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

Afc - Ref1000 can drive 2ohm delivering 40A. Size of power supply has nothing to do with it since 2" toroidal transformer at 100kHz can pass as much power as 10" toroidal transformer at 60Hz. In addition voltage doesn't drop since it is line and load regulated. Traditional "linear supply" needs a lot of caps because of voltage drop and necessity to filter out 120Hz (difficult to filter out and audible) vs. SMPS high switching frequency (non-audible and easy to filter out). A lot of caps in parallel have a lot of inductance - not desirable since it is in series with the speaker. SMPS is in reality class D amp (origin of class D) and got bad rap only because of cheap computer power supply implementations.

"A Class D amplifier has one output stage fully "off" for half the cycle"

High efficiency of class D is not caused by switches being OFF. Speaker is always connected by Mosfet switches (there is no OFF) but direction of current changes. Icepower uses single supply and full Mosfet bridge reversing output while Hypex uses half bridge connecting output to positive and negative supply. Efficiency comes from the fact that Mosfets in ON state have very low resistance (in order of 20mohm).

Replacing in class D analog voltage with analog time (duty cycle) allows to get rid of nasty problem of output transistor nonlinearity that in class AB is corrected by deep negative feedback that causes transient intermodulation (TIM) and exaggeration of odd harmonics (unpleasant bright sound).

I don't understand mentioned output voltage offset of class D amps. It has as much offset voltage as any other class amp without output capacitor (it uses feedback/servo to zero output). Self zeroing is probably responsible in my Rowland for 5Hz (and not DC) bottom frequency range.

According to R. Vandersteen, DC offset is only a problem in their speakers with a powered woofer (the 5,7, and quattro). Using the class d amps in their other speakers does not cause any concerns. I just spoke with him this afternoon about this.

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!