Pass Labs xa - .5 amps

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.

Then, what's the class A/B rated wattage output above class A operation for the XA30.5?

I thought this amplifier was only class A.

Despite the marketing hype, I believe it's not at all uncommon for some supposedly "pure class A" amps to drop into class AB at some point. Perhaps due to volume demands, perhaps due to impedance load, perhaps it can't draw enough power from the wall, perhaps it can't dissipate the heat and perhaps because the manufacturer is exagerating it's products capabilites. I think I would prefer an amp to slide into class AB rather than choke on class A and run out of steam or worse yet damage my speakers. This might partialy explain why some might choose a high powered Class A A/B amp with their particular speakers.

AFAIK there is no reason to think that any competently designed class a amp sliding into ab will damage speakers. The amount of class a delivered depends upon the bias current. Read Nelson Pass's paper on the subject on his web site. For high output solid state amps the inherent inefficiency of the design, however, requires huge power supplies, lots of heat production and large heavy heat sinks. Any manufacturer of a high output solid state " pure class a " amp which does not exhibit these characteristics is indeed exaggerating its capabilities. Reasons to choose ab over pure a include the desire for a small cool energy efficient amp or the need for very high output ( >500 watts) which is not very practical to achieve using class a. - Jim

Aldavis, I'm not sure if your responding to my post or not. If so, I don't believe that I suggested that a Class A amp sliding into class AB would damage speakers. What I was suggesting is that over driving an amp could damage speakers.