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I have a Kent Armstrong MM3 bass preamp and i only have 4 holes on my bass. I want to wire it with a stacked 250k vol/vol pot then bass, middle, treble. Can anyone help me on how to wire this correctly up i have found diagrams online but its confusing. any rough diagrams would really help me out.

according to the diagram image you posted, you can convert the blend into a stacked V/V pot .... but you will still have a master volume knob (R4)

I would contact the manufacturer directly with your question.

Depending on the pot value, it may be easier to convert the Bass/Treble tone controls into a stacked pot to conform to your 4-hole configuration

Master Vol + Blend + Mid + Bass/Treble