This was a National Semiconductor Application Note, now TI. – Low Cost IC Stereo Receiver. The LM3089 FM IF System does all the major functions necessary for FM processing, including a three stage amplifier/limiter and balanced product detector, as well as an audio preamplifier.
FM stereo demodulation is accomplished by the use of the LM1800 phase locked loop, thereby eliminating the need for external coils.
The AM function of the receiver is done completely with the LM3820 AM radio system. While designed for 3 section tuned superheterodyne application.
The LM382 dual preamplifier was selected for its minimum parts count and low noise capability.
Panel meters are employed in the FM system for both signal strength and center tuning, allowing for easy and accurate tuning. A directly driven LED offers immediate indication of FM stereo reception.
A single transistor tone control circuit was designed as the optimum cost/performance trade-off. The transistor is configured in a shunt-shunt feedback design, allowing gain variations between input functions.
The stereo power section, consisting of the LM378 dual audio amplifier, delivers 3W/channel with total harmonic distortion (THD) less than 1% and 4W/channel with THD less than 10%,