Plinius class A vs. class AB sound difference?

Whether or not you hear a difference between the two modes of operation on a given amp like the Plinius is going to depend on several factors. The first is how much power your speakers require to generate your average listening levels. This is directly related to impedance (because what we're really talking about is current and how much is required at a given frequency), and to a lesser extent sensitivity. The next factor is your room size, and then the third factor is how loud you typically listen.

In a small room, on efficient speakers, if you tend to listen in the high 80's or low 90's you may in fact never leave class A when in the sliding bias mode, hence you don't hear a difference between the two modes. However if you throw on a very dynamic piece of music, say Mahler, and play it full tilt boogie in a large room on inefficient speakers... well that's another story altogether. You will likely either be out of class A entirely or constantly at the bias point, switching between Class A and Class B (which is the worst possible scenario sonically speaking)

Now as for comparing two different amps from the same manufacturer, that's another story and it's hard to say whether a different amp will sound like the one amp in AB mode, or completely different.

OK I spoke to the manufacturer and they replied that SA amps work for 8 Ohms in class A upto the specified wattage: SA100 -- 100W/ch SA50 -- 50W/ch SA250 is certainly 250W/ch. For lower load impedance they switch to A/B operation type to double the current.
Plinius 8200p is not identical to SA100 since it has lower switching point to the class B and that point is relatively high as well i.e. ~25...30W/ch of class A. I assume that these two units have completely different power supplies and heat sinks if you just take a look even on the pictures of them.
Plinius 8200 MKII has M14 preamp and 8200p poweramp integrated into one chasis with separate power supplies for each part.
Overall I can say that there is a Plinius sound signature on all of above stated but flagship SA series are more open worm and defined.
Despite working in class A on 8 Ohm loads all of Plinius models love the heavy speakers such as Thiel, JM Lab or Apogee and to my thought they do the best job on them.

You owe it to yourself to listen to the Plinius SA 102.

I own an SA-250 MKIV and I can honestly say that there is a perceivable sound difference between AB and A (A sounds better, smoother).

I also tend to agree with HACKMASTER in that the amount of power required to drive the speakers will invariably affect whether or not you'll hear a difference between class AB and class A.

You’ll have to be able to stand the heat though. The Plinius amps run murderously hot in class A. You’ll see a difference in your power bill too. Happy listening!

My SA100 MKIII has just the slightest amount of grain in AB mode that is gone in A mode, also in class A there seems to be better definition, or maybe it is my imagination, it is that close. It sounds superb in both modes (driving Maggie 1.6s).