This circuit was obtained in an Electronics World of 1968. The operational amplifiers ones are types of the time, no longer used today. The circuit responds from less than 20 Hz.
An interesting option is the one that makes use of the MC3373 integrated circuit and which is...
We found this circuit in a Radio Electronics from February 1970. The frequency of 1,400 kHz in the...
This power step drains just 3.5 mA from the battery and can provide good playback on a 4-ohm...