As far as the filter is concerned, the slope of the first-order pole is 6dB/ octave, and to reach 30dB/ octave, it is necessary to build a fifth-order filter circuit, including two-stage operational amplifiers.

In addition, it is obvious that your bandpass circuit works under dual power supply, and the output is AC signal, so it is unreasonable to directly trigger the 555 of single power supply;