Pass Labs x350.5 & Classe ca-m400 class a power?

Tpsonic: I agree about the sonics... get the Pass 350.5

or get the 250.5 and get a X1 preamp... Remember the preamp is just as if not more important than the amp in transparency.

Single ended means that a single active device(or paralleled set of active devices) handles the signal. The active device could be either a tube or a transistor.

The alternative to single ended operation is push-pull, where one active device (or paralleled set of active devices) handles the positive parts of the waveform and another handles the negative parts of the waveform.

For audio use, a single ended stage must run class A. A push-pull stage can run class A or class AB, depending on biasing. In pure class A operation, neither device in the push pull pair ever shuts off.

In class AB operation neither device in the push pull pair shuts off on small signals but on larger signals one device is off while the other is processing its half of the waveform. Effectively the amp runs class A for small signals and transistions towards class B as signal strength increases.

The higher the bias (and the hotter the amp runs) the longer the amp stays in class A before moving into class AB as the signal increases.

Pure Class A amps are inefficient and draw twice their rated power from AC line constantly. The power draw is independent of the amp's output and most comes back as heat. They are space heaters.

As I type this I'm listening to a pair of Pass Aleph 1.2 single ended mosfet monoblocks. Each is pulling about 500 watts from the AC line and the room temperature has risen 8 degrees in the last 2 hours. But they sound divine!

I vote for Pass also.

Thanks everyone. Honestly, I am undecided between the Classe and Pass. Those of you who recommend the Pass, can you please let me know why you think it is better than the Classe? Who has been able to directly compare Pass and Classe?

By the way, I am considering the X1 + x350.5 or the CP-700 + CA-M400. Any thoughts in these pairings?

Tboooe, of the pairs you've suggested I can only say that I own the X1, and have heard the x350.5 (but that was not in my system). The X1 is an awesomely quiet, very neutral preamp. Nicely extended in both directions, with a very nice midrange. It is one of the best preamps I've ever heard. There is another thread where it was remarked that - in comparison to a great tube preamp - the X1 mids are thin and bare. Frankly I can't agree. I'm not sure how much system dependency the X1 has in placement with other components, but in my system (driving a Van Alstine FetValve amp) I get a satisfactory midrange indeed. Tonal colorations, a real organic presence.

My recollection of the x350.5 is that it is also a fine sounding piece of gear. It was being driven by the X2.5 and I thought the pairing sounded very musical. Maybe just on the shady side of neutral. I can't remember what source was being used, though.

My only complaint with the X1 is that the gradation between the volume click stop positions is too large (about 1.25 dB).