I think you should use linear VCA A-130 instead of linear mixer A-138 sending the original sequence to In 1 and  the output of the  S&H   to cv2 .   With gain at 5 and cv2 at 0 you should get a stable basic sequence of voltages (with lower voltages, being the amp ratio 0,5). Turning cv2 will add some randomness to sequence.

Mimmo