lazcook

Im an industrial designer, and have started to learn about electronics and have building a simple bat detector circuit. The circuit is shown below but there is not enough gain from the signal to light up the led. All I want the circuit to do is light up an led when there is a signal at 40khz. I need to use a series of inverting amplifiers to boost the signal. Could anyone show me how to integrate the amplifiers in the circuit below so that the led will light up with it detects a ultra sonic sound. In research I have found that a boost of around 4,000 times the original signal is needed. My circuit What I need to put into it [img width=680 height=567] Thanks for your help any suggestions or designs for how I put in these op amps would be appreciated.