low-noise microphone pre-amplifier

P. De Bra low-noise microphone pre-amplifier -amp recording the roar of a lion. No single pre can guarantee a linear amplification of that kind of sound and that of a nightingale at a distance of 100 yards, due to the limits of the input sensitivity. The circuit given here, however, is intended to record the nightingale, but definitely not to record a pop singer who looks as if he is about to swallow his microphone. Any transistor produces noise, but to combat this as effectively as possible, noise-free types from a good manufacturer should be selected. On top of that, the circuit should make optimum use of the transistor noise characteristic. It will be noticed immediately that the circuit described here contains 5 parallel stages. The noise generated by each stage can be added in the manner of a vector power, that is, as the square root of the sum of the squares of each component. As the noise of each stage is slightly out of phase, the resultant figure will be slightly lower th...