Pass Labs xa - .5 amps

I don't believe the XA-.5 series are single ended Class A. There are very few single ended Class a solid state amps. I believe the First Watt is one.

Here's a white paper about Single Ended Class A written by Nelson Pass, the designer of the First Watt.

I think if the A-30.5 needle is moving around that you might be exceeding it's power limits. Not sure, though. You should contact your dealer for further info.

Seems to me that Audiofeil might be in the position to offer the best advise on this one.

Unlike most amplifiers the meter staff on the XA.5 series indicates bias, not power.

It will move only when the amplifier exceeds its' rated output.

Dealer disclaimer.

I would imagine it would tend to exceed its rated power on peaks, which can happen often. Is it necessarily a bad thing that the meter moves, or is that to be expected with music dynamics and nothing to worry about if everything sound fine?

So long as the amp output is not exceeding the bias point (in Class A operation) the staff does not move.

Above bias point, the XA.5 amps will source something above rated wattage (they have about 4 dB headroom) and at that point the staff will swing right.

At that point the amp is still in Class A to the rated wattage, but above rated wattage it's A/B. This would be the classic A-A/B operation.