I've got an LM13700 in this VCA configuration, and for whatever reason the gain control input (I'm applying a triangle LFO, ranging from 2-7v) is appearing as a voltage at the output. Does anybody know why this could be happening? :
With change the bias current (gain) of the amplifier, also changes the input bias current and the input offset current. The input offset current generates voltage at 470 Ohm resistors, which is more visible at the output of the amplifier.
It will not be perfect, but it can be improved:
-With smaller resistors at the input (470 Ohm > 47 Ohm).
-By zeroing the initial offset voltage. (Minimum triangle signal at the output without input signal.)