We found this circuit in a 1967 documentation. The integrated circuit and an operational one of the time. Modern equivalents can be tried out. The power supply is symmetrical.
We can implement this filter with more modern equivalent operational amplifiers, since the LM110 is...
This stethoscope or amplifier for hearing aid using a crystal headset and microphone was found in a...
The normal use of a 4520 as a divide-by-16 counter is shown in Figure bellow. In the normal...