AmplifierCircuits

The preamplifier amplifies the output signal of a microphone, so that it can be. The further amplified by a power amplifier The circuit provides an output signal line. With two transistors, it is not difficult to build such a circuit. The amplifier produces little noise. In the shown embodiment, the circuit is suitable for microphones 500 and 600 Ω. 200 Ω R1 microphones should be reduces to 220 Ω and C1 should be increased to 4.7 uF. The gain is set by R2. If the average declared value of 22 K? Can be used. The maximum gain is about 200times. R1 = 470 Ω R 2 = 22 K? R3 = 12 K? R4 = 47 k R5 = 820 Ω R6 = 100 Ω R7 = 1 k R8 = 100 k C1, C4 = 2.2 V μF/16 C2 = 47 V μF/16 C3 = 470 nF T1 = BC 549C T2 = BC 547B

This is a good pre-amplifier for microphones that can be. Used in, for example, mixing consoles The circuit operates with a dual op-amp type NE 5532. The amplifier must be adjusted. Simply plug the power and control over P1 such that half the supply voltage (6 V) on pin 3 of IC1 state. P2 is then adjusted to the desired volume. R1 = 8,2 kW R2, R4, R5, R6 = 10 kW R3 = 1 k P1 = 4.7 K? P2 = 100 k C1, C2, C4, C6 = 10 uF C3 = 470 nF C5 = 100 nF IC1 NE = 5532

This circuits allows you to use a cheap loudspeaker as a microphone. Sound waves reaching the speaker cone cause fluctuations in the voice coil. The voice coil moving in the speakers magnetic field will produce a small electrical signal. The circuit is designed to be used with an operating voltage between 6 and 12 volts dc. The first transistor operates in common base mode. This has the advantage of matching the low input impedance of the speaker to the common base stage, and secondly has a high voltage gain. The second stage is direct coupled and operates in emitter follower. Voltage gain is slightly less than unity, but output impedance is low, and will drive long cables. Speech quality is not as good compared to an ordinary or ECM microphone, but quite acceptable results can be obtained. Speaker cones with diameters of 1 inch to 3 inches may be used. Speaker impedance may be 4 ohm to 64 ohm. The 8.2 ohm resistor value may be changed to match the actual speakers own impedance. ...

I decided to make this circuit so that I could listen to faint noises. It is a simple two-stage transistor amplifier design. The circuit was designed to use the input from a dynamic microphone but I am sure that with some modifications it would be possible to use an electret microphone. The 2N3053 transistors used in the design don’t have a particularly high gain so other types could probably be used as long as they are NPN. source: eleccircuit.com

      This circuit was submitted by Lazar Pancic from Yugoslavia. The sound card for a PC generally has a microphone input, speaker output and sometimes line inputs and outputs. The mic input is designed for dynamic microphones only in impedance range of 200 to 600 ohms. Lazar has adapted the sound card to use a common electret microphone using this circuit. He has made a composite amplifier using two transistors. The BC413B operates in common emitter to give a slight boost to the mic signal. This is followed by an emitter follower stage using the BC547C. This is necessary as the mic and circuit and battery will be some distance from the sound card, the low output impedance of the circuit and screened cable ensuring a clean signal with minimum noise pickup. original article soruse: eleccircuit.com

BC549C and BC547B m icrophone  general description: The preamplifier amplifies the output signal of a microphone, so that it can be. The further amplified by a power amplifier The circuit supplies the output to a signal line.  With two transistors, it is not difficult to build such a circuit. The amplifier produces little noise. In the shown embodiment, the circuit is suitable for microphones 500 and 600 Ω. 200 Ω R1 microphones should be reduces to 220 Ω and C1 should be increased to 4.7 uF.  The gain is set by R2. If the average declared value of 22 K? Can be used. The maximum gain is about 200 times. BC549C and BC547B m icrophone  circuit: BC549C and BC547B m icrophone  part list: R1 = 470 Ω R 2 = 22 K? R3 = 12 K? R4 = 47 k R5 = 820 Ω R6 = 100 Ω R7 = 1 k R8 = 100 k C1, C4 = 2.2 V μF/16 C2 = 47 V μF/16 C3 = 470 nF T1 = BC 549C T2 = BC 547B