We need Audio mixer circuit For to Amplify multiple and different Audio inputs with a single Amplifer. Here simple and easy to construct Audio mixer circuit designed by using IC LM3900, it is a Quadruple norton Operational Amplifier comes with 14 pin Dual inline package.
The LM3900 operates with wide range of supply voltages (4.5V to 32V) and has internal frequency compensation, By using this circuit we can mix and amplify four different audio inputs and indivitual Audio input gain can be varied by Variable resistor VR1 – VR4. This circuit will give only mixed audio output signal with minimum gain and you can use external amplifier to strengthen the Audio output signal.
4 Channel Audio mixer Circuit diagram
Construction and working
To make audio mixer circuit we need amplifier stage and here LM3900 IC is used as amplifier stage. All internal amplifiers are employed to amplify the audio input signals, Each Audio input is controlled by Variable Resistors (VR1 to VR4) and hence we can easily control individual audio channels. Inverting input of Amplifier gets the audio signals and non inverting pins are grounded, for feedback setup 1M Resistor is used for all stage. Finally the output singnals are combined for external power amplifier.
It has 14 pins for four internal operational amplifiers, each amplifiers will have inverting, non inverting and output pins, Power supply pins Vcc and Gnd is common to all internal amplifiers.
Four internal amplifiers in LM3900 works independently with high gain frequency compensation. It requires only one power supply source and also it can operates with split supply. It provide wide band width and large output voltage swing.
This audio mixer circuit requires Regulated DC power supply and audio signals can be directly given as input or can be given after pre-amplification. Provide common ground (Gnd) for all non inverting inputs. Instead of Variable resistors we can use sliding adjustable potentiometer to make the circuit more professional.