I think Seth is on something here , It still boils down to the power supply for the headroom . So in most cases ( except the Flagship recievers , like said above by Soundman ) , The Mid priced power amps with a good power supply design will win out in Headroom and will not blow your tweets .
I'm getting involved again in this thread with a little reluctance, as I think it is a slightly destructive thread. However there is a little misunderstanding.
The issue is the biasing of the output devices.
Now the issue is Class A versus class A/B biasing.
Now the biasing determines the current through the output device, quiescent and operating.
Now in class A biasing the power through the output devices is constant, irrespective of load in the operating range of the devices. So there will be the same power consumption whether the amp is doing nothing or delivering its rated power.
Now what is the point. Well it has to do with the symmetry of the two halves of a sine wave. As you move to class B biasing the two halves of the sine wave become just a hair out of sink at zero point (the crossover node). This is called crossover distortion and has a lot of unpleasant third order content.
Now as you move to class B the amp runs cooler and more of the power goes to the load. A pure class B amp does not sound pleasant.
The vast majority of transistor amps are variations of Toby and Dinsdale's A/B configuration of the sixties. The object is to have the amp biased at class A on low level signals and move towards class B on the higher level signals.
Now obviously the more an amp is biased to class B the more efficient it will be and the cooler it will run and generally the output devices have a longer life. In the specification of power transistors there is a time heat longevity curve. The penalty is increased odd harmonic distortion. The question then becomes, how much is audible. This is the crux of the tube versus solid state debate. Tube amps are biased class A.
Now if you are packing seven amps in one case, you can't generate a bunch of heat, also if you bias too far to class A in addition to heat you will likely embarrass the power supply. As it is, few receives can have all their amps develop full power at once.
Now the other interesting classes of amps are class C and D. The class C was the invention of Peter Walker, and is a Quad patent, now held by IAC. As far as I know the Quad 909 is the only amp available currently that uses this interesting topology. The 405s especially the 405 IIs are snapped up for a good price on eBay every time one appears.
Now the class D is the switching amp where the input signal modulates N channel MOSFETs. Since these devices are acting as low resistance switches the heat generated in the devices are minimal. Until recently these amps have only been suitable for subwoofer use. However new approaches using Pulse width modulation of the input, are putting excellent class D amps on the market. Hopefully this will relegate the above discussion to history. As I have stated previously this should allow the amps to reside in the speakers. When combined with new digital crossovers this will be the preferred location.
