Hey thanks for the replies Andrew! What you said makes perfect sense.

I'm really excited to own a 3 channel ADA-1500 now even more! As suggested before, I think I'll just run the rears off my sc-61.

sigh...it feels like it's going to be forever by the time I have a complete stereo. lol

I've been building it bit by bit. I still need a subwoofer. Still need a pair of QS8's. Still need a power amp.

I'm getting there though

I literally JUST received a vp160...god what a dominant center. I love it. It makes people's jaws drop when they come in my house. lol

Brilliant posts, Andrew. Thank you.

I'm still thinking on how to drive all my speakers.... One question on the Axiom Amp is why the toroidal PS over Switch Mode PS?
Thanks
Nathan

From Axioms products page;

"By combining a class-D amplifier with a toroidal transformer and a large storage capacitance, you have the muscle you need to deliver power where it's needed, when it's needed."
and
Realiability

Sorry if this has been said.. it's a long thread!

Those linear power supplies (which prefer to draw their line current in big horrible spikes, and would love a chance to intermodulate your music with rectified line voltage), combined with the inherent nonlinearities in both class AB and D output stages, tend to complicate amplifier design a bit more than Andrew is letting on.

Using huge capacitor banks, minimizing dead time (in class D), raising bias current (in AB), shielding, etc. all reduce the distortion and noise somewhat, but what really makes the difference is the control loop.

What makes the Axiom amps better than the previous generation of class D (and what I'm surprised I haven't heard people talking about) is the way they generate their switching signals; they are essentially self-oscillating delta sigma modulators (similar to a lot of ADCs / DACs). The control loop in this type of amp acts as a low-pass filter for any signal that shows up at the input, but a high-pass filter for the noise that's generated inside the amp. This essentially separates the "good" and "bad" signals into different frequency ranges, with the "bad" being moved up where you can't hear it, and then directed right into the stop-band of the output filter. It also lends itself to tight control with high loop gain over the whole audio spectrum, and allows the control loop to accurately account for the time the output stage spends in between the rails.

I could see it being sensitive to higher frequency EMI though.. hence the linear supply?

This might sound like a trite answer but it's not intended that way... since AFAIK typical power amplifier power supplies are not regulated there's no inefficient linear regulator to replace, so the main application of switch-mode power supplies in power amps would be dynamically adjusting the rail voltage of a linear amplifier to reduce the amount of power being dissipated in the output transistors on average.

Since the Axiom amps are basically "switch-mode amplifiers" they can use a simple (but big-ass) power supply without burning energy up as heat anywhere.