FET opamps in the FORMANT

FET opamps in the Formant elektor february 1980 — 2-09 15V Hitopamps In the Kormant At several points in the Formant music synthesiser circuits (described in Elektor, May 1977 .... April 1978), FET source followers are used as high- impedance output buffers. This type of stage is not always the best solution and an alternative is well worth considering: an operational amplifier with an FET input stage. This article will examine the use of these more up- to-date components and will give a description of ways to adapt the VCO"s. voltage, with respect to the input voltage. This must be compensated in one of the following stages. 4. The dynamic range is relatively small. 5. The gate-source bias voltage is tempe- rature-dependent and therefore the output voltage tends to drift. These disadvantages are not so serious — they don"t limit the Formant"s potential as a musical instrument. Nevertheless, it is better to avoid them altogether by replacing the FET source follower circuit (fi...