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.
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
The presented circuit uses an operational one of the time. The circuit is from an 80's manual and...
The operation of this circuit is old, but the configuration can be elaborated based on modern...