perhaps in some designs, but you would have to be running the amp at 100% rms power levels for that to occur, (and the heatsinks would not cool appreciably) most speakers and ears would have been damaged. This argument holds no water. [/url]
Good reply - I do see your point now. I agree that at more modest levels the Class A is going to be thermally much more stable (run hotter but stay that way).
[quote] BTW what amp drives your ATCs?
These are active speakers so each speaker has three separate Class AB amps that run Class A to two-thirds power. The amp circuits are completely discrete (all individual components - no packages) and are actually very simple. They run rather hot when idle of course. The design uses a sliding bias so that the operation stays Class A until 2/3 power. The power output stages of the amp look like any typical simple amp design with two complementary sets of push pull high power MOSFETS - but remember each of the three separate amps are only driving one transducer (no complex crossover) over a very limited frequency range (so the work load is shared and kept as simple as possible - this is perhaps the biggest benefit of the overall design rather than the Class A operation). There is actually more complexity in the line level buffering/pre-filtering for each power amp stage which includes some phase adjustment to maintain accurate phase over the crossover. The three power amps to each driver are totally identical - so power output must be controlled/limited by the load resistance (woofer taking more power than a tweeter).