[Photo] ECM microphone preamplifier

Both transistors are 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 BC109C are a good replacement. The circuit is very device tolerant 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. The 1k resistor limits the current to the mic. The output impedance is very low and well suited to driving cables over distances up to 50 meters. Screened cable therefore is not necessary.

The world premiere of the technical zone! ROHM has developed the power supply IC "BD372xx series" for high-quality audio. A practical guide for the purchase of home wireless routers. Understanding the circuit diagram and working principle of the audio. Talking about the "frequency response curve" in the audio. Deep dismantling report of the M0pro speaker: both internal and external

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The positive active material is mainly made of nickel, and the negative active material is mainly an alkaline battery made of cadmium.The nickel-cadmium battery used in AGV car has large internal resistance and can be used for large current discharge.Compared with other kinds of batteries, nickel-cadmium batteries can withstand overcharge or overcharge, and the operation is simple and convenient.The discharge voltage is somewhat different according to the discharge current. In general, the discharge termination voltage of about 1.2v nickel-cadmium battery is 1.0v /CELL, and the actual operating temperature ranges from -20 degrees to 60 degrees. In this range, the discharge can be repeated for more than 500 times.

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