We found this circuit in a 90s Popular Electronics. The circuit uses a pickup coil that consists of 100 to 200 turns of wire 28 around the cable to be monitored.
This ultra-low noise amplifier and simple power supply was found in Analog Devices documentation from the...
This interesting bandpass filter using an operational amplifier 741 has its cutoff frequency...
Found in a 1968 EEE, this circuit uses transistors from that time. The output is 300 ns....