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, in addition to transforming a sinusoidal signal into a square, shifts its phase. The...
The transistors on this circuit can be the BC548. The circuit is from English documentation from...
In the figure we have three voltage doubler configurations that can be used in high and low...