This circuit for frequencies of 20 to 2 kHz was obtained in English documentation from 1966. The transistor can be any general purpose and powered by batteries.
This amplifier uses a 1975 integrated circuit, which is uncommon today. The circuit has a gain of 30...
Using junction FETs, a configurable configuration is achieved for very low frequencies. FETs can...
This 2-terminal regulator was obtained from a 1990s National Semiconductor manual. The components admit...