Tone control using LPF,HPF,BPF

im working with the design given specifications required for us to have.
300 Hz (Low) -LPF
1 kHz (Mid) - BPF
4 kHz (High) - HPF

Cut Boost (Av dB) ±12 dB

Ive done my computations in LPF and HPF and i can show a graph using pspice that shows my computations are correct but INDIVIDUALLY. Meaning, i haven't used a summing amp yet to combine all of them. so here is a picture of the circuit of LPF and HPF (Individual)

ckthpflpf.jpg


lpfhpfsep.jpg


But if i connect both of them to a summing amp.
withsummingamp.jpg


graph looks like this:
withsummingampgraph.jpg


the gain should only be about 12dB. as far as i know Rf=Ri so the amp will become a buffer amp which is what i did in the summing amp. i dont know why it attenuated. help please.

what i want to happen is for example, if i have 3 inputs of different frequencies, low frequency signal will enter the LPF, the freq bet 300 and 4k will enter the BPF, and the freq above 4k will enter the high pass filter. a graph like this:

samplegraph.jpg


so what i did was to add a summing amp at the outputs of the 3 filters. Its like the purpose of the summing amp is to delay the signals so that they won't fight with each other.
 
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