Class A, AB

Here's my question about the Plinius, and others, but I'll use the Plinius SA100 for example.

Rated at 100W stereo into 8 ohms. More into 4 ohms and all the way up to something like 650W into 4 ohms as a bridged monoblock. It would be silly to think all of that would be class A. How much, I not really concerned about but it does indicate that the load plays a role. It still draws the same 500W from the wall, in class A bias, which was about 40% efficiency for that 2 X 100 watts. I haven't bothered to put an ammeter in there to see if the draw jumps up when I get it loud. That would have to be VERY, VERY loud.

The origional Pass XA series (unique feedback/stabilization) and most tube amps are different. They don't vary output to the load, as much.

Aldavis:
I am the opposite orientation on the A vs. AB choice -- after some intial experimentation and excitement about the sonic benefits of the class A mode, now I almost never go that route -- not so much concerned about the electrical use as the heat factor -- that is troublesome in a way that is not so easily overcome. Also I will say that in the case of Plinius at least, they are phenomenally close in AB, so I guess that makes me a "non-critical" listener for the most part.

Ngjockey:
According to the SA100 manual (page 6) "The current from the mains/line supply by the amplifier in BIAS A is now approximately 1,000 watts." So looks like the current draw actually is up by quite some margin to use it this way, also should be constant (see below).

Elizabeth:
Page 21 same manual:
"A class A circuit topology is one in which the total current the amplifier is capable of delivering, is kept flowing in the circuit regardless of the demand....
In a Class A circuit, current draw should be constant therefore there is an absence of the power supply modulation common in Class AB design amplifiers."

This under the heading of WHY IS CLASS A BETTER? So again, it sounds to me like these amps are switchable from Class A to AB.

>>Also I will say that in the case of Plinius at least, they are phenomenally close in AB<<

That depends to a large extent on the speaker as well.

It's very difficult to evaluate an amplifier based on one speaker.

Your Plinius may sound terrific on speaker A and like a dog on speaker B.

My analogy is also applicable to tonearms and cartridges.

Oh yes, there is little doubt that when it comes to audio review, people are not hearing the same thing. That is why the only real way to determine if a given component is for you, is to buy and listen in your own environment -- enter Audiogon.

Interestingly, I try to stay away from really narrowing down what something sounds like because of this factor, and whenever I break from that, inevitably it has a predictable result. Had a buyer recently work really diligently trying to get me to characterize the sound of a piece I was selling. I explained my position, but gave at least that it was one of the more "dynamic" pieces I had heard. He bought it, and was happy, but one of his first comments: "Does not strike me as particularly dynamic." All I could say is "there you go..."