This circuit is from an Electronics World of 1968. The transistors are of the time and the power is supplied with a voltage of 40 V. The circuit is high fidelity.
Other CMOS gates can be used in this sensor, which we found in the July 1995 Electronic Now...
This Texas Instruments integrated circuit, available from Mouser Electronics, has a 91 dB common...
This circuit was obtained from an English magazine from 1979, but it can be easily assembled today...