Audio Preamplifier (Two Transistors)
This circuit can be use for mic or any input for increasing audio of weak signals. The preamplifier discussed previously was using one transistor for amplifying mic signals but this circuit is using two transistors to further increasing the gain. The transistor shown in this circuit are making stabilized amplifier and providing high gain at medium impedance, they provide a gain of 12 on high input impedance.
In this circuit transistor 1 (BC 183) and transistor 2 (BC 478) provides a direct coupled amp. Resistor 1 and resistor 2 are forming operating bias and resistor 4 is providing temperature stabilization. This preamplifier circuit generates a gain of more than 90 times with 20 KHz frequency response. The Capacitor 4 and resistor 5 are providing supply line filtration. If you want to design the circuit for negative supply then reverse the polarity of capacitors and interchange transistor 1 and transistor 2.
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