stereo dynamic preamplifier

6 stereo dynamic preamplifier A few years have gone by since the first "integrated" stereo dynamic pre- amplifier was published in Elektor. It l was designed around one of the first cL dual low-noise opamps, the 739. Meanwhile, the IC repertoire of oon many manufacturers has grown to such an extent that there is now plenty of choice of opamps suitable C1 for this purpose. This includes ID several with excellent characteristics 1p 6V leaving the seven year old 739 on the shelf. It is therefore high time to discuss a new IC dynamic pre- amplifier. The one selected is the LM 387 from National. It is an easily obtainable, 8 pin device con- taining two very low-noise opamps. The circuit diagram shows how 1000 simple it is to use it to build a high quality dynamic preamplifier. The input impedance has the standard value of 47 k, and is almost exclusively determined by the value of R1. R1 (metal film) may be altered for cartridges requiring a different terminal impedance, to achieve a st...