Designing a simple audio mixer circuit for multiple input sources can be done using basic electronic components. Here's a step-by-step guide on how to create a basic 2-channel audio mixer using analog circuitry:
Components needed:
Two or more audio input sources (e.g., smartphones, computers, microphones, etc.).
Audio potentiometers (potentiometers with logarithmic taper) for volume control of each input.
Resistors and capacitors (values will depend on the specific requirements).
An operational amplifier (op-amp) - commonly used op-amps like LM741 or LM358 will work for simple applications.
A power supply (e.g., a dual power supply or a single supply with virtual ground) to power the op-amp.
Step-by-step guide:
Signal Conditioning:
Start by connecting each audio input source to its respective volume control potentiometer. This will allow you to adjust the volume of each input independently.
To connect an input source, wire one terminal of the potentiometer to the audio input signal, and the other terminal to ground (GND).
The middle terminal (wiper) of the potentiometer will be connected to the next stage of the mixer circuit.
Summing Amplifier:
After the potentiometers, connect each wiper to a summing amplifier circuit. This circuit will sum the individual input signals together.
Use an op-amp in an inverting configuration as the summing amplifier. Connect the wiper of each potentiometer to the inverting input (-) of the op-amp.
Connect a feedback resistor (Rf) from the output of the op-amp back to the inverting input (-). The value of Rf can be chosen based on the desired gain (typically set to 1).
Use a resistor (R1) from the inverting input (-) to ground (GND) to provide a reference for the input signals.
Connect a capacitor (C1) between the inverting input (-) and ground (GND) to block any DC offset.
Non-Inverting Amplifier (optional):
If you need to boost the overall output level of the mixer, you can add a non-inverting amplifier at the output of the summing amplifier.
Use another op-amp in a non-inverting configuration for this stage.
Connect a feedback resistor (Rf) from the output of the op-amp to the inverting input (-).
Connect a resistor (R2) from the non-inverting input (+) to ground (GND).
Connect a capacitor (C2) between the non-inverting input (+) and ground (GND) to block any DC offset.
Output Stage:
Connect the output of the non-inverting amplifier (if used) or the output of the summing amplifier (if not using the non-inverting amplifier) to the audio output, which can be a speaker or a line-level output to be connected to external equipment.
Power Supply:
Ensure that the op-amp is powered with a suitable power supply. You can use a dual power supply or a single supply with a virtual ground (created using voltage divider circuit) depending on the op-amp you are using.
Remember to double-check all connections, component values, and the pinout of the op-amp you're using before powering on the circuit. Also, consider adding bypass capacitors across the power supply pins of the op-amp to reduce noise and improve stability.
Keep in mind that this is a basic audio mixer circuit design. Depending on your specific requirements, you might need to incorporate more sophisticated features, such as tone controls, pan controls, or mute switches. Additionally, for higher-quality audio applications, you may want to use higher-grade op-amps and incorporate measures to reduce noise and interference.