Simple audio equalizer design: One filter is sending all the other signals to ground
The problem is that you are trying to use a virtual ground mixer on a single-ended supply circuit.



Figure 1.


The op-amp non-inverting input is biased to 6 V.
Therefore the output is biased to 6 V.
Moving the pot wiper will vary the voltage at (3) from 0 V DC to 6 V DC + the audio component.
Voltage at (4) will be rather messed up.


So you have two problems:


You can't connect the bottoms of the pots to ground when there's DC on them.
You can't feed ground-referenced signals into a single-supply virtual ground summing amplifier.




Figure 2. Adding decoupling capacitors at (1) and (2) will remove the DC from the potentiometers and allow the virtual ground (IC2D pin 13) to operate at +6 V.

Because you are using 1k potentiometers (on the low side) you'll need large capacitors at (1).