Voltage-Controlled Stereo Volume Control Using LM13600 OTA

What we can do with a stereo voltage-controlled volume control? There so many things, we can control our audio using a DAC which is controlled by a microcontroller, or we can use mono potentiometer with RC filter to minimize the scratched sound produced by a dirty potentiometer (I see this method in one of SONY audio products). Using a voltage-controlled volume control enables you to design your own tremolo effect, noise gate, dynamic compressor-expander effect and many more! The circuit’s schematic diagram is shown in the figure below:

This circuit uses excellent matching of the two LM13600 operational transconductance amplifier (OTA), providing 0.3dB channel-to-channel gain tracking (typical) volume control. Potentiometer RP is used to adjust the output offset voltage, and can be substituted by two 510R fixed resistors if you use the circuit in AC-coupled application. With the value shown in the diagram, the gain of the amplifier (Vo/Vin) = 940*IABC. [Circuit’s schematic diagram source: National Semiconductor Application Notes]