kevpat said:Well there is no such thing as a passive amplifier (as far as I am aware) as you need a power source to amplify. However I think you may be thinking about Passive pre-amps in audio applications. These are actually passive volume control circuits that take the place of traditional pre-amp circuits mainly because the signal output of cd's etc don't need an additional pre-amp stage so a passive volume control reduces cost and can improve sound quality (though this depends on how well you design the circuit).
Borber said:Passive pre-amp can be audio pre-amp consisting of connectors, switch and potentiometer. Audio power amplifier with enough gain (giving max power at nominal audio level) does not need any amplification in pre-amp, only attenuation (potentiometer).
Passive op-amp is nonsense.