fm stereo decoder

This part of my site features a stereo decoder circuit suitable for both my pulse counting FM Receivers and other types of FM Tuner, such as the old valve type that incorporates a Foster Seeley or Ratio Detector. This particular stereo decoder IC, MC1310P was popular during the mid 1970s in music centres and for hi fi enthusiasts that wanted to co
fm stereo decoder - schematic

nvert there old mono tuners to stereo. Before this MC1310P IC was around, building a stereo decoder was a difficult task and was actually harder to set up and align then the FM Receiver itself, obvious because you had the 19KHZ and 38KHZ pot core coils to wind which required 1000s of turns of enamelled copper wire in the bargain. You also needed at least 5 valves or 10 transistors to get a decoder that really performed well. Many people have been led to believe that you just hook up the line output from an existing mono FM receiver to the decoder and hope for the best. This is one of the worst pitfalls to get into and I am going to do a brief explanation of how to avoid this. Picture 3 is a typical Foster Seeley FM discriminator found in old transistor portables and valve Hi FI tuners. The output filter capacitor C3 and the R3 are the De-Emphasis components required to receive mono reception. These components vary in value and in this particular discriminator it is set at a time rate of 50 microseconds for UK FM broadcasting. If you simply leave these components in and connect the stereo decoder, you will get very disappointing results because these components will severely distort the 19KHZ pilot tone and stereo signal components leading to poor separation. Picture 4 is the same Foster Seeley discriminator except the De-Emphasis components, R3 and C3 are not included. This later circuit should now be ok for a stereo...

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