I am trying to design a bandpass filter that would have cutoff frequencies at 150Hz and 500Hz. The main purpose of this will be filtering notes played on a piano (or generated pure tones) that are outside this range.
I have been trying a lot of architectures on Multisim but unfortunately all of them seem to be giving frequency responses in highly negative dB ranges (-100s), and some don't even behave in the way I expect them to.
I also noticed that changing the op-amps in my designs changed the behavior of my filters quite drastically. For example using LM741 and LMC6464 caused very different frequency responses. Also, in some cases connecting the negative rail to negative voltage made a significant difference compared to connecting it to ground. Unfortunately, since I don't have a way to get negative voltage (or at least not one that I'm aware of) I have to use ground.
I would appreciate any tips on building this filter and also any insight you can share into why I get this sort of behavior (negative dB freq response, completely different response with different op-amps). Even though I'm mainly interested in building an active filter, I'm open to any suggestions and designs in building this filter. Thank you very much for your time and help.