This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even adapted to act as a shield. The circuit has the frequency given by C1 and adjusted in R1.
We found this 4-channel mixer in the August 1999 issue of Electronics Now magazine. The circuit can...
The configuration shown makes use of a simple source and the gain is given by the relationship between R3...
This circuit was found in a 1995 documentation and is very simple to assemble, as the components are...