Super low noise pre-amplifier - for magnetic cartridges

7-72 - elektor july/august 1982 Preamplifiers for magnetic cartridges suffer from one major problem: Their own noise. This additional noise is produced mainly by the irregular current flow in the PN junction of the input transistor. The cause of this "irregularity" is due to manufacturing tolerances. Some manufacturers, especially Japanese have designed extremely low noise transistors, but unfortunately these components are very hard to find and rather expensive. For these reasons this circuit uses the physical law that voltages of non- correlating noise sources that are con- nected in parallel add geometrically, thus reducing the over-all noise of the parallel circuit. This magnetic preamp contains 8 transistors that are con- nected in parallel thus lowering the noise by factor V8-, which is 2.82 or 9 dB. The completely symmetrical circuit and the class A mode output transistor stage, formed by T17 and T18, allows low distortion factors that cannot be reached by any integrated ...