Found in a 1967 Electronics World, this preamplifier uses an integrated circuit from that time, difficult to obtain today. The maximum frequency is 15 kHz.
This circuit that can only be used with simple resistive and inductive loads (never electronic) was...
This digital instrument input circuit was found in the September 1989 issue of Radio Electronics...
This circuit was found in an 80s documentation. The integrated circuit used is from that time,...