multi channel audio mixer using lm3900

Description: The circuit includes a quad channel amplifier (LM3900) with microphone audio inputs and direct line inputs. By adding circuits in parallel, the number of inputs can be increased for various applications. The input is connected to the inverting terminal of the LM3900. Each section of the amplifier amplifies the audio input separately, which is then fed to the output terminals. The output terminal from each channel is connected to the output line through a resistor of no more than 680K, producing a mixed audio output with low noise. This audio mixer circuit does not utilize ideal impedance input sources. Capacitors C1 to C4 serve as decoupling capacitors for their respective channels, while C5 is the output decoupling capacitor. The LM3900 series consists of four internally compensated amplifiers designed for single and wide power voltage applications. These voltage input amplifiers exhibit a good response across all audio frequencies and provide a suitable output swing.

The circuit utilizes the LM3900 quad operational amplifier, which is known for its versatility in audio applications. Each of the four amplifiers within the LM3900 is configured to handle individual audio inputs, allowing for simultaneous processing of multiple signals. The inverting configuration ensures that the audio signals are amplified while maintaining phase integrity, which is crucial for audio mixing.

The choice of a resistor value not exceeding 680K at the output terminal is significant for maintaining signal integrity and minimizing noise levels. This resistor acts as a load for the amplifier, ensuring that the output signal remains within acceptable limits while preventing distortion. The mixed output, characterized by low noise, is essential for high-fidelity audio applications.

Decoupling capacitors (C1 to C4) are strategically placed to filter out high-frequency noise and stabilize the power supply for each channel. This is particularly important in audio applications where clarity and fidelity are paramount. The output decoupling capacitor (C5) further enhances the quality of the mixed audio signal by blocking any DC offset that may be present, ensuring that only the desired AC audio signal is passed to subsequent stages.

The LM3900's design allows it to operate effectively across a wide range of power supply voltages, making it suitable for various applications in audio engineering. Its ability to respond well to all audio frequencies ensures that the circuit can handle a diverse array of audio signals without significant degradation in sound quality. The output swing capability of the LM3900 enhances its usability in different audio environments, making it a reliable choice for audio mixing and amplification tasks.The circuit consists of channel quad amplifier (LM3900). mic audio inputs and direct line inputs are circuit. By adding circuit parallel with this, increase of inputs the applications. input is connected to the inverting terminal of LM3900. The amplifier of each section amplifies every audio input separately and is fed to the output terminals. The output terminal from channel is connected to output line with a resistance not than 680K and produces a mixed audio at the output with low noise. This audio mixer circuit doesn`t use impedance input ideal sources. Capacitors C1 to C4 are the decoupling capacitors for the corresponding channels. C5 is that the output decoupling capacitor. LM3900 series amplifiers four and internally compensated amplifiers that are designed for single and wide power voltage.

These amplifiers of voltage inputs good response for all audio frequencies. They output swing.