additive synthesis

hi guys, wondering how i can do this, without continued addition after i have let go, trying to work my way through learning max have started with a simple sawtooth synth comprising of 16 sine waves, i also managed to get them to add and play using the computer keypad, however i can only get it to continue to add after releasing the notes, even if i only hold down the button to play say a G, the waves for C, D etc. will still set off greating a very nasty clash, any ideas how to solve this?