This harmonic oscillator controlled by crystal was found in an American documentation of the 90's. The circuit uses transistors of the time. Current equivalents can be used.
Pressing and releasing S1 remains one of the neon lamps. Which one will be, it is not possible to...
This circuit, which appears on our website in different versions, uses an integrated VU which is...
This VCA was found in the July 1988 issue of Radio Electronics magazine. It uses an OTA op amp and...