This circuit is from an American documentation from 1975. The circuit uses components of the time which can be replaced by modern equivalents. The coupler is homemade with a lamp and a photocell.
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...