# Gain with inversing Op Amp on Equalizer

I know I posted a question about this circuit before, but I'm running into a problem. I know this is a terrible equalizer design but I'm trying to learn to put in use what I learnt with Op Amps and transfer functions.

I did the following equalizer using 3 band-pass filters with each one made of a high pass filter connected with a low pass filter via a unity gain op amp for low frequencies, mid frequencies and high frequencies.

I used a inversing amplifier with $$\V_{out}=\frac{R_2}{R_1}{\cdot}V_{in}\$$ for the gain and then solved for: $$\Gain=20\log_{10}{(|H(s|)}\$$.

The problem is about the gain I'm trying to get in each band pass filter. I tested it with -10 dB gain on the low frequency band pass filter, 0 dB gain on mid frequencies and 10 dB gain on high frequencies based on the resolution of the above equation with $$\R_1=1\$$ $$\k\Omega\$$.

The schematics is the following: And the simulation yields the following for the amplifier at the 3 different band pass filters: Where the only working gain is the 10 db on the low frequency band pass filter.

For example for the -10 dB gain: $$\20\log_{10}{(\frac{Z_2}{Z_1})}=-10\implies Z_2=Z_1{\cdot}10^{-10/20}\$$

So I don't know what's wrong.

Thank you very much!! 