[chuck-users] fm?

hi list i try to play around the fm unit generator and i can't make it work although i can use class depending on the FM class (TubeBell for example). this simple code make my jack server break out : FM f => dac; 400.0 => f.freq; while(true){ 1.0 => f.noteOn; 10::ms => now; } does anyone had already met some trouble with this class?