The operational amplifier used is not common today, but the circuit can be implemented with modern operational ones. The gain is 1000 and the source must be symmetrical.
We found this simple circuit with headphones listening in Radio Electronics magazine from March...
This circuit was obtained from Maxim documentation. The circuit has 4.5 and 5.5V thresholds for...
This complementary-output amplifier can be used to source a good qualuty signal to high impedance...