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.
The CUT frequency for this filter is determined by the capacitors. The µA4138 is a quad version of...
We found this circuit from a commercial megaphone in a Japanese publication in 1967. The circuit is...
Using in operational amplifier is possible to increase the dissipation power of a zener. This...