The EVB3 emulates the (Key) Percussion facilities of the original B3. The Percussion facility is available only for the upper manual—as per the original B3. The effect adds the second or third harmonics to the attack envelope of a note. These harmonics quickly fade out, leaving the chosen drawbar tones.
The Percussion effect is polyphonic, but is only (re)triggered after all keys have been released. If you release all keys, new notes or chords will sound with percussion. If you play legato, or sustain other notes on the upper manual, no percussion is heard.
Note: Set the Perc parameter (found in the Organ section) to Only B, to simulate the B preset key restriction. If you want percussion to always be available, choose Always.