ECM Mic Preamplifier

A microphone amplifier that may be used with either Electret Condenser Microphone (ECM) inserts or dynamic inserts, made with discrete components. Both transistors should be low noise types. In the original circuit, BC650C which is an ultra low noise device was used. These transistors are now hard to find but BC549C or BC109C are a good replacement. The circuit is self biasing and will set its quiescent point at roughly half the supply voltage at the emitter of the last transistor. The electret condenser microphone (ECM) contains a very sensitive microphone element and an internal FET preamp, a power supply in the range 2 to 10 volts DC is therefore necessary. Suitable ECMs may be obtained from Maplin Electronics.

The described circuit is an amplifier specifically designed for microphones, capable of being used with Electret Condenser Microphone (ECM) inserts or dynamic inserts. The construction of this amplifier is based on discrete components, which indicates a design that favors individual parts over integrated circuits, potentially for the sake of easier modification or repair.

The amplifier employs two transistors, both of which should be of low noise types to ensure minimal interference and distortion in the amplified signal. The original design used a BC650C transistor, known for its ultra low noise properties. However, due to their rarity in the present market, the BC549C or BC109C transistors are recommended as suitable replacements. These alternatives also boast low noise characteristics, making them a fitting choice for this application.

Furthermore, the circuit possesses a self-biasing feature, which automatically adjusts its operating point or quiescent point. This point is set at approximately half the supply voltage at the emitter of the last transistor. This self-biasing feature simplifies the design and operation of the circuit, as it negates the need for manual biasing.

The Electret Condenser Microphone (ECM) used in this circuit includes a highly sensitive microphone element and an internal FET preamp. This preamp requires a power supply within the 2 to 10 volts DC range, making it crucial to ensure the power supply falls within this range for proper operation. Maplin Electronics is suggested as a source for suitable ECMs, indicating their availability and compatibility with this design.A microphone amplifier that may be used with either Electret Condenser Microphone (ECM) inserts or dynamic inserts, made with discrete components. Both transistors should be low noise types. In the original circuit, I used BC650C which is an ultra low noise device. These transistors are now hard to find but BC549C or BC109C are a good replacement. The circuit is self biasing and will set its quiescent point at roughly half the supply voltage at the emitter of the last transistor.

The electret condenser microphone (ECM) contains a very sensitive microphone element and an internal FET preamp, a power supply in the range 2 to 10 volts DC is therefore necessary. Suitable ECM`s may be obtained from Maplin Electronics. 🔗 External reference