We found this circuit in a 1977 documentation. The National Semiconductor's LM380 is no longer easily found, but if used on this amplifier it provides excellent reproduction quality.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...