The drive PCB  just is a 1M pot.


The EQ is a follows:

---470p
|         
47k        Treble 250k
|
----22n
|          Bass 1M
----22n
           Mid 100KB (with 33K across)


Notes: The wiper of the treble pot goes to the MV through a 330k resistor.
The MV is 1M with 1M across