This interesting circuit for the RDA8851 allows you to obtain two volumes with a simple touch. The circuit is from an Electronics Now from December 1988. Note the amplifier voltages.
This circuit was found in General Electric documentation from 1964. It makes use of a PUT, called the...
This circuit was obtained in a documentation from the 70s. The operational amplifiers used are...
This circuit was found in a documentation for radio amateurs in 1974. It can be used to generate...