for our Z series preamps, such as the TCLA tone control preamp and Aikido line preamp (no tone controls), these have been designed to be used with 100K volume controls and 250K balance controls.
I see that you are using a 250K volume control. This will work, but is not ideal. If possible, try and use the above mentioned potentiometer values.
If using those values, the loudness circuit component values are as follows.

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