This circuit is a low-noise, high-quality electret condenser microphone preamplifier that can be used with all microphone types. The supply voltage required for the internal amplifiers inside the electret microphone to operate is also provided separately by the circuit.
Electret Microphone Preamp General Information
Contents
Low-noise microphone preamplifier circuit; is designed to be compatible with different microphone types, including condenser microphones, dynamic microphones, and electret microphone capsules.
Thanks to its compact structure with small dimensions, it can be easily integrated into handmade microphones or audio applications with limited space.
True condenser microphones used in professional and studio environments are generally expensive.
For this reason, electret microphones are widely preferred as a more economical alternative.
Electret capsules absolutely require a supply voltage due to the impedance converter found in their internal structure.
With the TL072 Opamp input arrangement, this circuit also provides the required supply voltage, allowing both 2-pin and 3-pin electret microphone capsules to be used.
Electret Microphone Amplifier Circuit Structure and Operating Principle
The circuit schematic of the microphone preamplifier is shown above. The circuit is powered through the ST1 (+) and ST2 (–) terminals and can operate with voltages between 5 V and 15 V.
The audio (NF) signal from the microphone is applied to terminals ST4 and ST5; here ST5 is the ground (GND) connection. The input impedance is determined by the R3 and R4 resistors and should be selected according to the output impedance of the microphone.
The input impedance can be adjusted by means of the BR2 jumper:
- BR2 closed: low impedance (~600 Ω)
- BR2 open: high impedance (~47 kΩ)
The supply voltage required for an electret microphone with an internal amplifier can be taken from the ST3 terminal.
In 2-pin electret capsules, since the audio signal and supply are transmitted over the same line, the BR1 jumper is closed and the microphone supply voltage (UMic) is applied directly to the ST4 input. At this point, R1, R2, and C1 are used to suppress noise on the supply line.
Pinout and connection information for a 2-pin electret microphone with an integrated FET amplifier
Pinout and connection information for a 3-pin electret microphone with an integrated FET amplifier
Microphone Amplifier Stages
The audio signal coming through ST4 is transmitted to the non-inverting input (Pin 3) of the first TL072 operational amplifier stage (IC1A) through the 220nf C3 coupling capacitor.
This stage provides approximately 20.8 dB (11 times) gain. The gain value depends on the R6 / R5 resistor ratio. The 10uf C2 capacitor provides DC isolation through the 1k R5.
The output of the first stage is applied through the 1k R10 resistor to the inverting input (Pin 6) of the second amplifier stage, TL072 IC1B.
This stage amplifies the signal by approximately another 20 dB (10 times). The gain is determined by the R10 and R11 resistors.
As a result of these two stages, the total gain reaches approximately 40.8 dB. The amplified audio signal is transferred to the output terminal ST6 through the C8 coupling capacitor.
The operating reference point of both operational amplifiers is set to half of the supply voltage (UB / 2). This reference is obtained with the voltage divider formed by the R7 and R8 resistors.
Electret Microphone Connection Options
2-pin electret microphone capsule:
Microphone terminals ST4 (In) and ST5 (GND)
BR1 closed
R3 not installed
3-pin electret microphone capsule:
Terminals respectively ST3, ST4, and ST5 (GND)
BR1 open
R3 not installed
Condenser or dynamic microphone (600 Ω or 47 kΩ):
Signal terminal ST4, shield ST5
BR1 open
BR2 is adjusted according to the microphone impedance
After all connections are made and the supply voltage is applied, the circuit becomes ready to operate.
Note: The Electret Microphone preamp PCB layout was copied with Sprint Layout 6, checked, but not tested. Source .lay6, Gerber, and PDF files are available.
source: de.elv.com/p/smd-mikrofonvorverstaerker-P202458/
