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.
The 2009 project is based on the integrated circuit9 LM317T, an adjustable regulator with 3...
This is a traditional 741 configuration with gain close to 100. We found it in the December 1972...
This differentiator for the positive front of the input signal can be elaborated based on any...