Dave Smith Instruments SYNTHESIZERS

ok, lets say I want to only use 1 voice for drone type sounds.  I turn 
it to mono mode and then as I raise the Amp level to get my drone 
sound, ALL 4 of the voices are sounding.  

I am not striking any keys, just raising the AMP level.  Is there a 
way to shut the other 3 voices up and only hear 1 voice?

Thanks