really "tight", IMHO if you add

either one of the above amplifiers, whether, it it Music,

or Video, the PS Audio, delivers the goods.

*****Bass
*****Imaging
*****Soundstage
*****Pure Enjoyment
*****Forget the Electronics
*****Value
*****Ability to reach 120db.
*****Lack of Heat

From the PS Audio site...
The GCA 250 is a two channel, 250 watt per channel power amplifier that produces 500 watt per channel into 4 Ohms and drives down to <1.5 Ohms. It has a damping factor that exceeds 1000 and is the amplifier most people will want to own as its 500 watt per channel rating is more than enough for any loudspeaker system we know of, period. The GCA 250 has an input impedance of 47K Ohms, can be remotely turned on/off with a simple 12 volt trigger, is a fully balanced amplifier, and like the GCA 100, it’s ear in the tweeter to hear any hiss out of this amplifier. Distortion levels below 0.1%. The GCA 250 is the amp of choice for any system whether it’s a stereo or multi-channel application. This beauty can power anything.

The GCA 500 is a brute. This is one of the most powerful amplifiers available at any price from any manufacturer in the world. The GCA 500 is a no holds barred stereo, 500 watt per channel power amplifier that produces an incredible 1000 watt per channel, both channels driven into 4 Ohms and is drives down to <1.5 Ohms! It has a damping factor that exceeds 1000 and is the amplifier you will want to choose if you never want to worry about headroom or dynamic capabilities in your system ever again. The GCA 500 has an input impedance of 47K Ohms, can be remotely turned on/off with a simple 12 volt trigger, is a fully balanced amplifier, and like the GCA 100, it’s ear in the tweeter to hear any hiss out of this amplifier. Distortion levels below 0.1%.

The GCA 500 is unequalled in the world of audio amplification. The king, the biggest, baddest power amp around that can play the sweetest violin passage to the loudest rock and roll, dinosaur stomping audio experience this side of the galaxy. If you’ve never witnessed true audio power with limitless headroom and breath sucking performance, this is the one.

They do benefit from a good power cord.

Balanced Interconnects of the Best quality.

I Love Music!

"Ref1000 can drive 2ohm delivering 40A "
That means that its peak voltage is 40x2 = 80 volts. Its not bery good!
With medium efficiency speakers the MEASURED peak voltage is above 100v. This why Spectron amps have peak voltage of 240 volts (to cover poor efficiency speakers too). As I understand switching power supplies also generate high frequency noise. I believe these are two the main reasons why high caliber class D amplifiers like Spectron and Mark levinson (No 53) use traditional transformers.
The single exception is Jeff Rowland 312 which uses switching power supplies with PFC (power factor correction) and for its $15k price provide very good sound.

DC Offset: any semi-decent amplifier ( e.g. Spectron I own and enjoy!) has protection circuitry. Richard Vandersteen may have some bad experience with either old design or new "cheap" class D amp. Today its not a problem (if done right)

Mike

"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.