>Class A uses tubes... Class A amplifiers can be made in solid state as well, very easily. As a truly simple, DIY example: http://headwize.com/?page_id=31 http

>Class A uses tubes... Class A amplifiers can be made in solid state as well, very easily. As a truly simple, DIY example: http://headwize.com/?page_id=31 http://headwize.com/?page_id=31 There's nothing about solid state that requires a circuit that "outputs a bunch of pulses, and then applies a low-pass filter" -- true linear amplification exists in the transistor domain just as well. And even if solid state did require quantization (beyond the shot noise that vacuum tubes suffer from also), given that we can do direct digital synthesis up to the 100's of MHz regime pretty easily these days (i.e. beyond the bandwidth of most audio tube amplifiers), with 24+ bits of resolution, there's no reason that a solid DSP system couldn't emulate a vacuum tube response well enough to be electrically indistinguishable from the actual tube. But, as the grandparent post notes, it's one heck of a lot easier/cheaper to just use vacuum tubes. Which is why I'm staring at a tube-based headphone amplifier on my desk right now. Though it does use solid state buffers, which incidentally are way more linear than the typical ways -- capacitors, transformers, etc. -- of removing the DC offset inherent to tubes...