Originally Posted by Michael Bean
I was referring to what you said, "an all passive audio amplifier"...there is no such thing, for amplification to occur, you need an additional power source to amplify, there's no free lunch.
You are assuming _power_ amplification is the only sort we talk about - it isn't. A transformer can serve as an MC preamp section, giving voltage amplification completely passively. Mechanical amplification can be done passively with levers gears etc, so long as its position or velocity of force amplification rather than power amplification.
Amplification is about making some physical quantity bigger, and not all physical quantities are conserved like energy/power. In electronics we talk about voltage amplification, current amplification and power amplification - most commonly active, but sometimes passively. Power amplification of course requires active components, but the other sorts are sometimes passively boosted with transformers or switched capacitors, etc.
[ actually switched capacitor networks are interesting in that the power is not supplied/amplified by the switching device, but rather only routed by them, hard to say if this is best thought of as active or passive ]