Mic pre amp made by the IC 741 is designed for dynas and works with a voltage source of 12 VDC. If you want to use this pre amp for electret or condenser mic is necessary in adding the 10K resistors on the input line (negative pin C1) which serves to provide a source or bias voltage on the electret microphone. Mic pre amp is fairly simple and easy in assembly because there are no special settings required in the manufacture of a series of mic pre amps with this IC 741.
Microphone pre ampbuilt with IC741 above are set as non-inverting . Gain factor of the microphone pre amp IC 741 is determined by the value of R1 and R2 in which the formula factors microphone pre amp gain is (1 + (R2/R1)). For your consideration, the greater the level of reinforcement of the mic pre amp is the more high-sensitivity or sensitivity of the microphone sound reception, so it is also more vulnerable to noise.