This elaborate mixer is from an Electronics Today International from the 80s. Operational amplifiers are common and resistors with no value determine the gain of the amplification steps.
This filter rejects signals below 300 Hz and signals above 3000 Hz, being used in...
The circuit shown is from the National Semiconductor's Linear Applications Handbook, 1994. The...
We found this capacitive relay circuit in a 1967 Japanese documentation. The circuit is sensitive, and...