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.
USB58xx and USB59xx Devices Integrate a 2:1 Multiplexer to Support Reversible Connection of USB...
This circuit, shown in the figure, consists of a variable gain amplifier with differential input...
This configuration can be applied to other transconductance operationals. The circuit has a gain...