Introduction to Electret Microphone Capsule Wiring
Electret microphone capsules (also called electret mics) are widely used in modern audio devices, such as smart speakers, Bluetooth headsets, and voice-controlled systems. These microphones contain an internal Field Effect Transistor (FET) that requires a DC bias voltage to function properly.
Correct wiring of the electret microphone capsule to your circuit is crucial for stable performance and high-quality audio capture. There are two common wiring methods: source output and drain output. Each has its own advantages and is suitable for different applications.
Source Output Wiring for Electret Microphones
Connection Details: Drain (D) is connected to the positive power supply (VCC). Source (S) is connected to ground through a resistor (Rs) to provide bias voltage. Signal output is taken from the source via a coupling capacitor (C). The shield braid wire is connected to ground for noise reduction.
Advantages: This wiring provides low output impedance (less than 2 kΩ), which ensures circuit stability and a wide dynamic range, making it ideal for high-fidelity audio. It also offers better noise immunity due to stable biasing.
Considerations: The output signal amplitude tends to be lower compared to drain output wiring.
Drain Output Wiring for Electret Microphones
Connection Details: Drain (D) is connected to VCC via a drain resistor (RD). Signal output is taken from the drain through a coupling capacitor (C). Source (S) and the shield braid are connected directly to ground.
Advantages: This method provides voltage gain, resulting in higher microphone sensitivity. It features simpler wiring with only two leads and is common in low-power and compact device designs.
Considerations: The dynamic range is slightly narrower than with source output wiring.
Choosing Resistor Values and Power Supply Voltage
Resistors Rs and RD are usually selected between 2.2 kΩ and 5.1 kΩ depending on the power supply voltage. For example, with a 6V power supply, Rs is often 4.7 kΩ and RD 2.2 kΩ. If the power supply uses a negative ground, swapping the drain and source connections will maintain the output configuration.
Important Notes
Regardless of whether you use source output or drain output wiring, electret microphone capsules require a DC voltage supply to operate because they contain an internal FET.
Choosing the right wiring method and bias components is key to optimizing microphone sensitivity, noise performance, and circuit stability, especially for applications like Bluetooth headsets, voice assistants, noise-canceling microphones, and other audio devices.
