The best subbasses I get is using the synth filter itself if it has some sort of tracking option (ie, control the filter with the keyboard). Set the ressonance to the max (self-oscilation, gives you a pure sine wave) and control the notes with keyboard. Filter envelope will work as a pitch envelope (nice for the Juno). Just make sure you don´t blow your speakers with the high ressonant sound. You usually have to reduce the output level, but this way you can get really deep smooth subs.