This circuit for audio signals was found in the March 1990 Radio Electronics magazine. The circuit uses a unusual optocoupler that can be replaced with an equivalent one.
This amplifier was found in a Japanese publication in 1972. Transistors are uncommon today, and...
The current of this source is 200 mA at the most, and the output depends on the zener that may...
Found in Mallory documentation from 1968 this circuit uses an integrated circuit from that time. The...