This is what I'm going to do:Are you isolating the (V+) & (V-) power supply pins for each of the four op-amp sockets?
If not, where are you breaking the +18V and -18V supply rails, and installing the Zener Diodes, to lower the op-amp supply voltages?
Edit: I changed the value to 2V2 because the V6 might perform better with a bit higher voltage.
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