We found this preamplifier with 70 dB gain for microphones in American documentation from the 90's. Consumption is low and equivalent transistors can be used.
This circuit was obtained from an English publication from the 70's. The circuit is still current for...
This circuit was found in a 1979 magazine. We can use any JFET like MPF102 or BF245. The relay is 12 V...
Found in Motorola documentation from the 90s, this circuit can be implemented with current...