This circuit is from LinearTechnology Applications of 1997. The circuit uses components of the time used to raise the voltage of a battery from 3 to 6 V.
We found this circuit in a 1998 documentation. The circuit can also be used as a minutery...
The TAA131 used in this circuit is not very easy to find today, but an equivalent low power audio...
These three circuits have different treble responses. We found them in the February 1970 issue of...