The original TB-303 had a kill switch hooked up to the LA 4140 (Headphone Amplifier), which makes sense, because the LA44140 is the only draw of the +6Volt power.
This is entirely theoretical, but you might be able to change the circuit so that the LA 4140 can be used as a Distortion, and/or EQ circuit.
You'll need the Datasheet If you are going to get far with it.
CategoryMods