Buffer (Unity Gain Amplifier)

A good way for buffering one circuit to another to try and match impedances and avoid loading is to use an op amp wired as a voltage follower also known as a unity gain amplifier, which has a gain of 1, meaning what you put in, is what you get out. But has a very high input impedance, which then can take its input from a source and drive some other load, so it acts as a buffer between the two.                     Check under projects for  an RC time constant example circuit

unity gain amp
Unity Gain Amplifier, buffer voltage follower, with very high input impedance, so does not draw much current from the circuit going in to it.

Another way a voltage follower works is with a transistor wired in a configuration with the load connected through the emitter and to ground, this also follows the voltage at the base of the transistor, but with a larger current swing determined by the hfe or beta (gain) of the device selected, with a .7v loss from the original signal, (due to the base-emitter) so more or less it is the same voltage minus the .7v. If a darlington pair transistor was used, these are for current amplification, and are two transistors with their gains multiplied in the one package, this would cause a loss of 1.4v across the base emitter  junction compared to the input at the base.   This loss could be a problem if say for example, the load requires 12v and no less, and the power supply for the whole circuit is 12v,  then the load would only see 10.6v at a darlingtons output, due to the 1.4v loss, a 13v psu maybe required  or higher to cater for the circuit been designed. which can have a knock on effect in other areas which may require 12vdc, so voltage droppers or regulators may need to be implemented.