Frequency multiplier

Multi Channel Audio Mixer Circuit using LM3900

The technique of integrating numerous audio channels into one or more audio channels is known as audio mixing. Source signals, frequency content, dynamics, loudness, and panoramic position are all adjusted during this process. This Multi Channel audio mixing procedure is utilised in sound recording to create a more appealing output for listeners.

In order to make an album or single, audio mixing is also done in studios. The mixing engineer is usually in charge of the audio mixing process. Audio mixing is currently done on a PC (personal computer) by artists and engineers. This post will show you how to create a multi-channel audio mixer with the help of the LM3900 quad amplifier. There are two MIC inputs and two line inputs on this audio mixing circuit. Add the identical circuit in parallel with the existing circuit if you wish to increase the input channels according to the application. Get a sense of how a simple audio tone control circuit works before learning about this circuit.


  • 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

Circuit Components:

  • 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 is the circuit’s major component. The inverting terminal of the op amp is linked to each input channel of the audio mixer. Each stage’s operational amplifier amplifies each input signal separately. Each op amp’s output is sent to a single output line with a resistance of 470 ohm. The input impedance of this circuit is too high to blend optimal audio input channels. For decoupling purposes, polarised capacitors C1 to C4 are connected to the input channels. Capacitor C5 is the output decoupling capacitor. Each input channel is connected to a variable resistor here. The volume of the associated input channel is adjusted using this variable resistor.

LM3900 Quad Operational Amplifier: 

This IC is made up of four Norton amplifiers with high gain and frequency compensation. These operational amplifiers are intended to function over a wide voltage range. Almost all signal frequencies are well-received by these amplifiers. This IC has a significant output voltage swing and a wide band width. Short-circuit safety is included into this IC.

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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