dynamic pre-amplifier - for magnetic pick-ups

dynamic pre-amplifier elektor october 1984 The design incorporates a few special characteristics that make it a little more than just another pre-amplifier. It is in- tended primarily for fitting in the record player. Such an arrangement precludes the use of a long feeder cable between the pick-up and the main amplifier. A lengthy feeder cable is a source of hum and adds a considerable capacitive load across the pick-up. Because the length of the cable would vary from installation to installation, it would be impossible to put a value to the capacitance. Yet, to achieve a straight frequency characteristic, it is imperative that the pick-up is terminated into the correct impedance. The induct- ance of the pick-up coil and the input capacitance of the pre-amplifier form a resonant circuit, the frequency of which is used by the manufacturers to get the high- frequency end of the characteristic right. A capacitive mismatch therefore causes either a premature fall-off in high fre- quen...