The thing I like about a crystal set is that it uses no power, so using an op amp is cheating a bit. 
also the signal is also sometimes very noisy, how can i reduce this? capacitor?
The way to reduce this is to make the LC circuit have a higher Q. This Q is a quality factor and is related to how sharply the frequency response is defined. That means it picks up less of the other signals and more of the wanted signal.
Some capacitors will give a higher Q tuned circuit than others. Here ceramic capacitors are not so good, mica and polystyrene are much better. But the thing that affects the Q the most is the inductor and the grade of ferrite. For an explanation see:- Inductor - Wikipedia