I found this circuit in an old document from 1981. The circuit can be implemented today with the BC549 transistor. Power can be supplied with a 9 V battery, as consumption is very low. The signal input and output cables must be shielded.

I found this circuit in an old document from 1981. The circuit can be implemented today with the BC549 transistor. Power can be supplied with a 9 V battery, as consumption is very low. The signal input and output cables must be shielded.