Frequency multiplier

Multi Channel Audio Mixer Circuit using LM3900

The process of blending multiple audio channels into one or more audio streams is referred to as audio mixing. It involves adjusting source signals, frequency content, dynamics, loudness, and spatial positioning. This multi-channel audio mixing technique is commonly used in sound recording to produce a more appealing output for listeners.

Audio mixing is also performed in studios to create albums or singles. Typically, the audio mixing process is overseen by a mixing engineer. Nowadays, artists and engineers are able to perform audio mixing on personal computers (PCs).

In this article, we’ll demonstrate how to construct a multi-channel audio mixer using the LM3900 quad amplifier. The circuit features two MIC inputs and two line inputs for audio input. If you need more input channels for your specific application, you can replicate the same circuit in parallel. To better understand this circuit, it’s helpful to have a grasp of how a basic audio tone control circuit functions.


  • Circuit Diagram of Multi Channel Audio Mixer using LM3900:
    • Multi Channel Audio Mixer using LM3900 Circuit Design:
      • LM3900 Quad Operational Amplifier:  
    • Multi Channel Audio Mixer Circuit Features:
    • How to Operate Multi Channel Audio Mixer Circuit using LM3900?
    • Multi Channel Audio Mixer Circuit Applications:

Circuit Diagram of Multi Channel Audio Mixer using LM3900:

Multi Channel Audio Mixer

Circuit Diagram of Multi Channel Audio Mixer using LM3900


  • LM3900 Quad operational amplifier
  • 1k PRESET – 4
  • MICs – 2
  • 0.47uF Electrolytic capacitor – 2
  • 0.1uF Electrolytic capacitor – 2
  • 0.1uF capacitor – 1
  • 1Ω Resistor (1/4 watt) – 2
  • 1M ohm resistor (1/4 watt) – 4
  • 470 ohm resistors (1/4 watt) – 6
  • 330 ohm resistors (1/4 watt) – 2
  • Connecting wires.
  • Power supply circuit

Multi Channel Audio Mixer using LM3900 Circuit Design:

The LM3900 quad operational amplifier plays a central role in this circuit. The inverting terminal of the operational amplifier is connected to each audio mixer input channel. Each operational amplifier stage individually amplifies the input signal from each channel. The output from each op amp is combined into a single output line through a 470-ohm resistor. The input impedance of this circuit is set quite high to effectively blend various audio input channels. For decoupling purposes, polarized capacitors C1 to C4 are linked to the input channels, while capacitor C5 serves as the output decoupling capacitor. Each input channel is associated with a variable resistor, which is employed to adjust the volume of the respective input channel.

LM3900 Quad Operational Amplifier: 

This IC comprises four Norton amplifiers designed with high gain and frequency compensation. These operational amplifiers are engineered to operate effectively across a broad voltage range and can accommodate nearly all signal frequencies. The IC offers a substantial output voltage range and boasts a wide bandwidth. Additionally, it incorporates short-circuit protection features for added safety.

LM3900 IC

Pin Description:

  • 1IN+: The first operational amplifier’s non-inverting terminal.
  • 2IN+: The second operational amplifier’s non-inverting terminal.
  • 2IN-: The second operational amplifier’s inverting terminal.
  • 2OUT: The second op amp’s output terminal.
  • 1OUT: The first op amp’s output terminal.
  • 1IN-: The first operational amplifier’s inverting terminal.
  • GND is the pin that connects to the ground.
  • 3IN-: The third op amp’s inverting terminal.
  • 3OUT: The third op amp’s output terminal.
  • 4OUT: The fourth op amp’s output terminal.
  • 4IN-: The fourth operational amplifier’s inverting terminal.
  • 4IN+: The fourth operational amplifier’s non-inverting terminal.
  • 3IN+: The third operational amplifier’s non-inverting terminal.
  • VCC: We can use this to apply voltages ranging from 4.5 to 32 volts.

Refer to the LM3900 Datasheet for more information on the IC.

Between 5 and 30 volts can be used to power this audio mixer circuit. Connect a 100uF/60V capacitor between the supply and ground pins if the supply circuit is remote from the audio mixing circuit.

Multi Channel Audio Mixer Circuit Features:

  1. Wide range of source voltages
  2. Input current is low (30nA)
  3. The open loop gain is really strong, and the design is simple. The frequency response is excellent.
  4. Low decibels
  5. Protection against short circuits at the output

How to Operate Multi Channel Audio Mixer Circuit using LM3900?

  1. To begin, connect the components as shown in the circuit diagram.
  2. Ensure that the output is well regulated when providing the power supply.
  3. Give the audio inputs now.
  4. You’ll obtain a mixed audio stream at the output of the audio mixer.

Multi Channel Audio Mixer Circuit Applications:

  • This audio mixer is used in sound recording to provide more appealing sounds for listeners.
  • Used in recording studios to create albums.

Limitations of the Circuit:

This circuit is being researched conceptually, but it may need to be tweaked before it can be used in practise.


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