Op amps boosting Ultra sonic signals?

[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.

[audioguru]

Hi Laz, Welcome to our forum. ;D
The old LM358 opamp has poor high frequency response. It can't reach max output above only 5kHz and its max gain at 40kHz is only about 10.
There are many newer opamps with a much wider bandwidth but my favourite is the TL071 single, TL072 dual and TL074 quad low-noise wideband opamps. They have max output higher than 100kHz and their max gain at 40kHz is 45.

Three opamps can have a gain of 16 and connected in series for a gain at 40kHz of a little more than 4000.