The best way is to use a set of VCA (voltage controlled amplifier) chips which can be tied together and controlled from a single expression pedal resistor. Of course this would need a bit of electronics to be designed. Another option which isn't so daft as it sounds is to use LDR (light dependant resistors).. use the pedal to control a lamps brightness inside a closed box together with a few light dependant CdS resistors for altering the signal levels to each keyboard... You could also try replacing the potentiometer in thepedal with a 4 gang device...?

Simon

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