There is no amplification in pasive electronics, that is why it is called passive. There is nothing but 2 variable resistors and a capacitor that shunts high frequencies to ground. The power you get is from the pickup, it is not amplified in any way. The signal is that strong to start out with.
In order to amplify a signal, you have to run it through an amplifier, a pre amp, is the amplifier before the amplifier. If your guitar doesn't have a battery in it, it does not have a preamp.