This low power bass booster is from the 1977 National Semiconductor Audio Handbook. The circuit is powered by 6 to 9 V voltages and the feedback determines the enhanced bass range.
We found this receiver circuit for modulated light in a 90s Popular Electronics. Equivalent audio...
This field strength meter circuit was found in the March 1968 Radio Electronics magazine. The...
I found this circuit in a 1998 publication, but as all components are common, it can be easily...