This circuit from an old Motorola manual uses an integrated circuit that is no longer easily found. The circuit can be designed with more modern operating systems and the supply voltage can be changed to the range of 9 to 12 V, with a symmetrical source. The circuit has a gain of 40 dB and a passing range of 20 Hz to 20 kHz. Signal cables must be shielded, and the source must have excellent filtering. Component values can be approximated to current standards.
